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LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
LM2736 Thin SOT 750 mA Load Step-Down DC-DC Regulator
1 Features 3 Description
The LM2736 regulator is a monolithic, high frequency,
1• Thin SOT-6 Package PWM step-down DC/DC converter in a 6-pin Thin
• 3.0 V to 18 V Input Voltage Range SOT package. It provides all the active functions to
• 1.25 V to 16 V Output Voltage Range provide local DC/DC conversion with fast transient
response and accurate regulation in the smallest
• 750 mA Output Current possible PCB area.
• 550 kHz (LM2736Y) and 1.6 MHz (LM2736X)
Switching Frequencies With a minimum of external components and online
design support through WEBENCH®, the LM2736 is
• 350 mΩNMOS Switch easy to use. The ability to drive 750 mA loads with an
• 30 nA Shutdown Current internal 350 mΩNMOS switch using state-of-the-art
• 1.25 V, 2% Internal Voltage Reference 0.5 µm BiCMOS technology results in the best power
density available. The world class control circuitry
• Internal Soft-Start allows for on-times as low as 13 ns, thus supporting
• Current-Mode, PWM Operation exceptionally high frequency conversion over the
• WEBENCH®Online Design Tool entire 3 V to 18 V input operating range down to the
minimum output voltage of 1.25 V. Switching
• Thermal Shutdown frequency is internally set to 550 kHz (LM2736Y) or
1.6 MHz (LM2736X), allowing the use of extremely
2 Applications small surface mount inductors and chip capacitors.
• Local Point of Load Regulation Even though the operating frequencies are very high,
• Core Power in HDDs efficiencies up to 90% are easy to achieve. External
shutdown is included, featuring an ultra-low stand-by
• Set-Top Boxes current of 30 nA. The LM2736 utilizes current-mode
• Battery Powered Devices control and internal compensation to provide high-
• USB Powered Devices performance regulation over a wide range of
operating conditions. Additional features include
• DSL Modems internal soft-start circuitry to reduce inrush current,
• Notebook Computers pulse-by-pulse current limit, thermal shutdown, and
output over-voltage protection.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LM2736 SOT (6) 2.90 mm x 1.60 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Typical Application Circuit Efficiency vs. Load Current "X"
VIN =5V,VOUT = 3.3 V
1
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.
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
Table of Contents
7.4 Device Functional Modes........................................ 10
1 Features.................................................................. 18 Application and Implementation ........................ 11
2 Applications ........................................................... 18.1 Application Information .......................................... 11
3 Description............................................................. 18.2 Typical Applications ............................................... 13
4 Revision History..................................................... 29 Power Supply Recommendations...................... 27
5 Pin Configuration and Functions......................... 310 Layout................................................................... 27
6 Specifications......................................................... 410.1 Layout Guidelines ................................................. 27
6.1 Absolute Maximum Ratings ...................................... 410.2 Layout Example .................................................... 28
6.2 ESD Ratings ............................................................ 411 Device and Documentation Support................. 29
6.3 Recommended Operating Conditions....................... 411.1 Device Support...................................................... 29
6.4 Thermal Information.................................................. 411.2 Documentation Support ........................................ 29
6.5 Electrical Characteristics........................................... 511.3 Trademarks........................................................... 29
6.6 Typical Characteristics.............................................. 611.4 Electrostatic Discharge Caution............................ 29
7 Detailed Description.............................................. 811.5 Glossary................................................................ 29
7.1 Overview................................................................... 812 Mechanical, Packaging, and Orderable
7.2 Functional Block Diagram......................................... 9Information........................................................... 29
7.3 Feature Description................................................... 9
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision G (October 2014) to Revision H Page
• Updated Design Requirements and moved Bill of Materials to Detailed Design Procedures.............................................. 13
Changes from Revision F (April 2013) to Revision G Page
• Added ESD Ratings table, Feature Description section, Device Functional Modes,Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section.................................................................................................. 4
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1
2
3
6
5
4
BOOST
GND
FB
SW
VIN
EN
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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
5 Pin Configuration and Functions
Package DDC (R-PDSO-G6)
6-Lead SOT
Top View
Pin Functions
PIN I/O DESCRIPTION
NAME NO.
Boost voltage that drives the internal NMOS control switch. A bootstrap capacitor is
BOOST 1 I connected between the BOOST and SW pins.
Signal and Power ground pin. Place the bottom resistor of the feedback network as close as
GND 2 GND possible to this pin for accurate regulation.
FB 3 I Feedback pin. Connect FB to the external resistor divider to set output voltage.
Enable control input. Logic high enables operation. Do not allow this pin to float or be greater
EN 4 I than VIN + 0.3 V.
VIN 5 I Input supply voltage. Connect a bypass capacitor to this pin.
SW 6 O Output switch. Connects to the inductor, catch diode, and bootstrap capacitor.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)
MIN MAX UNIT
VIN -0.5 22 V
SW Voltage -0.5 22 V
Boost Voltage -0.5 28 V
Boost to SW Voltage -0.5 8 V
FB Voltage -0.5 3 V
EN Voltage -0.5 VIN + 0.3 V
Junction Temperature 150 °C
Infrared/Convection Reflow (15sec) 220 °C
Soldering
Information Wave Soldering Lead temperature (10sec) 260 °C
Tstg Storage temperature -65 150 °C
(1) 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),
V(ESD) Electrostatic discharge ±2000 V
per ANSI/ESDA/JEDEC JS-001, all pins(1)
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) MIN NOM MAX UNIT
VIN 3 18 V
SW Voltage -0.5 18 V
Boost Voltage -0.5 23 V
Boost to SW Voltage 1.6 5.5 V
Junction Temperature Range −40 125 °C
6.4 Thermal Information LM2736
THERMAL METRIC(1) DDC UNIT
6 PINS
RθJA(2) Junction-to-ambient thermal resistance 158.1
RθJC(top) Junction-to-case (top) thermal resistance 46.5
RθJB Junction-to-board thermal resistance 29.5 °C/W
ψJT Junction-to-top characterization parameter 0.8
ψJB Junction-to-board characterization parameter 29.2
RθJC(bot) Junction-to-case (bottom) thermal resistance n/a
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
(2) Thermal shutdown will occur if the junction temperature exceeds 165°C. The maximum power dissipation is a function of TJ(MAX) ,θJA
and TA. The maximum allowable power dissipation at any ambient temperature is PD= (TJ(MAX) – TA)/θJA . All numbers apply for
packages soldered directly onto a 3” x 3” PC board with 2oz. copper on 4 layers in still air. For a 2 layer board using 1 oz. copper in still
air, θJA = 204°C/W.
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6.5 Electrical Characteristics
Specifications with standard typeface are for TJ= 25°C unless otherwise specified. Datasheet min/max specification limits are
ensured by design, test, or statistical analysis. TJ= 25°C TJ = -40°C to 125°C
PARAMETER TEST CONDITIONS UNIT
MIN(1) TYP(2) MAX(1) MIN TYP MAX
VFB Feedback Voltage 1.250 1.225 1.275 V
ΔVFB/ΔFeedback Voltage Line VIN = 3V to 18V 0.01 % / V
VIN Regulation
Feedback Input Bias
IFB Sink/Source 10 250 nA
Current
Undervoltage Lockout VIN Rising 2.74 2.90
UVLO Undervoltage Lockout VIN Falling 2.3 2.0 V
UVLO Hysteresis 0.44 0.30 0.62
LM2736X 1.6 1.2 1.9
FSW Switching Frequency MHz
LM2736Y 0.55 0.40 0.66
LM2736X 92% 85%
DMAX Maximum Duty Cycle LM2736Y 96% 90%
LM2736X 2%
DMIN Minimum Duty Cycle LM2736Y 1%
RDS(ON) Switch ON Resistance VBOOST - VSW = 3V 350 650 mΩ
ICL Switch Current Limit VBOOST - VSW = 3V 1.5 1.0 2.3 A
IQQuiescent Current Switching 1.5 2.5 mA
Quiescent Current VEN = 0V 30 nA
(shutdown) LM2736X (50% Duty 2.2 3.3
Cycle)
IBOOST Boost Pin Current mA
LM2736Y (50% Duty 0.9 1.6
Cycle)
Shutdown Threshold VEN Falling 0.4
Voltage
VEN_TH V
Enable Threshold VEN Rising 1.8
Voltage
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
All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified
otherwise.
Figure 1. Oscillator Frequency vs Temperature - "X" Figure 2. Oscillator Frequency vs Temperature - "Y"
Figure 3. Current Limit vs Temperature Figure 4. VFB vs Temperature
Figure 5. RDSON vs Temperature Figure 6. IQSwitching vs Temperature
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Typical Characteristics (continued)
All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified
otherwise.
Figure 7. Line Regulation - "X" Figure 8. Line Regulation - "Y"
VOUT = 3.3 V, IOUT = 500 mA VOUT = 3.3 V, IOUT = 500 mA
Figure 9. Line Regulation - "X" Figure 10. Line Regulation - "Y"
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0
0
VIN
VD
TON
t
t
Inductor
Current
D = TON/TSW
VSW
TOFF
TSW
IL
IPK
SW
Voltage
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
7 Detailed Description
7.1 Overview
The LM2736 device is a constant frequency PWM buck regulator IC that delivers a 750 mA load current. The
regulator has a preset switching frequency of either 550 kHz (LM2736Y) or 1.6 MHz (LM2736X). These high
frequencies allow the LM2736 device to operate with small surface mount capacitors and inductors, resulting in
DC/DC converters that require a minimum amount of board space. The LM2736 device is internally
compensated, so it is simple to use, and requires few external components. The LM2736 device uses current-
mode control to regulate the output voltage.
The following operating description of the LM2736 device will refer to the Simplified Block Diagram (Functional
Block Diagram) and to the waveforms in Figure 11. The LM2736 device 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 regulator’s corrective ramp and compared to the error amplifier’s output, 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 11. LM2736 Waveforms of SW Pin Voltage and Inductor Current
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L
R1
R2
D
1
D2
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
SW
EN
FB
GND
Error Amplifier -
+VREF
1.25V
COUT
ON
OFF
VBOOST
VSW
+
-
CBOOST
VOUT
CIN
VIN
VIN
ISENSE
+
-
+
-
+
-1.375V
OVP
Comparator
Error
Signal
-
+
IL
LM2736
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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 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.
7.3.2 Undervoltage Lockout
Undervoltage lockout (UVLO) prevents the LM2736 device from operating until the input voltage exceeds 2.74 V
(typ).
The UVLO threshold has approximately 440mV of hysteresis, so the part will operate until VIN drops below 2.3 V
(typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic.
7.3.3 Current Limit
The LM2736 device 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 1.5 A (typ), and turns off the switch until
the next switching cycle begins.
7.3.4 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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7.4 Device Functional Modes
7.4.1 Enable Pin / Shutdown Mode
The LM2736 device 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 should never exceed VIN + 0.3 V.
7.4.2 Soft-Start
This function forces VOUT to increase at a controlled rate during start up. During soft-start, the error amplifier’s
reference voltage ramps from 0 V to its nominal value of 1.25 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.
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BOOST
SW
GND
L
D1
D2
COUT
CBOOST
VOUT
CIN
VIN
VIN
VBOOST
LM2736
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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
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
8.1.1 Boost Function
Capacitor CBOOST and diode D2 in Figure 12 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 LM2736 device will operate with this minimum
voltage, it may not have sufficient gate drive to supply large values of output current. Therefore, it is
recommended that VBOOST be greater than 2.5 V above VSW for best efficiency. VBOOST – VSW should not exceed
the maximum operating limit of 5.5 V.
5.5 V > VBOOST – VSW > 2.5 V for best performance.
Figure 12. VOUT Charges CBOOST
When the LM2736 device 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 will continue to
source current to CBOOST until the voltage at the feedback pin is greater than 1.18 V.
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 the Functional Block Diagram, capacitor CBOOST and diode D2 supply the gate-drive current for the NMOS
switch. Capacitor CBOOST is charged via diode D2 by VIN. During a normal switching cycle, when the internal
NMOS control switch is off (TOFF) (refer to Figure 11), 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
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 = 2VIN – (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
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VIN BOOST
SW
GND
CBOOST
L
D1
D2
D3
VBOOST
VIN
CIN
COUT
VOUT
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Application Information (continued)
VIN - 0.2 V (5)
An alternate method for charging CBOOST is to connect D2 to the output as shown in Figure 12. The output
voltage should be between 2.5 V and 5.5 V, so that proper gate voltage will be 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 13. When using a
series zener diode from the input, ensure that the regulation of the input supply doesn’t create a voltage that falls
outside the recommended VBOOST voltage.
(VINMAX – VD3) < 5.5 V (6)
(VINMIN – VD3) > 1.6 V (7)
Figure 13. Zener Reduces Boost Voltage from VIN
An alternative method is to place the zener diode D3 in a shunt configuration as shown in Figure 14. 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) should 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.
Resistor R3 should 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 the following formula for the X -
version:
IBOOST = 0.49 x (D + 0.54) x (VZENER – VD2) mA (8)
IBOOST can be calculated for the Y version using the following:
IBOOST = 0.20 x (D + 0.54) x (VZENER - VD2) µA (9)
where D is the duty cycle, VZENER and VD2 are in volts, and IBOOST is in milliamps. VZENER is the voltage applied to
the anode of the boost diode (D2), and VD2 is the average forward voltage across D2. Note that this formula for
IBOOST gives typical current. For the worst case IBOOST, increase the current by 40%. In that case, the worst case
boost current will be
IBOOST-MAX = 1.4 x IBOOST (10)
R3 will then be given by
R3 = (VIN - VZENER) / (1.4 x IBOOST + IZENER) (11)
For example, using the X-version let VIN = 10 V, VZENER =5V,VD2 = 0.7 V, IZENER = 1 mA, and duty cycle D =
50%. Then
IBOOST = 0.49 x (0.5 + 0.54) x (5 - 0.7) mA = 2.19mA (12)
R3 = (10 V - 5 V) / (1.4 x 2.19 mA + 1 mA) = 1.23 kΩ(13)
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VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
C1 R3
VIN BOOST
SW
GND
L
D1
D2
D3
R3
C4
VBOOST
CBOOST
VZ
VIN
CIN
COUT
VOUT
LM2736
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Application Information (continued)
Figure 14. Boost Voltage Supplied from the Shunt Zener on VIN
8.2 Typical Applications
8.2.1 LM2736X (1.6 MHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA
Figure 15. LM2736X (1.6 MHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA
8.2.1.1 Design Requirements
Derive charge for VBOOST from the input supply (VIN). VBOOST – VSW should not exceed the maximum operating
limit of 5.5 V.
8.2.1.2 Detailed Design Procedures
Table 1. Bill of Materials for Figure 15
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750 mA Buck Regulator LM2736X TI
C1, Input Cap 10-µF, 6.3V, X5R C3216X5ROJ106M TDK
C2, Output Cap 10-µF, 6.3V, X5R C3216X5ROJ106M TDK
C3, Boost Cap 0.01-uF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.3 VFSchottky 1 A, 10 VR MBRM110L ON Semi
D2, Boost Diode 1 VF@ 50 mA Diode 1N4148W Diodes, Inc.
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L = VO + VD
IO x r x fSx (1-D)
r = 'iL
lO
D = VO + VD
VIN + VD - VSW
D = VO
VIN
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Typical Applications (continued)
Table 1. Bill of Materials for Figure 15 (continued)
PART ID PART VALUE PART NUMBER MANUFACTURER
L1 4.7-µH, 1.7 A, VLCF4020T- 4R7N1R2 TDK
R1 2 kΩ, 1% CRCW06032001F Vishay
R2 10 kΩ, 1% CRCW06031002F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay
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 14:
(14)
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. Use Equation 15 to Calculate D.
(15)
VSW can be approximated by:
VSW = IOx RDS(ON) (16)
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 will decrease 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 750 mA.
The ratio r is defined in .
(17)
One must also ensure that the minimum current limit (1.0 A) is not exceeded, so the peak current in the inductor
must be calculated. Use Equation 18 to calculate the peak current (ILPK) in the inductor.
ILPK = IO+ΔIL/2 (18)
If r = 0.7 at an output of 750 mA, the peak current in the inductor will be 1.0125 A. The minimum ensured current
limit over all operating conditions is 1.0 A. One can either reduce r to 0.6 resulting in a 975 mA peak current, or
make the engineering judgement that 12.5 mA over will be safe enough with a 1.5 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. Equation 19 is
empirically developed for the maximum ripple ratio at any current below 2 A.
r = 0.387 x IOUT-0.3667 (19)
Note that this is just a guideline.
The LM2736 device 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.
Now that the ripple current or ripple ratio is determined, the inductance is calculated using Equation 20
(20)
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IRMS-OUT = IO x r
12
'VO = 'iL x (RESR + 1
8 x fS x CO)
IRMS-IN = IO x D x r2
12
1-D +
LM2736
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SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
where fsis the switching frequency and IOis the output current. When selecting an inductor, make sure that it is
capable of supporting the peak output current without saturating. Inductor saturation will result 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 should
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 1.5 A typical switch current limit. The difference in inductor size is a factor of 5. Because of the
operating frequency of the LM2736, ferrite based inductors are preferred to minimize core losses. This presents
little restriction since the variety of ferrite based inductors is huge. Lastly, inductors with lower series resistance
(DCR) will provide better operating efficiency. For recommended inductors see Example Circuits.
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:
(21)
It can be shown from the above equation that 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 will have high ESL
and a 0805 ceramic chip capacitor will have very low ESL. At the operating frequencies of the LM2736, certain
capacitors may have an ESL so large that the resulting impedance (2πfL) will be 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 it is recommended to use
X7R or X5R dielectrics. Consult capacitor manufacturer datasheet 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:
(22)
When using MLCCs, the ESR is typically so low that the capacitive ripple may dominate. When this occurs, the
output ripple will be 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 LM2736, 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 will couple through parasitic capacitances in the
inductor to the output. A ceramic capacitor will bypass this noise while a tantalum will not. Since 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
the following condition:
(23)
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LM2736
R1 =VO- 1
VREF x R2
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
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 should be chosen so that its current rating is greater than:
ID1 = IOx (1-D) (24)
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 16 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 the following equation 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.
(25)
8.2.1.3 Application Curves
VOUT = 5 V VOUT = 5 V
Figure 16. Efficiency vs Load Current - "X" Figure 17. Efficiency vs Load Current - "Y"
16 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated
Product Folder Links: LM2736
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
VOUT = 3.3 V VOUT = 3.3 V
Figure 18. Efficiency vs Load Current - "X" Figure 19. Efficiency vs Load Current - "Y"
VOUT = 1.5 V VOUT = 1.5 V
Figure 20. Efficiency vs Load Current - "X" Figure 21. Efficiency vs Load Current - "Y"
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: LM2736
VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
VIN
C1 R3
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
8.2.2 LM2736X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA
Figure 22. LM2736X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA
8.2.2.1 Design Requirements
Derive charge for VBOOST from the output voltage, (VOUT). The output voltage should be between 2.5V and 5.5V.
8.2.2.2 Detailed Design Procedures
Table 2. Bill of Materials for Figure 22
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736X TI
C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK
C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.34VFSchottky 1A, 30VR SS1P3L Vishay
D2, Boost Diode 30V, 200 mA Schottky BAT54 Diodes Inc.
L1 4.7µH, 1.7A, VLCF4020T- 4R7N1R2 TDK
R1 16.5kΩ, 1% CRCW06031652F Vishay
R2 10.0 kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
Please refer to Detailed Design Procedures.
8.2.2.3 Application Curves
Please refer to Application Curves
18 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
D3
C4
R4
C1 R3
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
8.2.3 LM2736X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA
Figure 23. LM2736X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA
8.2.3.1 Design Requirements
An alternative method when VIN is greater than 5.5V is to place the zener diode D3 in a shunt configuration. 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) should 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
8.2.3.2 Detailed Design Procedure
Table 3. Bill of Materials for Figure 23
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736X TI
C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK
C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
C4, Shunt Cap 0.1µF, 6.3V, X5R C1005X5R0J104K TDK
D1, Catch Diode 0.4VFSchottky 1A, 30VR SS1P3L Vishay
D2, Boost Diode 1VF@ 50mA Diode 1N4148W Diodes, Inc.
D3, Zener Diode 5.1V 250Mw SOT BZX84C5V1 Vishay
L1 6.8µH, 1.6A, SLF7032T-6R8M1R6 TDK
R1 2kΩ, 1% CRCW06032001F Vishay
R2 10kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
R4 4.12kΩ, 1% CRCW06034121F Vishay
Please refer to Detailed Design Procedures.
8.2.3.3 Application Curves
Please refer to Application Curves.
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
ON
OFF
D2D3
C1 R3
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
8.2.4 LM2736X (1.6 MHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA
Figure 24. LM2736X (1.6 MHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA
8.2.4.1 Design Requirements
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 is greater than 5.5 V, CBOOST can be charged from VIN minus a zener voltage
by placing a zener diode D3 in series with D2. When using a series zener diode from the input, ensure that the
regulation of the input supply doesn’t create a voltage that falls outside the recommended VBOOST voltage.
(VINMAX – VD3) < 5.5 V (26)
(VINMIN – VD3) > 1.6 V (27)
8.2.4.2 Detailed Design Procedure
Table 4. Bill of Materials for Figure 24
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750 mA Buck Regulator LM2736X TI
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 1 A, 30VR SS1P3L Vishay
D2, Boost Diode 1VF@ 50 mA Diode 1N4148W Diodes, Inc.
D3, Zener Diode 11 V 350 Mw SOT BZX84C11T Diodes, Inc.
L1 6.8µH, 1.6 A, SLF7032T-6R8M1R6 TDK
R1 2 kΩ, 1% CRCW06032001F Vishay
R2 10 kΩ, 1% CRCW06031002F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay
Please refer to Detailed Design Procedures.
8.2.4.3 Application Curves
Please refer to Application Curves
20 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
ON
OFF
D2 D3
C1 R3
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
8.2.5 LM2736X (1.6 MHz) VBOOST Derived from Series Zener Diode (VOUT)15Vto9V/750mA
Figure 25.
8.2.5.1 Design Requirements
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 VOUT minus a
zener voltage by placing a zener diode D3 in series with D2.
8.2.5.2 Detailed Design Procedure
Table 5. Bill of Materials for Figure 25
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736X TI
C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK
C2, Output Cap 22µF, 16V, X5R C3216X5R1C226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.4VFSchottky 1A, 30VR SS1P3L Vishay
D2, Boost Diode 1VF@ 50mA Diode 1N4148W Diodes, Inc.
D3, Zener Diode 4.3V 350mw SOT BZX84C4V3 Diodes, Inc.
L1 6.8µH, 1.6A, SLF7032T-6R8M1R6 TDK
R1 61.9kΩ, 1% CRCW06036192F Vishay
R2 10kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
Please refer to Detailed Design Procedures.
8.2.5.3 Application Curves
Please refer to Application Curves
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
C1 R3
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
8.2.6 LM2736Y (550 kHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA
Figure 26. LM2736Y (550 kHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA
8.2.6.1 Design Requirements
Derive charge for VBOOST from the input voltage, (VIN). VBOOST should be greater than 2.5 V above VSW for best
efficiency. VBOOST – VSW should not exceed the maximum operating limit of 5.5 V.
8.2.6.2 Detailed Design Procedure
Table 6. Bill of Materials for Figure 26
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736Y TI
C1, Input Cap 10µF, 6.3V, X5R C3216X5ROJ106M TDK
C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.3VFSchottky 1A, 10VR MBRM110L ON Semi
D2, Boost Diode 1VF@ 50mA Diode 1N4148W Diodes, Inc.
L1 10µH, 1.6A, SLF7032T-100M1R4 TDK
R1 2kΩ, 1% CRCW06032001F Vishay
R2 10kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
Please refer toDetailed Design Procedures.
8.2.6.3 Application Curves
Please refer to Application Curves.
22 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated
Product Folder Links: LM2736
VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
VIN
C1 R3
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
8.2.7 LM2736Y (550 kHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA
Figure 27. LM2736Y (550 kHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA
8.2.7.1 Design Requirements
Derive charge for VBOOST from the output voltage, (VOUT). The output voltage should be between 2.5V and 5.5V.
8.2.7.2 Detailed Design Procedure
Table 7. Bill of Materials for Figure 27
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736Y TI
C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK
C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.34VFSchottky 1A, 30VR SS1P3L Vishay
D2, Boost Diode 30V, 200 mA Schottky BAT54 Diodes Inc.
L1 10µH, 1.6A, SLF7032T-100M1R4 TDK
R1 16.5kΩ, 1% CRCW06031652F Vishay
R2 10.0 kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
Please refer to Detailed Design Procedures.
8.2.7.3 Application Curves
Please refer to Application Curves.
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
D2
ON
OFF
D3
C4
R4
C1 R3
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
8.2.8 LM2736Y (550 kHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA
Figure 28. LM2736Y (550 kHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA
8.2.8.1 Design Requirements
An alternative method when VIN is greater than 5.5V is to place the zener diode D3 in a shunt configuration. 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) should 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.
8.2.8.2 Detailed Design Procedure
Table 8. Bill of Materials for Figure 28
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736Y TI
C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK
C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
C4, Shunt Cap 0.1µF, 6.3V, X5R C1005X5R0J104K TDK
D1, Catch Diode 0.4VFSchottky 1A, 30VR SS1P3L Vishay
D2, Boost Diode 1VF@ 50mA Diode 1N4148W Diodes, Inc.
D3, Zener Diode 5.1V 250Mw SOT BZX84C5V1 Vishay
L1 15µH, 1.5A SLF7045T-150M1R5 TDK
R1 2kΩ, 1% CRCW06032001F Vishay
R2 10kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
R4 4.12kΩ, 1% CRCW06034121F Vishay
Please refer to Detailed Design Procedures.
8.2.8.3 Application Curves
Please refer to Application Curves.
24 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
ON
OFF
D2D3
C1 R3
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
8.2.9 LM2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA
Figure 29. M2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA
8.2.9.1 Design Requirements
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 is greater than 5.5 V, CBOOST can be charged from VIN minus a zener voltage
by placing a zener diode D3 in series with D2. When using a series zener diode from the input, ensure that the
regulation of the input supply doesn’t create a voltage that falls outside the recommended VBOOST voltage.
(VINMAX – VD3) < 5.5 V (28)
(VINMIN – VD3) > 1.6 V (29)
8.2.9.2 Detailed Design Procedure
Table 9. Bill of Materials for Figure 29
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750mA Buck Regulator LM2736Y TI
C1, Input Cap 10µF, 25V, X7R C3225X7R1E106M TDK
C2, Output Cap 22µF, 6.3V, X5R C3216X5ROJ226M TDK
C3, Boost Cap 0.01µF, 16V, X7R C1005X7R1C103K TDK
D1, Catch Diode 0.4VFSchottky 1A, 30VR SS1P3L Vishay
D2, Boost Diode 1VF@ 50mA Diode 1N4148W Diodes, Inc.
D3, Zener Diode 11V 350Mw SOT BZX84C11T Diodes, Inc.
L1 15µH, 1.5A, SLF7045T-150M1R5 TDK
R1 2kΩ, 1% CRCW06032001F Vishay
R2 10kΩ, 1% CRCW06031002F Vishay
R3 100kΩ, 1% CRCW06031003F Vishay
Please refer to Detailed Design Procedures.
8.2.9.3 Application Curves
Please refer to Application Curves.
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Links: LM2736
VIN VIN
EN
BOOST
SW
FB
GND
VOUT
C3 L1
C2
R1
R2
D1
ON
OFF
D2 D3
C1 R3
LM2736
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
www.ti.com
8.2.10 LM2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VOUT)15Vto9V/750mA
Figure 30. LM2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VOUT)15Vto9V/750mA
8.2.10.1 Design Requirements
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 VOUT minus a
zener voltage by placing a zener diode D3 in series with D2.
8.2.10.2 Detailed Design Procedure
Table 10. Bill of Materials for Figure 30
PART ID PART VALUE PART NUMBER MANUFACTURER
U1 750 mA Buck Regulator LM2736Y TI
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 1 A, 30 VR SS1P3L Vishay
D2, Boost Diode 1 VF@ 50 mA Diode 1N4148W Diodes, Inc.
D3, Zener Diode 4.3 V 350 mw SOT BZX84C4V3 Diodes, Inc.
L1 22 µH, 1.4 A, SLF7045T-220M1R3-1PF TDK
R1 61.9 kΩ, 1% CRCW06036192F Vishay
R2 10 kΩ, 1% CRCW06031002F Vishay
R3 100 kΩ, 1% CRCW06031003F Vishay
Please refer to Detailed Design Procedures.
8.2.10.3 Application Curves
Please refer to Application Curves.
26 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated
Product Folder Links: LM2736
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
9 Power Supply Recommendations
Input voltage is rated as 3 V to 18 V however care should be taken in certain circuit configurations eg. VBOOST
derived from VIN where the requirement that VBOOST - VSW < 5.5 V should be observed. Also for best efficiency
VBOOST should be at least 2.5 V above VSW.
The voltage on the Enable pin should not exceed VIN by more than 0.3 V.
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 should 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 should be near the GND
connections of CIN and D1.
There should 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 should be taken to make the FB trace short to avoid noise pickup
and inaccurate regulation. The feedback resistors should 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 should 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 should 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 should also be placed as close as possible to the IC. Please see Application Note
AN-1229 SNVA054 for further considerations and the LM2736 device demo board as an example of a four-layer
layout.
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 27
Product Folder Links: LM2736
LM2736
www.ti.com
SNVS316H –SEPTEMBER 2004–REVISED DECEMBER 2014
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 SNVA054
11.3 Trademarks
WEBENCH, SIMPLE SWITCHER are registered trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
11.4 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.
11.5 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.
Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Links: LM2736
PACKAGE OPTION ADDENDUM
www.ti.com 6-Feb-2020
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
LM2736XMK NRND SOT-23-THIN DDC 6 1000 TBD Call TI Call TI -40 to 125 SHAB
LM2736XMK/NOPB ACTIVE SOT-23-THIN DDC 6 1000 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHAB
LM2736XMKX/NOPB ACTIVE SOT-23-THIN DDC 6 3000 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHAB
LM2736YMK NRND SOT-23-THIN DDC 6 1000 TBD Call TI Call TI -40 to 125 SHBB
LM2736YMK/NOPB ACTIVE SOT-23-THIN DDC 6 1000 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHBB
LM2736YMKX/NOPB ACTIVE SOT-23-THIN DDC 6 3000 Green (RoHS
& no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHBB
(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) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(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.
(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.
PACKAGE OPTION ADDENDUM
www.ti.com 6-Feb-2020
Addendum-Page 2
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.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM2736XMK SOT-
23-THIN DDC 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2736XMK/NOPB SOT-
23-THIN DDC 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2736XMKX/NOPB SOT-
23-THIN DDC 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2736YMK SOT-
23-THIN DDC 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2736YMK/NOPB SOT-
23-THIN DDC 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
LM2736YMKX/NOPB SOT-
23-THIN DDC 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
PACKAGE MATERIALS INFORMATION
www.ti.com 29-Sep-2019
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2736XMK SOT-23-THIN DDC 6 1000 210.0 185.0 35.0
LM2736XMK/NOPB SOT-23-THIN DDC 6 1000 210.0 185.0 35.0
LM2736XMKX/NOPB SOT-23-THIN DDC 6 3000 210.0 185.0 35.0
LM2736YMK SOT-23-THIN DDC 6 1000 210.0 185.0 35.0
LM2736YMK/NOPB SOT-23-THIN DDC 6 1000 210.0 185.0 35.0
LM2736YMKX/NOPB SOT-23-THIN DDC 6 3000 210.0 185.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 29-Sep-2019
Pack Materials-Page 2
www.ti.com
PACKAGE OUTLINE
C
TYP
0.20
0.12
0.25
3.05
2.55
4X 0.95
1.1 MAX
TYP
0.1
0.0
6X 0.5
0.3
TYP
0.6
0.3
1.9
TYP-80
A
3.05
2.75
B
1.75
1.45
SOT - 1.1 max heightDDC0006A
SOT
4214841/A 08/2016
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. Reference JEDEC MO-193.
34
0.2 C A B
16
INDEX AREA
PIN 1
GAGE PLANE
SEATING PLANE
0.1 C
SCALE 4.000
www.ti.com
EXAMPLE BOARD LAYOUT
0.07 MAX
ARROUND 0.07 MIN
ARROUND
6X (1.1)
6X (0.6)
(2.7)
4X (0.95)
(R0.05) TYP
4214841/A 08/2016
SOT - 1.1 max heightDDC0006A
SOT
NOTES: (continued)
4. Publication IPC-7351 may have alternate designs.
5. Solder mask tolerances between and around signal pads can vary based on board fabrication site.
SYMM
LAND PATTERN EXAMPLE
EXPLOSED METAL SHOWN
SCALE:15X
SYMM
1
34
6
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
SOLDER MASK
DEFINED
EXPOSED METAL
METAL
SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
SOLDERMASK DETAILS
EXPOSED METAL
www.ti.com
EXAMPLE STENCIL DESIGN
(2.7)
4X(0.95)
6X (1.1)
6X (0.6)
(R0.05) TYP
SOT - 1.1 max heightDDC0006A
SOT
4214841/A 08/2016
NOTES: (continued)
6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
7. Board assembly site may have different recommendations for stencil design.
SOLDER PASTE EXAMPLE
BASED ON 0.125 THICK STENCIL
SCALE:15X
SYMM
SYMM
1
34
6
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