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LM2734Z

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LM2734Z/-Q1 Thin SOT 1-A Load Step-Down DC-DC Regulator

1 Features 3 Description

The LM2734Z regulator is a monolithic, high-

1• Qualified for Automotive Applications frequency, PWM step-down DC–DC converter

• AEC-Q100 Qualified With the Following Results: assembled in a thick 6-pin SOT and a WSON non-

– Device Temperature Grade 1: –40°C to 125°C pullback package. The device provides all the active

Ambient Operating Temperature Range functions to provide local DC–DC conversion with fast

transient response and accurate regulation in the

– Device HBM ESD Classification Level 2 smallest possible PCB area.

– Device CDM ESD Classification Level C6 With a minimum of external components and online

• 6-pin SOT Package, or 6-Pin WSON Package design support through WEBENCH™, the LM2734Z

• 3.0-V to 20-V Input Voltage Range is easy to use. The ability to drive 1-A loads with an

• 0.8-V to 18-V Output Voltage Range internal 300-mΩNMOS switch using state-of-the-art

0.5-µm BiCMOS technology results in the best power

• 1-A Output Current density available. The world class control circuitry

• 3-MHz Switching Frequency allows for ON-times as low as 13 ns, thus supporting

• 300-mΩNMOS Switch exceptionally high-frequency conversion over the

entire 3-V to 20-V input operating range down to the

• 30-nA Shutdown Current minimum output voltage of 0.8 V. Switching frequency

• 0.8-V, 2% Internal Voltage Reference is internally set to 3 MHz, allowing the use of

• Internal Soft-Start extremely small surface mount inductors and chip

• Current-Mode, PWM Operation capacitors. Even though the operating frequency is

very high, efficiencies up to 85% are easy to achieve.

• Thermal Shutdown External shutdown is included, featuring an ultra-low

standby current of 30 nA. The LM2734Z uses current-

2 Applications mode control and internal compensation to provide

• DSL Modems high-performance regulation over a wide range of

operating conditions. Additional features include

• Local Point of Load Regulation internal soft-start circuitry to reduce inrush current,

• Battery-Powered Devices pulse-by-pulse current limit, thermal shutdown, and

• USB-Powered Devices output overvoltage protection.

• Automotive Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

WSON (6) 3.00 mm × 3.00 mm

LM2734Z SOT (6) 1.60 mm × 2.90 mm

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

Typical Application Circuit Efficiency vs Load Current

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

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Table of Contents

7.4 Device Functional Modes........................................ 11

1 Features.................................................................. 18 Application and Implementation ........................ 12

2 Applications ........................................................... 18.1 Application Information............................................ 12

3 Description............................................................. 18.2 Typical Applications ................................................ 12

4 Revision History..................................................... 29 Power Supply Recommendations...................... 26

5 Pin Configuration and Functions......................... 310 Layout................................................................... 26

6 Specifications......................................................... 410.1 Layout Guidelines ................................................. 26

6.1 Absolute Maximum Ratings ...................................... 410.2 Layout Examples................................................... 27

6.2 ESD Ratings.............................................................. 411 Device and Documentation Support................. 28

6.3 Recommended Operating Conditions....................... 411.1 Device Support...................................................... 28

6.4 Thermal Information.................................................. 511.2 Documentation Support ........................................ 28

6.5 Electrical Characteristics........................................... 511.3 Community Resources.......................................... 28

6.6 Typical Characteristics.............................................. 611.4 Trademarks........................................................... 28

7 Detailed Description.............................................. 711.5 Electrostatic Discharge Caution............................ 28

7.1 Overview................................................................... 711.6 Glossary................................................................ 28

7.2 Functional Block Diagram......................................... 712 Mechanical, Packaging, and Orderable

7.3 Feature Description................................................... 7Information ........................................................... 28

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision E (April 2013) to Revision F Page

• Added ESD Ratings table, Feature Description section, Device Functional Modes section, Application and

Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation

Support section, and Mechanical, Packaging, and Orderable Information section................................................................ 1

• Removed soldering information ............................................................................................................................................. 4

Changes from Revision D (April 2013) to Revision E Page

• Changed layout of National Data Sheet to TI format ........................................................................................................... 25

Product Folder Links: LM2734Z LM2734Z-Q1

BOOST

GND

VIN

DAP

BOOST

GND

FB EN

VIN

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5 Pin Configuration and Functions

DDC Package

6-Pin SOT

Top View

NGG Package

6-Pin WSON

Top View

Pin Functions

PIN TYPE(1) DESCRIPTION

NAME SOT WSON

Boost voltage that drives the internal NMOS control switch. A bootstrap

BOOST 1 3 I capacitor is connected between the BOOST and SW pins.

DAP — — P The die attach pad is internally connected to GND.

Enable control input. Logic high enables operation. Do not allow this pin to float

EN 4 6 I or be greater than VIN + 0.3 V.

FB 3 1 I Feedback pin. Connect FB to the external resistor divider to set output voltage.

Signal and Power ground pin. Place the bottom resistor of the feedback network

GND 2 2 P as close as possible to this pin for accurate regulation.

SW 6 4 O Output switch. Connects to the inductor, catch diode, and bootstrap capacitor.

VIN 5 5 P Input supply voltage. Connect a bypass capacitor to this pin.

(1) I –Input, O – Output, P – Power

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6 Specifications

6.1 Absolute Maximum Ratings

See (1)(2)

MIN MAX UNIT

VIN Input voltage –0.5 24 V

SW voltage –0.5 24 V

Boost voltage –0.5 30 V

Boost to SW voltage –0.5 6 V

FB voltage –0.5 3 V

EN voltage –0.5 VIN + 0.3 V

TJJunction temperature 150 °C

Tstg Storage temperature –65 150 °C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended

Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and

specifications.

6.2 ESD Ratings VALUE UNIT

Human-body model (HBM), per AEC Q100-002(1)(2) ±2000

Electrostatic

V(ESD) V

discharge Charged-device model (CDM), per AEC Q100-002 ±1000

(1) AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.

(2) Human-body model, 1.5 kΩin series with 100 pF.

6.3 Recommended Operating Conditions MIN MAX UNIT

VIN Input voltage 3 20 V

SW voltage –0.5 20 V

Boost voltage –0.5 25 V

Boost to SW voltage 1.6 5.5 V

TJJunction temperature –40 125 °C

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6.4 Thermal Information LM2734Z

THERMAL METRIC(1) DDC (SOT) NGG (WSON) UNIT

6 PINS 6 PINS

RθJA Junction-to-ambient thermal resistance(2) 180.3 56.2 °C/W

RθJC(top) Junction-to-case (top) thermal resistance 51.6 52.6 °C/W

RθJB Junction-to-board thermal resistance 27.7 30.7 °C/W

ψJT Junction-to-top characterization parameter 1.2 0.9 °C/W

ψJB Junction-to-board characterization parameter 27.3 30.8 °C/W

RθJC(bot) Junction-to-case (bottom) thermal resistance — 10.7 °C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application

report (SPRA953).

(2) Thermal shutdown occurs if the junction temperature exceeds 165°C. The maximum power dissipation is a function of TJ(MAX), RθJA and

TA. The maximum allowable power dissipation at any ambient temperature is PD= (TJ(MAX) – TA)/RθJA . All numbers apply for packages

soldered directly onto a 3-in × 3-in printed-circuit-board with 2-oz. copper on 4 layers in still air. For a 2-layer board using 1-oz. copper in

still air, RθJA = 204°C/W.

6.5 Electrical Characteristics

All typical specifications are for TJ= 25°C, and all maximum and minimum limits apply over the full operating temperature

range (TJ= –40°C to 125°C). VIN = 5 V, VBOOST – VSW = 5 V (unless otherwise noted). Data sheet minimum and maximum

specification limits are specified by design, test, or statistical analysis.

PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT

VFB Feedback voltage 0.784 0.8 0.816 V

ΔVFB/ΔVIN Feedback voltage line regulation VIN = 3 V to 20 V 0.01 % / V

IFB Feedback input bias current Sink and source 10 250 nA

Undervoltage lockout VIN Rising 2.74 2.90

UVLO Undervoltage lockout VIN Falling 2 2.3 V

UVLO hysteresis 0.30 0.44 0.62

FSW Switching frequency 2.2 3.0 3.6 MHz

DMAX Maximum duty cycle 78% 85%

DMIN Minimum duty Cycle 8%

VBOOST - VSW = 3 V 300 600 mΩ

(SOT Package)

RDS(ON) Switch ON resistance VBOOST - VSW = 3 V 340 650 mΩ

(WSON Package)

ICL Switch current limit VBOOST - VSW = 3 V 1.2 1.7 2.5 A

Quiescent current Switching 1.5 2.5 mA

IQQuiescent current (shutdown) VEN = 0 V 30 nA

IBOOST Boost pin current (Switching) 4.25 6 mA

Shutdown threshold voltage VEN Falling 0.4

VEN_TH V

Enable threshold voltage VEN Rising 1.8

IEN Enable pin current Sink/source 10 nA

ISW Switch leakage 40 nA

(1) Specified to Texas Instruments' Average Outgoing Quality Level (AOQL).

(2) Typicals represent the most likely parametric norm.

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6.6 Typical Characteristics

at VIN = 5 V, VBOOST - VSW = 5 V, L1 = 2.2 µH and TA= 25°C (unless otherwise noted)

VOUT = 5 V VOUT = 3.3 V

Figure 1. Efficiency vs Load Current Figure 2. Efficiency vs Load Current

VOUT = 1.5 V

Figure 3. Efficiency vs Load Current Figure 4. Oscillator Frequency vs Temperature

VOUT = 1.5 V IOUT = 500 mA VOUT = 3.3 V IOUT = 500 mA

Figure 5. Line Regulation Figure 6. Line Regulation

Product Folder Links: LM2734Z LM2734Z-Q1

BOOST

Output

Control

Logic

Current

Limit

Thermal

Shutdown

Under

Voltage

Lockout

Corrective Ramp

Reset

Pulse

PWM

Comparator

Current-Sense Amplifier RSENSE

Internal

Regulator

and

Enable

Circuit

Oscillator

Driver 0.3:

Switch

Internal

Compensation

GND

Error Amplifier -

+VREF

0.8V

COUT

OFF

VBOOST

VSW

CBOOST

VOUT

CIN

VIN

ISENSE

-0.88V

OVP

Comparator

Error

Signal

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LM2734Z-Q1

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7 Detailed Description

7.1 Overview

The LM2734Z is a constant frequency buck regulator that can deliver load current of 1 A. Device is optimized for

high-efficiency operation and includes a number of features that make it suitable for demanding applications.

High switching frequency allows for use of small external components enabling small solution size and saving

board space.

Device is designed to operate from wide input voltage range up to 20 V, making it ideal for wide range of

applications (such as automotive, industrial, communications, and so forth). LM2734Z can be controlled through

shutdown pin, consuming only 30 nA in standby mode, making it very appealing for applications that demand

very low standby power consumption.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Theory of Operation

The LM2734Z is a constant frequency PWM buck regulator IC that delivers a 1-A load current. The regulator has

a preset switching frequency of 3 MHz. This high frequency allows the LM2734Z to operate with small surface

mount capacitors and inductors, resulting in a DC–DC converter that requires a minimum amount of board

space. The LM2734Z is internally compensated, so it is simple to use, and requires few external components.

The LM2734Z uses current-mode control to regulate the output voltage.

The following operating description of the LM2734Z refers to the Functional Block Diagram and to the waveforms

in Figure 7. The LM2734Z supplies a regulated output voltage by switching the internal NMOS control switch at

constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the reset pulse

generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal

NMOS control switch. During this ON-time, the SW pin voltage (VSW) swings up to approximately VIN, and the

inductor current (IL) increases with a linear slope. ILis measured by the current-sense amplifier, which generates

an output proportional to the switch current. The sense signal is summed with the corrective ramp of the

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734

BOOST

GND

COUT

CBOOST

VOUT

CIN

VIN

VBOOST

VIN

TON

Inductor

Current

D = TON/TSW

VSW

TOFF

TSW

IPK

Voltage

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Feature Description (continued)

regulator and compared to the output of the error amplifier, which is proportional to the difference between the

feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the

next switching cycle begins. During the switch OFF-time, inductor current discharges through Schottky diode D1,

which forces the SW pin to swing below ground by the forward voltage (VD) of the catch diode. The regulator

loop adjusts the duty cycle (D) to maintain a constant output voltage.

Figure 7. LM2734Z Waveforms of SW Pin Voltage and Inductor Current

7.3.2 Boost Function

Capacitor CBOOST and diode D2 in Figure 8 are used to generate a voltage VBOOST. VBOOST - VSW is the gate drive

voltage to the internal NMOS control switch. To properly drive the internal NMOS switch during its ON-time,

VBOOST needs to be at least 1.6 V greater than VSW. Although the LM2734Z operates with this minimum voltage,

it may not have sufficient gate drive to supply large values of output current. Therefore, TI recommends that

VBOOST be greater than 2.5 V above VSW for best efficiency. VBOOST – VSW must not exceed the maximum

operating limit of 5.5 V.

5.5 V > VBOOST – VSW > 2.5 V for best performance.

Figure 8. VOUT Charges CBOOST

When the LM2734Z starts up, internal circuitry from the BOOST pin supplies a maximum of 20 mA to CBOOST.

This current charges CBOOST to a voltage sufficient to turn the switch on. The BOOST pin continues to source

current to CBOOST until the voltage at the feedback pin is greater than 0.76 V.

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VIN BOOST

GND

CBOOST

CIN

VIN

COUT

VOUT

VBOOST

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Feature Description (continued)

There are various methods to derive VBOOST:

1. From the input voltage (VIN)

2. From the output voltage (VOUT)

3. From an external distributed voltage rail (VEXT)

4. From a shunt or series zener diode

In Functional Block Diagram, capacitor CBOOST and diode D2 supply the gate-drive current for the NMOS switch.

Capacitor CBOOST is charged through diode D2 by VIN. During a normal switching cycle, when the internal NMOS

control switch is off (TOFF) (refer to Figure 7), VBOOST equals VIN minus the forward voltage of D2 (VFD2), during

which the current in the inductor (L) forward biases the Schottky diode D1 (VFD1). Therefore the voltage stored

across CBOOST is calculated using Equation 1.

VBOOST –VSW = VIN – VFD2 + VFD1 (1)

When the NMOS switch turns on (TON), the switch pin rises to:

VSW = VIN – (RDSON x IL), (2)

forcing VBOOST to rise thus reverse biasing D2. The voltage at VBOOST is then:

VBOOST = 2 VIN – (RDSON x IL) – VFD2 + VFD1 (3)

which is approximately:

2 VIN – 0.4 V (4)

for many applications. Thus the gate-drive voltage of the NMOS switch is approximately:

VIN –0.2 V (5)

An alternate method for charging CBOOST is to connect D2 to the output as shown in Figure 8. The output voltage

must be between 2.5 V and 5.5 V, so that proper gate voltage is applied to the internal switch. In this circuit,

CBOOST provides a gate drive voltage that is slightly less than VOUT.

In applications where both VIN and VOUT are greater than 5.5 V, or less than 3 V, CBOOST cannot be charged

directly from these voltages. If VIN and VOUT are greater than 5.5 V, CBOOST can be charged from VIN or VOUT

minus a Zener voltage by placing a Zener diode D3 in series with D2, as shown in Figure 9. When using a series

Zener diode from the input, ensure that the regulation of the input supply does not create a voltage that falls

outside the recommended VBOOST voltage.

(VINMAX – VD3) < 5.5V (6)

(VINMIN – VD3) > 1.6V (7)

Figure 9. Zener Reduces Boost Voltage from VIN

An alternative method is to place the Zener diode D3 in a shunt configuration as shown in Figure 10. A small

350-mW to 500-mW, 5.1-V Zener in a SOT or SOD package can be used for this purpose. A small ceramic

capacitor such as a 6.3-V, 0.1-µF capacitor (C4) must be placed in parallel with the Zener diode. When the

internal NMOS switch turns on, a pulse of current is drawn to charge the internal NMOS gate capacitance. The

0.1-µF parallel shunt capacitor ensures that the VBOOST voltage is maintained during this time.

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LM2734

VIN BOOST

GND

VBOOST

CBOOST

VIN

CIN

VOUT

COUT

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Feature Description (continued)

Resistor R3 must be chosen to provide enough RMS current to the Zener diode (D3) and to the BOOST pin. A

recommended choice for the Zener current (IZENER) is 1 mA. The current IBOOST into the BOOST pin supplies the

gate current of the NMOS control switch and varies typically according to Equation 8.

IBOOST = (D + 0.5) × (VZENER – VD2) mA

where

• D is the duty cycle

• VZENER and VD2 are in volts

• IBOOST is in milliamps

• VZENER is the voltage applied to the anode of the boost diode (D2)

• VD2 is the average forward voltage across D2 (8)

NOTE

Equation 8 for IBOOST gives typical current.

For the worst case IBOOST, increase the current by 25%. In that case, the worse-case boost current is:

IBOOST-MAX = 1.25 × IBOOST (9)

R3 is then given by Equation 10.

R3 = (VIN - VZENER) / (1.25 × IBOOST + IZENER) (10)

For example, let VIN = 10 V, VZENER =5V,VD2 = 0.7 V, IZENER = 1 mA, and duty cycle D = 50%. Then:

IBOOST = (0.5 + 0.5) × (5 - 0.7) mA = 4.3 mA (11)

R3 = (10 V - 5 V) / (1.25 × 4.3 mA + 1 mA) = 787 Ω(12)

Figure 10. Boost Voltage Supplied from the Shunt Zener on VIN

7.3.3 Soft-Start

This function forces VOUT to increase at a controlled rate during start-up. During soft-start, the reference voltage

of the error amplifier ramps from 0 V to its nominal value of 0.8 V in approximately 200 µs. This forces the

regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current.

7.3.4 Output Overvoltage Protection

The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal

reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control

switch is turned off, which allows the output voltage to decrease toward regulation.

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SNVS334F –JANUARY 2005–REVISED JANUARY 2016

Feature Description (continued)

7.3.5 Undervoltage Lockout

Undervoltage lockout (UVLO) prevents the LM2734Z from operating until the input voltage exceeds 2.74 V

(typical).

The UVLO threshold has approximately 440 mV of hysteresis, so the part operates until VIN drops below 2.3 V

(typical). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic.

7.3.6 Current Limit

The LM2734Z uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a

current limit comparator detects if the output switch current exceeds 1.7 A (typical), and turns off the switch until

the next switching cycle begins.

7.4 Device Functional Modes

7.4.1 Enable Pin and Shutdown Mode

The LM2734Z has a shutdown mode that is controlled by the enable pin (EN). When a logic low voltage is

applied to EN, the part is in shutdown mode and its quiescent current drops to typically 30 nA. Switch leakage

adds another 40 nA from the input supply. The voltage at this pin must never exceed VIN + 0.3 V.

7.4.2 Thermal Shutdown

Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature

exceeds 165°C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature

drops to approximately 150°C.

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LM2734

VIN VIN

BOOST

GND

VOUT

C3 L1

OFF

C1 R3

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

This device operates with wide input voltage in the range of 3 V to 20 V and provides regulated output voltage in

the range of 0.8 V to 18 V. This device is optimized for high-efficiency operation with a minimum number of

external components, making it ideal for applications where board space is constrained.

8.2 Typical Applications

8.2.1 LM2734Z Design Example 1

Figure 11. VBOOST Derived from VIN

Operating Conditions: 5 V to 1.5 V / 1 A

8.2.1.1 Design Requirements

Table 1 lists the operating conditions for the design example 1.

Table 1. Design Parameters

PARAMETER VALUE PARAMETER VALUE

VIN 5.0 V POUT 2.5 W

VOUT 2.5 V PDIODE 151 mW

IOUT 1.0 A PIND 75 mW

VD0.35 V PSWF 53 mW

Freq 3 MHz PSWR 53 mW

IQ1.5 mA PCOND 187 mW

TRISE 8 ns PQ7.5 mW

TFALL 8 ns PBOOST 21 mW

RDSON 330 mΩPLOSS 548 mW

INDDCR 75 mΩ

D 56.8%

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r = 'iL

D = VO + VD

VIN + VD - VSW

D = VO

VIN

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8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Inductor Selection

The Duty Cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN) as

shown in Equation 13.

(13)

The catch diode (D1) forward voltage drop and the voltage drop across the internal NMOS must be included to

calculate a more accurate duty cycle. Calculate D with Equation 14.

(14)

VSW can be approximated by Equation 15.

VSW = IOx RDS(ON) (15)

The diode forward drop (VD) can range from 0.3 V to 0.7 V depending on the quality of the diode. The lower VD

is, the higher the operating efficiency of the converter.

The inductor value determines the output ripple current. Lower inductor values decrease the size of the inductor,

but increase the output ripple current. An increase in the inductor value decreases the output ripple current. The

ratio of ripple current (ΔiL) to output current (IO) is optimized when it is set between 0.3 and 0.4 at 1 A. The ratio r

is defined in Equation 16.

(16)

One must also ensure that the minimum current limit (1.2 A) is not exceeded, so the peak current in the inductor

must be calculated. The peak current (ILPK) in the inductor is calculated by Equation 17.

ILPK = IO+ΔIL/2 (17)

If r = 0.5 at an output of 1 A, the peak current in the inductor is 1.25 A. The minimum specified current limit over

all operating conditions is 1.2 A. One can either reduce r to 0.4 resulting in a 1.2-A peak current, or make the

engineering judgement that 50 mA over is safe enough with a 1.7-A typical current limit and 6 sigma limits. When

the designed maximum output current is reduced, the ratio r can be increased. At a current of 0.1 A, r can be

made as high as 0.9. The ripple ratio can be increased at lighter loads because the net ripple is actually quite

low, and if r remains constant the inductor value can be made quite large. An equation empirically developed for

the maximum ripple ratio at any current below 2 A is:

r = 0.387 × IOUT-0.3667 (18)

NOTE

Use this as a guideline.

The LM2734Z operates at frequencies allowing the use of ceramic output capacitors without compromising

transient response. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple.

See the Output Capacitor section for more details on calculating output voltage ripple.

Product Folder Links: LM2734Z LM2734Z-Q1

'VO = 'iL x (RESR + 1

8 x fS x CO)

IRMS-IN = IO x D x r2

1-D +

L = VO + VD

IO x r x fSx (1-D)

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Now that the ripple current or ripple ratio is determined, the inductance is calculated by Equation 19.

where

• fsis the switching frequency

• IOis the output current (19)

When selecting an inductor, make sure that it is capable of supporting the peak output current without saturating.

Inductor saturation results in a sudden reduction in inductance and prevent the regulator from operating correctly.

Because of the speed of the internal current limit, the peak current of the inductor need only be specified for the

required maximum output current. For example, if the designed maximum output current is 0.5 A and the peak

current is 0.7 A, then the inductor must be specified with a saturation current limit of >0.7 A. There is no need to

specify the saturation or peak current of the inductor at the 1.7-A typical switch current limit. The difference in

inductor size is a factor of 5. Because of the operating frequency of the LM2734Z, ferrite based inductors are

preferred to minimize core losses. This presents little restriction because the variety of ferrite based inductors is

huge. Lastly, inductors with lower series resistance (DCR) provides better operating efficiency. For

recommended inductors, see the design examples in Typical Applications.

8.2.1.2.2 Input Capacitor

An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The

primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and ESL (Equivalent

Series Inductance). The recommended input capacitance is 10 µF, although 4.7 µF works well for input voltages

below 6 V. The input voltage rating is specifically stated by the capacitor manufacturer. Make sure to check any

recommended deratings and also verify if there is any significant change in capacitance at the operating input

voltage and the operating temperature. The input capacitor maximum RMS input current rating (IRMS-IN) must be

greater than:

(20)

As seen in Equation 20, the maximum RMS capacitor current occurs when D = 0.5. Always calculate the RMS at

the point where the duty cycle, D, is closest to 0.5. The ESL of an input capacitor is usually determined by the

effective cross sectional area of the current path. A large leaded capacitor has high ESL and a 0805 ceramic

chip capacitor has very low ESL. At the operating frequencies of the LM2734Z, certain capacitors may have an

ESL so large that the resulting impedance (2πfL) is higher than that required to provide stable operation. As a

result, surface mount capacitors are strongly recommended. Sanyo POSCAP, Tantalum or Niobium, Panasonic

SP or Cornell Dubilier ESR, and multilayer ceramic capacitors (MLCC) are all good choices for both input and

output capacitors and have very low ESL. For MLCCs, TI recommends using X7R or X5R dielectrics. Consult

capacitor manufacturer data sheet to see how rated capacitance varies over operating conditions.

8.2.1.2.3 Output Capacitor

The output capacitor is selected based upon the desired output ripple and transient response. The initial current

of a load transient is provided mainly by the output capacitor. The output ripple of the converter is shown in

Equation 21.

(21)

When using MLCCs, the ESR is typically so low that the capacitive ripple may dominate. When this occurs, the

output ripple is approximately sinusoidal and 90° phase shifted from the switching action. Given the availability

and quality of MLCCs and the expected output voltage of designs using the LM2734Z, there is really no need to

review any other capacitor technologies. Another benefit of ceramic capacitors is their ability to bypass high

frequency noise. A certain amount of switching edge noise couples through parasitic capacitances in the inductor

Product Folder Links: LM2734Z LM2734Z-Q1

D = VOUT + VD

VIN + VD - VSW

K = POUT

POUT + PLOSS

K = POUT

R1 =VO- 1

VREF x R2

IRMS-OUT = IO x r

LM2734Z

LM2734Z-Q1

www.ti.com

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

to the output. A ceramic capacitor bypasses this noise while a tantalum will not. Because the output capacitor is

one of the two external components that control the stability of the regulator control loop, most applications will

require a minimum at 10 µF of output capacitance. Capacitance can be increased significantly with little detriment

to the regulator stability. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R.

Again, verify actual capacitance at the desired operating voltage and temperature.

Check the RMS current rating of the capacitor. The RMS current rating of the capacitor chosen must also meet

Equation 22.

(22)

8.2.1.2.4 Catch Diode

The catch diode (D1) conducts during the switch OFF-time. A Schottky diode is recommended for its fast

switching times and low forward voltage drop. The catch diode must be chosen so that its current rating is

greater than Equation 23.

ID1 = IOx (1-D) (23)

The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin.

To improve efficiency choose a Schottky diode with a low forward voltage drop.

8.2.1.2.5 Boost Diode

A standard diode such as the 1N4148 type is recommended. For VBOOST circuits derived from voltages less than

3.3 V, a small-signal Schottky diode is recommended for greater efficiency. A good choice is the BAT54 small

signal diode.

8.2.1.2.6 Boost Capacitor

A ceramic 0.01-µF capacitor with a voltage rating of at least 6.3 V is sufficient. The X7R and X5R MLCCs

provide the best performance.

8.2.1.2.7 Output Voltage

The output voltage is set using Equation 24 where R2 is connected between the FB pin and GND, and R1 is

connected between VOand the FB pin. A good value for R2 is 10 kΩ.

(24)

8.2.1.2.8 Calculating Efficiency, and Junction Temperature

The complete LM2734Z DC–DC converter efficiency can be calculated in the following manner:

(25)

(26)

Calculations for determining the most significant power losses are shown below. Other losses totaling less than

2% are not discussed.

Power loss (PLOSS) is the sum of two basic types of losses in the converter, switching and conduction.

Conduction losses usually dominate at higher output loads, where as switching losses remain relatively fixed and

dominate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D).

(27)

Product Folder Links: LM2734Z LM2734Z-Q1

6PCOND + PSW + PDIODE + PIND + PQ + PBOOST = PLOSS

D = VO + VD + VDCR

VIN + VD - VSW

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

VSW is the voltage drop across the internal NFET when it is on, and is equal to Equation 28.

VSW = IOUT × RDSON (28)

VDis the forward voltage drop across the Schottky diode. It can be obtained from the Electrical Characteristics

section. If the voltage drop across the inductor (VDCR) is accounted for, use Equation 29 to calculate the duty

cycle.

(29)

This usually gives only a minor duty cycle change, and has been omitted in the examples for simplicity.

The conduction losses in the free-wheeling Schottky diode are calculated using Equation 30.

PDIODE = VD× IOUT(1-D) (30)

Often this is the single most significant power loss in the circuit. Take care choosing a Schottky diode that has a

low forward voltage drop.

Another significant external power loss is the conduction loss in the output inductor. The equation can be

simplified to Equation 31.

PIND = IOUT2× RDCR (31)

The LM2734Z conduction loss is mainly associated with the internal NFET, as shown in Equation 32.

PCOND = IOUT2×RDSON x D (32)

Switching losses are also associated with the internal NFET. They occur during the switch on and off transition

periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss

is to empirically measure the rise and fall times (10% to 90%) of the switch at the switch node using Equation 33

through Equation 35.

PSWF = 1/2 (VIN × IOUT × freq × TFALL) (33)

PSWR = 1/2(VIN x IOUT x freq x TRISE) (34)

PSW = PSWF + PSWR (35)

Table 2. Typical Rise and Fall Times vs Input Voltage

VIN TRISE TFALL

5 V 8 ns 4 ns

10 V 9 ns 6 ns

15 V 10 ns 7 ns

Another loss is the power required for operation of the internal circuitry:

PQ= IQx VIN (36)

IQis the quiescent operating current, and is typically around 1.5 mA. The other operating power that needs to be

calculated is that required to drive the internal NFET:

PBOOST = IBOOST x VBOOST (37)

VBOOST is normally between 3 VDC and 5 VDC. The IBOOST rms current is approximately 4.25 mA. Total power

losses are:

(38)

8.2.1.2.9 Calculating the LM2734Z Junction Temperature

Thermal Definitions:

TJ= Chip junction temperature

TA= Ambient temperature

RθJC = Thermal resistance from chip junction to device case

RθJA = Thermal resistance from chip junction to ambient air

Product Folder Links: LM2734Z LM2734Z-Q1

RTJA = TJ - TC

Power

RTJA = TJ - TA

Power

RT = 'T

Power

LM2734Z

LM2734Z-Q1

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SNVS334F –JANUARY 2005–REVISED JANUARY 2016

Figure 12. Cross-Sectional View of Integrated Circuit Mounted on a Printed Circuit Board

Heat in the LM2734Z due to internal power dissipation is removed through conduction and/or convection.

Conduction: Heat transfer occurs through cross sectional areas of material. Depending on the material, the

transfer of heat can be considered to have poor to good thermal conductivity properties (insulator vs conductor).

Heat Transfer goes as:

silicon→package→lead frame→PCB.

Convection: Heat transfer is by means of airflow. This could be from a fan or natural convection. Natural

convection occurs when air currents rise from the hot device to cooler air.

Thermal impedance is defined as shown in Equation 39.

(39)

Thermal impedance from the silicon junction to the ambient air is defined as shown in Equation 40.

(40)

This impedance can vary depending on the thermal properties of the PCB. This includes PCB size, weight of

copper used to route traces and ground plane, and number of layers within the PCB. The type and number of

thermal vias can also make a large difference in the thermal impedance. Thermal vias are necessary in most

applications. They conduct heat from the surface of the PCB to the ground plane. Four to six thermal vias must

be placed under the exposed pad to the ground plane if the WSON package is used. If the 6-pin SOT package is

used, place two to four thermal vias close to the ground pin of the device.

The data sheet specifies two different RθJA numbers for the thin SOT–6 package. The two numbers show the

difference in thermal impedance for a four-layer board with 2-oz. copper traces, versus a four-layer board with 1-

oz. copper. RθJA equals 120°C/W for 2-oz. copper traces and GND plane, and 235°C/W for 1-oz. copper traces

and GND plane.

The first method to accurately measure the silicon temperature for a given application, two methods can be used.

The first method requires the user to know the thermal impedance of the silicon junction to case. (RθJC) is

approximately 80°C/W for the thin SOT-6 package. Knowing the internal dissipation from the efficiency

calculation given previously, and the case temperature, which can be empirically measured on the bench:

(41)

Therefore:

TJ= (RθJC × PLOSS)+TC(42)

Product Folder Links: LM2734Z LM2734Z-Q1

RTJA = 165oC - 94oC

322 mW = 220oC/W

6PCOND + PSWF + PSWR + PQ + PBOOST = PINTERNAL

PINTERNAL = 322 mW

RTJA = 165oC - TA

PINTERNAL

6PCOND + PSWF + PSWR + PQ + PBOOST = PINTERNAL

PINTERNAL = 322 mW

TJ = (RTJC x Power) + TC = 80oC/W x 322 mW + TC

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

(43)

The second method can give a very accurate silicon junction temperature. The first step is to determine RθJA of

the application. The LM2734Z has overtemperature protection circuitry. When the silicon temperature reaches

165°C, the device stops switching. The protection circuitry has a hysteresis of 15°C. Once the silicon

temperature has decreased to approximately 150°C, the device starts to switch again. Knowing this, the RθJA for

any PCB can be characterized during the early stages of the design by raising the ambient temperature in the

given application until the circuit enters thermal shutdown. If the SW-pin is monitored, it is obvious when the

internal NFET stops switching indicating a junction temperature of 165°C. Knowing the internal power dissipation

from the above methods, the junction temperature and the ambient temperature, RθJA can be determined using

Equation 44.

(44)

Once this is determined, the maximum ambient temperature allowed for a desired junction temperature can be

found using Equation 45.

(45)

Using a standard Texas Instruments 6-pin SOT demonstration board to determine the RθJA of the board. The four

layer PCB is constructed using FR4 with 1/2-oz copper traces. The copper ground plane is on the bottom layer.

The ground plane is accessed by two vias. The board measures 2.5 cm × 3 cm. It was placed in an oven with no

forced airflow.

The ambient temperature was raised to 94°C, and at that temperature, the device went into thermal shutdown.

(46)

If the junction temperature was to be kept below 125°C, then the ambient temperature cannot go above 54.2°C.

TJ- (RθJA × PLOSS)=TA(47)

The method described above to find the junction temperature in the thin 6-pin SOT package can also be used to

calculate the junction temperature in the WSON package. The 6-pin WSON package has a RθJC = 20°C/W, and

RθJA can vary depending on the application. RθJA can be calculated in the same manner as described in method

2 (see LM2734Z Design Example 3).

8.2.1.2.10 WSON Package

The LM2734Z is packaged in a thin, 6-pin SOT package and the 6-pin WSON. The WSON package has the

same footprint as the thin, 6-pin SOT, but is thermally superior due to the exposed ground paddle on the bottom

of the package.

Figure 13. No Pullback WSON Configuration

Product Folder Links: LM2734Z LM2734Z-Q1

RTJAa = 165oC - 113oC

322 mW = 161oC/W

6PCOND + PSWF + PSWR + PQ + PBOOST = PINTERNAL

PINTERNAL = 322 mW

4SW

VIN

BOOST

GND

LM2734Z

LM2734Z-Q1

www.ti.com

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

RθJA of the WSON package is normally two to three times better than that of the thin, 6-pin SOT package for a

similar PCB configuration (area, copper weight, thermal vias).

Figure 14. Dog Bone

For certain high power applications, the PCB land may be modified to a dog bone shape (see Figure 14). By

increasing the size of ground plane, and adding thermal vias, the RθJA for the application can be reduced.

(48)

This example follows LM2734Z Design Example 2, but uses the WSON package. Using a standard Texas

Instruments 6-pin WSON demonstration board, use Method 2 to determine RθJA of the board. The four-layer PCB

is constructed using FR4 with 1- or 2-oz copper traces. The copper ground plane is on the bottom layer. The

ground plane is accessed by four vias. The board measures 2.5 cm × 3 cm. It was placed in an oven with no

forced airflow.

The ambient temperature was raised to 113°C, and at that temperature, the device went into thermal shutdown.

(49)

If the junction temperature is to be kept below 125°C, then the ambient temperature cannot go above 73.2°C.

TJ- (RθJA × PLOSS)=TA(50)

8.2.1.2.11 Package Selection

To determine which package you must use for your specific application, variables must be known before

determining the appropriate package to use.

1. Maximum ambient system temperature

2. Internal LM2734Z power losses

3. Maximum junction temperature desired

4. RθJA of the specific application, or RθJC (WSON or 6-pin SOT)

The junction temperature must be less than 125°C for the worst-case scenario.

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

Table 3 lists the bill of materials for LM2734Z design example 1.

Table 3. Bill of Materials for Figure 11

PART ID PART VALUE PART NUMBER MANUFACTURER

U1 1-A Buck Regulator LM2734ZX Texas Instruments

C1, Input Cap 10 µF, 6.3 V, X5R C3216X5ROJ106M TDK

C2, Output Cap 10 µF, 6.3 V, X5R C3216X5ROJ106M TDK

C3, Boost Cap 0.01 uF, 16 V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.3 VFSchottky 1A, 10VR MBRM110L ON Semi

D2, Boost Diode 1 VFat 50-mA Diode 1N4148W Diodes, Inc.

L1 2.2 µH, 1.8 A ME3220–222MX Coilcraft

R1 8.87 kΩ, 1% CRCW06038871F Vishay

R2 10.2 kΩ, 1% CRCW06031022F Vishay

R3 100 kΩ, 1% CRCW06031003F Vishay

8.2.1.3 Application Curve

VIN=5.0 V VOUT = 1.5 V No load

Figure 15. Typical Start-Up Profile

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734

VIN

BOOST

GND

VOUT

C3 L1

OFF

VIN

C1 R3

LM2734Z

LM2734Z-Q1

www.ti.com

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

8.2.2 LM2734Z Design Example 2

Figure 16. VBOOST Derived from VOUT

12Vto3.3V/1A

8.2.2.1 Design Requirements

Table 4 lists the operating conditions for design example 2.

Table 4. Design Parameters

PARAMETER VALUE PARAMETER VALUE

VIN 5.0 V POUT 2.5 W

VOUT 2.5 V PDIODE 151 mW

IOUT 1.0 A PIND 75 mW

VD0.35 V PSWF 53 mW

Freq 3 MHz PSWR 53 mW

IQ1.5 mA PCOND 187 mW

TRISE 8 ns PQ7.5 mW

TFALL 8 ns PBOOST 21 mW

RDSON 330 mΩPLOSS 548 mW

INDDCR 75 mΩ

D 56.8%

8.2.2.2 Detailed Design Procedure

Refer to Detailed Design Procedure.Table 5 lists the bill of materials for LM2734Z design example 2.

Table 5. Bill of Materials for Figure 16

PART ID PART VALUE PART NUMBER MANUFACTURER

U1 1-A Buck Regulator LM2734ZX Texas Instruments

C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK

C2, Output Cap 22 µF, 6.3 V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01 µF, 16 V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.34 VFSchottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 0.6 VFat 30-mA Diode BAT17 Vishay

L1 3.3 µH, 1.3 A ME3220–332MX Coilcraft

R1 31.6 kΩ, 1% CRCW06033162F Vishay

R2 10.0 kΩ, 1% CRCW06031002F Vishay

R3 100 kΩ, 1% CRCW06031003F Vishay

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734

VIN VIN

BOOST

GND

VOUT

C3 L1

OFF

C1 R3

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

8.2.3 LM2734Z Design Example 3

Figure 17. VBOOST Derived from VSHUNT

18Vto1.5V/1A

8.2.3.1 Design Requirements

Table 6 lists the operating conditions for design example 3.

Table 6. Design Parameters

PARAMETER VALUE PARAMETER VALUE

Package SOT-6 POUT 2.475 W

VIN 12.0 V PDIODE 523 mW

VOUT 3.30 V PIND 56.25 mW

IOUT 750 mA PSWF 108 mW

VD0.35 V PSWR 108 mW

Freq 3 MHz PCOND 68.2 mW

IQ1.5 mA PQ18 mW

IBOOST 4 mA PBOOST 20 mW

VBOOST 5 V PLOSS 902 mW

TRISE 8 ns

TFALL 8 ns

RDSON 400 mΩ

INDDCR 75 mΩ

D 30.3%

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734

VIN VIN

BOOST

GND

VOUT

C3 L1

OFF

C1 R3

LM2734Z

LM2734Z-Q1

www.ti.com

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

8.2.3.2 Detailed Design Procedure

Refer to Detailed Design Procedure.

Table 7 lists the bill of materials for LM2734Z design example 3.

Table 7. Bill of Materials for Figure 17

PART ID PART VALUE PART NUMBER MANUFACTURER

U1 1-A Buck Regulator LM2734ZX Texas Instruments

C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK

C2, Output Cap 22 µF, 6.3 V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01 µF, 16 V, X7R C1005X7R1C103K TDK

C4, Shunt Cap 0.1 µF, 6.3 V, X5R C1005X5R0J104K TDK

D1, Catch Diode 0.4 VFSchottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1 VFat 50-mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 5.1 V 250-Mw SOT BZX84C5V1 Vishay

L1 3.3 µH, 1.3 A ME3220–332MX Coilcraft

R1 8.87 kΩ, 1% CRCW06038871F Vishay

R2 10.2 kΩ, 1% CRCW06031022F Vishay

R3 100 kΩ, 1% CRCW06031003F Vishay

R4 4.12 kΩ, 1% CRCW06034121F Vishay

8.2.4 LM2734Z Design Example 4

Figure 18. VBOOST Derived from Series Zener Diode (VIN)

15Vto1.5V/1A

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

8.2.4.1 Design Requirements

Table 8 lists the operating conditions for design example 4.

Table 8. Design Parameters

PARAMETER VALUE PARAMETER VALUE

Package WSON-6 POUT 2.475 W

VIN 12.0 V PDIODE 523 mW

VOUT 3.3 V PIND 56.25 mW

IOUT 750 mA PSWF 108 mW

VD0.35 V PSWR 108 mW

Freq 3 MHz PCOND 68.2 mW

IQ1.5 mA PQ18 mW

IBOOST 4 mA PBOOST 20 mW

VBOOST 5 V PLOSS 902 mW

TRISE 8 ns

TFALL 8 ns

RDSON 400 mΩ

INDDCR 75 mΩ

D 30.3%

8.2.4.2 Detailed Design Procedure

Refer to Detailed Design Procedure.

Table 9 lists the bill of materials for LM2734Z design example 4.

Table 9. Bill of Materials for Figure 18

PART ID PART VALUE PART NUMBER MANUFACTURER

U1 1-A Buck Regulator LM2734ZX Texas Instruments

C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK

C2, Output Cap 22 µF, 6.3 V, X5R C3216X5ROJ226M TDK

C3, Boost Cap 0.01 µF, 16 V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.4 VFSchottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1 VFat 50-mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 11 V 350-Mw SOT BZX84C11T Diodes, Inc.

L1 3.3 µH, 1.3 A ME3220–332MX Coilcraft

R1 8.87 kΩ, 1% CRCW06038871F Vishay

R2 10.2 kΩ, 1% CRCW06031022F Vishay

R3 100 kΩ, 1% CRCW06031003F Vishay

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734

VIN VIN

BOOST

GND

VOUT

C3 L1

OFF

D2 D3

C1 R3

LM2734Z

LM2734Z-Q1

www.ti.com

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

8.2.5 LM2734Z Design Example 5

Figure 19. VBOOST Derived from Series Zener Diode (VOUT)

15Vto9V/1A

8.2.5.1 Design Requirements

Table 10 lists the operating conditions for design example 5.

Table 10. Design Parameters

PARAMETER VALUE PARAMETER VALUE

Package WSON-6

VIN 15.0 V POUT 9 W

VOUT 9.0 V PDIODE 130 mW

IOUT 1.0 A PIND 104 mW

VD0.35 V PCOND 186 mW

Freq 3 MHz PSW 382.5 mW

IQ1.5 mA PQ22.5 mW

TRISE 10 ns PLOSS 825 mW

TFALL 7 ns

RDSON 300 mΩ

INDDCR 104 mΩ

D 62%

8.2.5.2 Detailed Design Procedure

Refer to Detailed Design Procedure.

Table 11 lists the bill of materials for the LM2734Z design example 5.

Table 11. Bill of Materials for Figure 19

PART ID PART VALUE PART NUMBER MANUFACTURER

U1 1-A Buck Regulator LM2734ZX Texas Instruments

C1, Input Cap 10 µF, 25 V, X7R C3225X7R1E106M TDK

C2, Output Cap 22 µF, 16 V, X5R C3216X5R1C226M TDK

C3, Boost Cap 0.01 µF, 16 V, X7R C1005X7R1C103K TDK

D1, Catch Diode 0.4 VFSchottky 1A, 30VR SS1P3L Vishay

D2, Boost Diode 1 VFat 50-mA Diode 1N4148W Diodes, Inc.

D3, Zener Diode 4.3 V 350-mw SOT BZX84C4V3 Diodes, Inc.

L1 2.2 µH, 1.8 A ME3220–222MX Coilcraft

R1 102 kΩ, 1% CRCW06031023F Vishay

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

Table 11. Bill of Materials for Figure 19 (continued)

PART ID PART VALUE PART NUMBER MANUFACTURER

R2 10.2 kΩ, 1% CRCW06031022F Vishay

R3 100 kΩ, 1% CRCW06031003F Vishay

9 Power Supply Recommendations

The LM2734Z is designed to operate from an input voltage supply range between 3 to 20 V. This input supply

must be able to withstand the maximum input current and maintain voltage above 3.0 V. In case where input

supply is located farther away (more than a few inches) from LM2734Z additional bulk capacitance may be

required in addition to ceramic bypass capacitors.

10 Layout

10.1 Layout Guidelines

When planning layout there are a few things to consider when trying to achieve a clean, regulated output. The

most important consideration when completing the layout is the close coupling of the GND connections of the CIN

capacitor and the catch diode D1. These ground ends must be close to one another and be connected to the

GND plane with at least two through-holes. Place these components as close to the IC as possible. Next in

importance is the location of the GND connection of the COUT capacitor, which must be near the GND

connections of CIN and D1.

There must be a continuous ground plane on the bottom layer of a two-layer board except under the switching

node island.

The FB pin is a high impedance node and care must be taken to make the FB trace short to avoid noise pickup

and inaccurate regulation. The feedback resistors must be placed as close as possible to the IC, with the GND of

R2 placed as close as possible to the GND of the IC. The VOUT trace to R1 must be routed away from the

inductor and any other traces that are switching.

High AC currents flow through the VIN, SW and VOUT traces, so they must be as short and wide as possible.

However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated

noise can be decreased by choosing a shielded inductor.

The remaining components must also be placed as close as possible to the IC. Please see the AN-1229 SIMPLE

SWITCHER® PCB Layout Guidelines Application Note (SNVA054) for further considerations and the LM2734Z

demo board as an example of a four-layer layout.

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734Z

LM2734Z-Q1

www.ti.com

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

10.2 Layout Examples

Figure 20. Top Layer Figure 21. Bottom Layer

Figure 22. Internal Plane 1 (GND) Figure 23. Internal Plane 2 (VIN)

Product Folder Links: LM2734Z LM2734Z-Q1

LM2734Z

LM2734Z-Q1

SNVS334F –JANUARY 2005–REVISED JANUARY 2016

www.ti.com

11 Device and Documentation Support

11.1 Device Support

11.1.1 Third-Party Products Disclaimer

TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT

CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES

OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER

ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.

11.2 Documentation Support

11.2.1 Related Documentation

For related documentation see the following:

•AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines Application Note (SNVA054)

•AN-1350 LM2734 Evaluation Board User's Guide (SNVA100)

11.3 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective

contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of

Use.

TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration

among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help

solve problems with fellow engineers.

Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and

contact information for technical support.

11.4 Trademarks

WEBENCH, E2E are trademarks of Texas Instruments.

All other trademarks are the property of their respective owners.

11.5 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

11.6 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

Product Folder Links: LM2734Z LM2734Z-Q1

PACKAGE OPTION ADDENDUM

www.ti.com 28-Feb-2017

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM2734ZMK/NOPB ACTIVE SOT-23-THIN DDC 6 1000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SFTB

LM2734ZMKX/NOPB ACTIVE SOT-23-THIN DDC 6 3000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SFTB

LM2734ZQMKE/NOPB ACTIVE SOT-23-THIN DDC 6 250 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SVBB

LM2734ZQSDE/NOPB ACTIVE WSON NGG 6 250 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 L238B

LM2734ZSD/NOPB ACTIVE WSON NGG 6 1000 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 L163B

LM2734ZSDX/NOPB ACTIVE WSON NGG 6 4500 Green (RoHS

& no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 L163B

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability

information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that

lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between

the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight

in homogeneous material)

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

PACKAGE OPTION ADDENDUM

www.ti.com 28-Feb-2017

Addendum-Page 2

(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish

value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

OTHER QUALIFIED VERSIONS OF LM2734Z, LM2734Z-Q1 :

•Catalog: LM2734Z

•Automotive: LM2734Z-Q1

NOTE: Qualified Version Definitions:

•Catalog - TI's standard catalog product

•Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM2734ZMK/NOPB SOT-

23-THIN DDC 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

LM2734ZMKX/NOPB SOT-

23-THIN DDC 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

LM2734ZQMKE/NOPB SOT-

23-THIN DDC 6 250 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

LM2734ZQSDE/NOPB WSON NGG 6 250 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1

LM2734ZSD/NOPB WSON NGG 6 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1

LM2734ZSDX/NOPB WSON NGG 6 4500 330.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 3-Mar-2017

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM2734ZMK/NOPB SOT-23-THIN DDC 6 1000 210.0 185.0 35.0

LM2734ZMKX/NOPB SOT-23-THIN DDC 6 3000 210.0 185.0 35.0

LM2734ZQMKE/NOPB SOT-23-THIN DDC 6 250 210.0 185.0 35.0

LM2734ZQSDE/NOPB WSON NGG 6 250 210.0 185.0 35.0

LM2734ZSD/NOPB WSON NGG 6 1000 210.0 185.0 35.0

LM2734ZSDX/NOPB WSON NGG 6 4500 367.0 367.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 3-Mar-2017

Pack Materials-Page 2

MECHANICAL DATA

NGG0006A

www.ti.com

SDE06A (Rev A)

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Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Texas Instruments:

LM2734ZQMK/NOPB LM2734ZQMKE/NOPB LM2734ZQMKX/NOPB LM2734ZQSD/NOPB LM2734ZQSDE/NOPB

LM2734ZQSDX/NOPB