LM22678TJE-ADJ/NOPB - NATIONAL SEMICONDUCTOR

LM22678/-Q1 42-V, 5-A SIMPLE SWITCHER® Step-Down Voltage Regulator

With Easy-to-Use Package

1 Features

• New product available: LM61460 3-V to 36-V, 6-A

low EMI synchronous converter

• Wide input voltage range: 4.5 V to 42 V

• Internally compensated voltage mode control

• Stable with low-ESR ceramic capacitors

• 100-mΩ N-channel MOSFET

• Output voltage options:

-ADJ (outputs as low as 1.285 V)

-5.0 (output fixed to 5 V)

• ±1.5% Feedback reference accuracy

• Switching frequency of 500 kHz

• –40°C to 125°C Operating junction temperature

range

• Precision enable pin

• Integrated bootstrap diode

• Integrated soft start

• Fully WEBENCH® enabled

• LM22678-Q1 is an automotive-grade product

that is AEC-Q100 grade 1 qualified (–40°C to

+125°C operating junction temperature)

• PFM (exposed pad) package

2 Applications

•Industrial distributed power applications

•Test and measurement

•Appliances

•General-purpose wide VIN applications

3 Description

The LM22678 switching regulator provides all of the

functions necessary to implement an efficient high-

voltage step-down (buck) regulator using a minimum

of external components. This easy-to-use regulator

incorporates a 42-V N-channel MOSFET switch that

can provide up to 5 A of load current. Excellent line

and load regulation along with high efficiency (> 90%)

are featured. Voltage mode control offers short

minimum on-time, allowing the widest ratio between

input and output voltages. Internal loop compensation

means that the user is free from the tedious task of

calculating the loop compensation components. Fixed

5-V output and adjustable output voltage options are

available. A switching frequency of 500 kHz allows for

small external components and good transient

response. A precision enable input allows

simplification of regulator control and system power

sequencing. In shutdown mode the regulator draws

only 25 µA (typical). Built-in soft-start (500 µs, typical)

saves external components. The LM22678 device

also has built-in thermal shutdown, and current

limiting to protect against accidental overloads.

The new product, LM61460, offers higher efficiency,

lower stand-by quiescent current, and improved EMI

performance. See the device comparison table to

compare.Start WEBENCH design with LM61460

The LM22678 device is a member of Texas

Instruments' SIMPLE SWITCHER® family. The

SIMPLE SWITCHER concept provides for an easy-to-

use complete design using a minimum number of

external components and the TI WEBENCH design

tool. TI's WEBENCH tool includes features such as

external component calculation, electrical simulation,

thermal simulation, and Build-It boards for easy

design-in.

Device Information

PART NUMBER PACKAGE(1) BODY SIZE (NOM)

LM22678 TO-263 (7) 10.16 mm x 9.85 mm

LM22678-Q1

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

the end of the data sheet.

LM22678-ADJ

VIN

BOOT

GND

VIN

VOUT

Simplified Application Schematic

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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.

Table of Contents

1 Features............................................................................1

2 Applications..................................................................... 1

3 Description.......................................................................1

4 Revision History.............................................................. 2

5 Pin Configuration and Functions...................................3

6 Specifications.................................................................. 4

6.1 Absolute Maximum Ratings........................................ 4

6.2 Handling Ratings: LM22678........................................4

6.3 Handling Ratings: LM22678-Q1..................................4

6.4 Recommended Operating Conditions.........................4

6.5 Thermal Information....................................................4

6.6 Electrical Characteristics.............................................5

6.7 Typical Characteristics................................................6

7 Detailed Description........................................................8

7.1 Overview..................................................................... 8

7.2 Functional Block Diagram........................................... 8

7.3 Feature Description.....................................................9

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

8 Application and Implementation.................................. 14

8.1 Application Information............................................. 14

8.2 Typical Applications.................................................. 15

9 Layout.............................................................................20

9.1 Layout Guidelines..................................................... 20

9.2 Layout Example........................................................ 21

9.3 Thermal Considerations............................................21

10 Device and Documentation Support..........................22

10.1 Documentation Support.......................................... 22

10.2 Support Resources................................................. 22

10.3 Receiving Notification of Documentation Updates..22

10.4 Electrostatic Discharge Caution..............................22

10.5 Glossary..................................................................22

4 Revision History

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

Changes from Revision L (November 2014) to Revision M (October 2020) Page

• Added LM61460 bullet to the Features ..............................................................................................................1

• Updated the numbering format for tables, figures and cross-references throughout the document...................1

• Changed title from LM22678/-Q1 42-V, 5-A SIMPLE SWITCHER® Step-Down Voltage Regulator With

Features to LM22678/-Q1 42-V, 5-A SIMPLE SWITCHER® Step-Down Voltage Regulator With Easy to Use

Package .............................................................................................................................................................1

Changes from Revision K (March 2013) to Revision L (November 2014) Page

• Added Pin Configuration and Functions section, Handling Rating 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 ............................................................................................................................................................... 1

• Deleted Inverting Regulator Application .......................................................................................................... 14

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5 Pin Configuration and Functions

Exposed Pad

Connect to GND

5 NC

6 FB

3 BOOT

1 SW

2 VIN

4 GND

7 EN

Figure 5-1. 7-Pin PFM Package (Top View)

Table 5-1. Pin Functions

PIN TYPE DESCRIPTION APPLICATION INFORMATION

NAME NO.

BOOT 3 I Bootstrap input Provides the gate voltage for the high-side NFET.

EN 7 I Enable input Used to control regulator start-up and shutdown. See Section 7.3.1.

EP EP — Exposed pad Connect to ground. Provides thermal connection to PCB. See Section 8.

FB 6 I Feedback input Feedback input to the regulator

GND 4 — Ground input to regulator;

system common System ground pin

NC 5 — Not connected Pin is not electrically connected inside chip. Pin does function as

thermal conductor.

SW 1 O Switch pin Switching output of regulator

VIN 2 I Input voltage Supply input to the regulator

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6 Specifications

6.1 Absolute Maximum Ratings

MIN MAX UNIT(1) (2)

VIN to GND 43 V

EN Pin Voltage –0.5 6 V

SW to GND (3) -5 VIN V

BOOT Pin Voltage VSW + 7 V

FB Pin Voltage –0.5 7 V

Power Dissipation Internally Limited

Junction Temperature(4) 150 °C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of

device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or

other conditions beyond those indicated in the Section 6.4 is not implied. The Recommended Operating Conditions indicate conditions

at which the device is functional and should not be operated beyond such conditions.

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

specifications.

(3) The absolute-maximum specification of the ‘SW to GND’ applies to dc voltage. An extended negative voltage limit of –10 V applies to a

pulse of up to 50 ns.

(4) For soldering specifications, refer to the application report Absolute Maximum Ratings for Soldering (SNOA549).

6.2 Handling Ratings: LM22678

MIN MAX UNIT

Tstg Storage temperature range –65 150 °C

V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all

pins(1) –2 2 kV

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

6.3 Handling Ratings: LM22678-Q1

MIN MAX UNIT

Tstg Storage temperature range –65 150 °C

V(ESD) Electrostatic discharge Human body model (HBM), per AEC Q100-002(1) –2 2 kV

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

6.4 Recommended Operating Conditions

MIN MAX UNIT

VIN Supply Voltage 4.5 42 V

Junction Temperature Range –40 125 °C

6.5 Thermal Information

THERMAL METRIC(1) (2)

LM22678,

LM22678-Q1

UNIT

NDR

7 PINS

RθJA Junction-to-ambient thermal resistance 22 °C/W

(1) For more information about traditional and new thermal metrics, see the application report IC Package Thermal Metrics (SPRA953).

(2) The value of RθJA for the PFM package of 22°C/W is valid if package is mounted to 1 square inch of copper. The RθJA value can range

from 20 to 30°C/W depending on the amount of PCB copper dedicated to heat transfer. See application note AN-1797 (SNVA328) for

more information.

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6.6 Electrical Characteristics

Typical values represent the most likely parametric norm at TA = TJ = 25°C, and are provided for reference purposes only.

Unless otherwise specified: VIN = 12 V.

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

LM22678-5.0

VFB Feedback Voltage VIN = 8 V to 42 V 4.925 5.0 5.075 V

VIN = 8 V to 42 V, –40°C ≤ TJ ≤ 125°C 4.9 5.1

LM22678-ADJ

VFB Feedback Voltage VIN = 4.7 V to 42 V 1.266 1.285 1.304 V

VIN = 4.7 V to 42 V, –40°C ≤ TJ ≤ 125°C 1.259 1.311

ALL OUTPUT VOLTAGE VERSIONS

IQQuiescent Current VFB = 5 V 3.4 mA

VFB = 5 V, –40°C ≤ TJ ≤ 125°C 6

ISTDBY Standby Quiescent Current EN Pin = 0 V 25 40 µA

ICL Current Limit 6.0 7.1 8.4 A

–40°C ≤ TJ ≤ 125°C 5.75 8.75

ILOutput Leakage Current VIN = 42 V, EN Pin = 0 V, VSW = 0 V 0.2 2 µA

VSW = –1 V 0.1 3 µA

RDS(ON) Switch On-Resistance 0.1 0.14 Ω

–40°C ≤ TJ ≤ 125°C 0.2

fOOscillator Frequency 500 kHz

–40°C ≤ TJ ≤ 125°C 400 600

TOFFMIN Minimum Off-time 200 ns

–40°C ≤ TJ ≤ 125°C 100 300

TONMIN Minimum On-time 100 ns

IBIAS Feedback Bias Current VFB = 1.3 V (ADJ Version Only) 230 nA

VEN Enable Threshold Voltage Falling 1.6 V

Falling, –40°C ≤ TJ ≤ 125°C 1.3 1.9

VENHYST Enable Threshold Hysteresis 0.6 V

IEN Enable Input Current EN Input = 0 V 6 µA

TSD Thermal Shutdown Threshold 150 °C

(1) MIN and MAX limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation

using Statistical Quality Control (SQC) methods. Limits are used to calculate TI's Average Outgoing Quality Level (AOQL).

(2) Typical values represent most likely parametric norms at the conditions specified and are not ensured.

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6.7 Typical Characteristics

Vin = 12 V, TJ = 25°C (unless otherwise specified)

Figure 6-1. Efficiency vs IOUT and VIN, VOUT = 3.3 V Figure 6-2. Normalized Switching Frequency vs

Temperature

Figure 6-3. Current Limit vs Temperature Figure 6-4. Normalized RDS(ON) vs Temperature

Figure 6-5. Feedback Bias Current vs Temperature Figure 6-6. Normalized Enable Threshold Voltage

vs Temperature

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Figure 6-7. Standby Quiescent Current vs Input

Voltage

Figure 6-8. Normalized Feedback Voltage vs

Temperature

Figure 6-9. Normalized Feedback Voltage vs Input Voltage

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7 Detailed Description

7.1 Overview

The LM22678 incorporates a voltage mode constant frequency PWM architecture. In addition, input voltage

feedforward is used to stabilize the loop gain against variations in input voltage. This allows the loop

compensation to be optimized for transient performance. The power MOSFET, in conjunction with the diode,

produces a rectangular waveform at the switch pin, which swings from about zero volts to VIN. The inductor and

output capacitor average this waveform to become the regulator output voltage. By adjusting the duty cycle of

this waveform, the output voltage can be controlled. The error amplifier compares the output voltage with the

internal reference and adjusts the duty cycle to regulate the output at the desired value.

The internal loop compensation of the -ADJ option is optimized for outputs of 5 V and below. If an output voltage

of 5 V or greater is required, the -5.0 option can be used with an external voltage divider. The minimum output

voltage is equal to the reference voltage, that is, 1.285 V (typ).

7.2 Functional Block Diagram

LOGIC

OSC

TYPE III

COMP

1.285V

Soft-start

INT REG, EN,UVLO

GND

BOOT

VIN

VOUT

Error Amp.

PWM Cmp.

Vcc

ILimit

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7.3 Feature Description

7.3.1 Precision Enable and UVLO

The precision enable input (EN) is used to control the regulator. The precision feature allows simple sequencing

of multiple power supplies with a resistor divider from another supply. Connecting this pin to ground or to a

voltage less than 1.6 V (typ.) will turn off the regulator. The current drain from the input supply, in this state, is 25

µA (typ.) at an input voltage of 12 V. The EN input has an internal pullup of about 6 µA. Therefore, this pin can

be left floating or pulled to a voltage greater than 2.2 V (typ) to turn the regulator on. The hysteresis on this input

is about 0.6 V (typ.) above the 1.6-V (typ.) threshold. When driving the enable input, the voltage must never

exceed the 6-V absolute maximum specification for this pin.

Although an internal pullup is provided on the EN pin, it is good practice to pull the input high when this feature is

not used, especially in noisy environments. This can most easily be done by connecting a resistor between VIN

and the EN pin. The resistor is required because the internal zener diode at the EN pin will conduct for voltages

above about 6 V. The current in this zener must be limited to less than 100 µA. A resistor of 470 kΩ will limit the

current to a safe value for input voltages as high 42 V. Smaller values of resistor can be used at lower input

voltages.

The LM22678 device also incorporates an input undervoltage lockout (UVLO) feature. This prevents the

regulator from turning on when the input voltage is not great enough to properly bias the internal circuitry. The

rising threshold is 4.3 V (typ.) while the falling threshold is 3.9 V (typ.). In some cases, these thresholds can be

too low to provide good system performance. The solution is to use the EN input as an external UVLO to disable

the part when the input voltage falls below a lower boundary. This is often used to prevent excessive battery

discharge or early turnon during start-up. This method is also recommended to prevent abnormal device

operation in applications where the input voltage falls below the minimum of 4.5 V. Figure 7-1 shows the

connections to implement this method of UVLO. Equation 1 and Equation 2 can be used to determine the correct

resistor values.

(1)

(2)

where

• Voff is the input voltage where the regulator shuts off.

• Von is the voltage where the regulator turns on.

Due to the 6-µA pullup, the current in the divider should be much larger than this. A value of 20 kΩ, for RENB is a

good first choice. Also, a zener diode may be needed between the EN pin and ground, in order to comply with

the absolute maximum ratings on this pin.

Vin

RENB

RENT

Figure 7-1. External UVLO Connections

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7.3.2 Soft Start

The soft-start feature allows the regulator to gradually reach steady-state operation, thus reducing start-up

stresses. The internal soft-start feature brings the output voltage up in about 500 µs. This time is fixed and

cannot be changed. Soft start is reset any time the part is shut down or a thermal overload event occurs.

7.3.3 Bootstrap Supply

The LM22678 device incorporates a floating high-side gate driver to control the power MOSFET. The supply for

this driver is the external bootstrap capacitor connected between the BOOT pin and SW. A good quality 10-nF

ceramic capacitor must be connected to these pins with short, wide PCB traces. One reason the regulator

imposes a minimum off-time is to ensure that this capacitor recharges every switching cycle. A minimum load of

about 5 mA is required to fully recharge the bootstrap capacitor in the minimum off-time. Some of this load can

be provided by the output voltage divider, if used.

7.3.4 Internal Loop Compensation

The LM22678 has internal loop compensation designed to provide a stable regulator over a wide range of

external power stage components.

The internal compensation of the -ADJ option is optimized for output voltages below 5 V. If an output voltage of 5

V or greater is needed, the -5.0 option with an external resistor divider can be used.

Ensuring stability of a design with a specific power stage (inductor and output capacitor) can be tricky. The

LM22678 stability can be verified using the WEBENCH Designer online circuit simulation tool at WEBENCH

Designer. A quick start spreadsheet can also be downloaded from the online product folder.

The complete transfer function for the regulator loop is found by combining the compensation and power stage

transfer functions. The LM22678 has internal type III loop compensation, as detailed in Figure 7-2. This is the

approximate "straight line" function from the FB pin to the input of the PWM modulator. The power stage transfer

function consists of a dc gain and a second order pole created by the inductor and output capacitor or

capacitors. Due to the input voltage feedforward employed in the LM22678, the power stage dc gain is fixed at

20 dB. The second order pole is characterized by its resonant frequency and its quality factor (Q). For a first

pass design, the product of inductance and output capacitance should conform to Equation 3.

(3)

Alternatively, this pole should be placed between 1.5 kHz and 15 kHz and is determined by Equation 4.

(4)

The Q factor depends on the parasitic resistance of the power stage components and is not typically in the

control of the designer. Of course, loop compensation is only one consideration when selecting power stage

components (see Section 8 for more details).

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100 1k 10k 100k 1M 10M

COMPENSATOR GAIN (dB)

FREQUENCY (Hz)

-ADJ

-5.0

Figure 7-2. Compensator Gain

In general, hand calculations or simulations can only aid in selecting good power stage components. Good

design practice dictates that load and line transient testing should be done to verify the stability of the

application. Also, Bode plot measurements should be made to determine stability margins. AN-1889 How to

Measure the Loop Transfer Function of Power Supplies (SNVA364) shows how to perform a loop transfer

function measurement with only an oscilloscope and function generator.

7.4 Device Functional Modes

7.4.1 Shutdown Mode

The EN pin provides electrical ON and OFF control for the LM22678 device. When VEN is below 1.6 V, the

device is in shutdown mode. The current drain from the input supply, in this state, is 25 µA (typ) at an input

voltage of 12 V. The EN input has an internal pullup of about 6 µA. The LM22678 also incorporates an input

undervoltage lockout (UVLO) feature. This prevents the regulator from turning on when the input voltage is not

great enough to properly bias the internal circuitry. The rising threshold is 4.3 V (typ.) while the falling threshold

is 3.9 V (typ.).

7.4.2 Active Mode

The LM22678 device is in active mode when VEN is above the precision enable threshold and its input voltage

is above its UVLO level. The simplest way to enable the LM22678 is to connect the EN pin to VIN through a

resistor. A resistor of 470 kΩ will limit the current to a safe value for input voltages as high 42 V.

7.4.3 Current Limit

The LM22678 device has current limiting to prevent the switch current from exceeding safe values during an

accidental overload on the output. This peak current limit is found in Section 6.6 under the heading of ICL. The

maximum load current that can be provided, before current limit is reached, is determined from Equation 5.

(5)

where

• L is the value of the power inductor.

When the LM22678 device enters current limit, the output voltage will drop and the peak inductor current will be

fixed at ICL at the end of each cycle. The switching frequency will remain constant while the duty cycle drops.

The load current will not remain constant, but will depend on the severity of the overload and the output voltage.

For very severe overloads "short-circuit", the regulator changes to a low frequency current foldback mode of

operation. The frequency foldback is about 1/5 of the nominal switching frequency. This will occur when the

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current limit trips before the minimum on-time has elapsed. This mode of operation is used to prevent inductor

current "run-away", and is associated with very low output voltages when in overload. Equation 6 can be used to

determine what level of output voltage will cause the part to change to low frequency current foldback.

(6)

where

• Fsw is the normal switching frequency.

• Vin is the maximum for the application.

If the overload drives the output voltage to less than or equal to Vx, the part will enter current foldback mode. If a

given application can drive the output voltage to ≤ V x, during an overload, then a second criterion must be

checked. Equation 7 determines the maximum input voltage, when in this mode, before damage occurs.

(7)

where

• Vsc is the value of output voltage during the overload.

• Fsw is the normal switching frequency.

Note

If the input voltage should exceed this value while in foldback mode, the regulator, diode, or both can

be damaged.

It is important to note that the voltages in these equations are measured at the inductor. Normal trace and wiring

resistance will cause the voltage at the inductor to be higher than that at a remote load. Therefore, even if the

load is shorted with zero volts across its terminals, the inductor will still see a finite voltage. It is this value that

should be used for V x and V sc in the calculations. In order to return from foldback mode, the load must be

reduced to a value much lower than that required to initiate foldback. This load "hysteresis" is a normal aspect of

any type of current limit foldback associated with voltage regulators.

The safe operating area, when in short circuit mode, is shown in Figure 7-3. Operating points below and to the

right of the curve represent safe operation.

0.0 0.2 0.4 0.6 0.8 1.0 1.2

INPUT VOLTAGE (v)

SHORT CIRCUIT VOLTAGE (v)

SAFE OPERATING AREA

Figure 7-3. SOA

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7.4.4 Thermal Protection

Internal thermal-shutdown circuitry protects the LM22678 should the maximum junction temperature be

exceeded. This protection is activated at about 150°C, with the result that the regulator will shut down until the

temperature drops below about 135°C.

7.4.5 Duty-Cycle Limits

Ideally, the regulator would control the duty cycle over the full range of zero to one. However due to inherent

delays in the circuitry, there are limits on both the maximum and minimum duty cycles that can be reliably

controlled. This in turn places limits on the maximum and minimum input and output voltages that can be

converted by the LM22678. A minimum on-time is imposed by the regulator to correctly measure the switch

current during a current limit event. A minimum off-time is imposed in order the re-charge the bootstrap

capacitor. Equation 8 can be used to determine the approximate maximum input voltage for a given output

voltage.

(8)

where

• Fsw is the switching frequency.

• TON is the minimum on-time.

Both values can be found in Section 6.6.

The worst case occurs at the lowest output voltage. If the input voltage found in Equation 8 is exceeded, the

regulator will skip cycles; thus, effectively lowering the switching frequency. The consequences of this are higher

output voltage ripple and a degradation of the output voltage accuracy.

The second limitation is the maximum duty cycle before the output voltage will "dropout" of regulation. Equation

9 can be used to approximate the minimum input voltage before dropout occurs.

(9)

where

• The values of TOFF and RDS(ON) are found in Section 6.6.

The worst case here occurs at the highest load. In this equation, RL is the dc inductor resistance. Of course, the

lowest input voltage to the regulator must not be less than 4.5 V (typ.).

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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

The LM22678 device is a step down dc-to-dc regulator. It is typically used to convert a higher dc voltage to a

lower dc voltage with a maximum output current of 5 A. Section 8.2.1.2 can be used to select components for the

LM22678. Alternately, the WEBENCH software may be used to generate complete designs. When generating a

design, the WEBENCH software utilizes iterative design procedure and accesses comprehensive databases of

components. Go to WEBENCH Designer for more details. This section presents a simplified discussion of the

design process.

8.1.1 Output Voltage Divider Selection

For output voltages between about 1.285 V and 5 V, the -ADJ option should be used, with an appropriate voltage

divider as shown in Figure 8-1. Equation 10 can be used to calculate the resistor values of this divider.

(10)

A good value for R FBB is 1 kΩ. This will help to provide some of the minimum load current requirement and

reduce susceptibility to noise pick-up. The top of RFBT should be connected directly to the output capacitor or to

the load for remote sensing. If the divider is connected to the load, a local high-frequency bypass should be

provided at that location.

For output voltages of 5 V, the -5.0 option should be used. In this case no divider is needed and the FB pin is

connected to the output. The approximate values of the internal voltage divider are as follows: 7.38 kΩ from the

FB pin to the input of the error amplifier and 2.55 kΩ from there to ground.

Both the -ADJ and -5.0 options can be used for output voltages greater than 5 V, by using the correct output

divider. As mentioned in Section 7.3.4, the -5.0 option is optimized for output voltages of 5 V. However, for output

voltages greater than 5 V, this option may provide better loop bandwidth than the -ADJ option, in some

applications. If the -5.0 option is to be used at output voltages greater than 5 V, Equation 11 should be used to

determine the resistor values in the output divider.

(11)

Again, a value of RFBB of about 1 kΩ is a good first choice.

Vout

RFBT

RFBB

Figure 8-1. Resistive Feedback Divider

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A maximum value of 10 kΩ is recommended for the sum of R FBB and R FBT to maintain good output voltage

accuracy for the -ADJ option. A maximum of 2 kΩ is recommended for the -5.0 option. For the -5.0 option, the

total internal divider resistance is typically 9.93 kΩ.

In all cases the output voltage divider should be placed as close as possible to the FB pin of the LM22678

device; because this is a high impedance input and is susceptible to noise pick-up.

8.1.2 Power Diode

A Schottky-type power diode is required for all LM22678 applications. Ultra-fast diodes are not recommended

and may result in damage to the IC due to reverse recovery current transients. The near ideal reverse recovery

characteristics and low forward voltage drop of Schottky diodes are particularly important for high input voltage

and low output voltage applications common to the LM22678 device. The reverse breakdown rating of the diode

should be selected for the maximum VIN, plus some safety margin. A good rule of thumb is to select a diode with

a reverse voltage rating of 1.3 times the maximum input voltage.

Select a diode with an average current rating at least equal to the maximum load current that will be seen in the

application.

8.2 Typical Applications

8.2.1 Typical Buck Regulator Application

Figure 8-2 shows an example of converting an input voltage range of 5.5 V to 42 V, to an output of 3.3 V at 5 A.

LM22678-ADJ

GND

VIN

BOOT

GND

VIN 4.5V to 42V

22 PF

6.8 PF

10 nF

4.7 PH

180 PF

GND

RFBT

1.54 k:

RFBB

976:

60V, 5A

VOUT 3.3V

6.8 PF

Figure 8-2. Typical Buck Regulator Application

8.2.1.1 Design Requirements

DESIGN PARAMETERS EXAMPLE VALUE

Driver Supply Voltage (VIN) 4.5 to 42 V

Output Voltage (VOUT) 3.3 V

RFBT Calculated based on RFBB and VREF of 1.285 V.

RFBB 1 kΩ to 10 kΩ

IOUT 5 A

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 External Components

The following guidelines should be used when designing a step-down (buck) converter with the LM22678 device.

8.2.1.2.1.1 Inductor

The inductor value is determined based on the load current, ripple current, and the minimum and maximum input

voltages. To keep the application in continuous conduction mode (CCM), the maximum ripple current, I RIPPLE,

should be less than twice the minimum load current. The general rule of keeping the inductor current peak-to-

peak ripple around 30% of the nominal output current is a good compromise between excessive output voltage

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ripple and excessive component size and cost. Using this value of ripple current, the value of inductor (L) is

calculated using Equation 12.

(12)

where

• Fsw is the switching frequency.

• Vin should be taken at its maximum value, for the given application.

Equation 12 provides a guide to select the value of the inductor L; the nearest standard value will then be used

in the circuit.

Once the inductor is selected, the actual ripple current can be determined by Equation 13.

(13)

Increasing the inductance will generally slow down the transient response but reduce the output voltage ripple.

Reducing the inductance will generally improve the transient response but increase the output voltage ripple.

The inductor must be rated for the peak current, IPK, in a given application, to prevent saturation. During normal

loading conditions, the peak current is equal to the load current plus 1/2 of the inductor ripple current.

During an overload condition, as well as during certain load transients, the controller can trip current limit. In this

case the peak inductor current is given by I CL, found in Section 6.6. Good design practice requires that the

inductor rating be adequate for this overload condition.

Note

If the inductor is not rated for the maximum expected current, it can saturate resulting in damage to

the LM22678, the power diode, or both.

8.2.1.2.2 Input Capacitor

The input capacitor selection is based on both input voltage ripple and RMS current. Good quality input

capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the regulator current

during switch on-time. Low-ESR ceramic capacitors are preferred. Larger values of input capacitance are

desirable to reduce voltage ripple and noise on the input supply. This noise can find its way into other circuitry,

sharing the same input supply, unless adequate bypassing is provided. A very approximate formula for

determining the input voltage ripple is shown in Equation 14.

(14)

where

• Vri is the peak-to-peak ripple voltage at the switching frequency.

Another concern is the RMS current passing through this capacitor. Equation 15 determines an approximation to

this current.

(15)

The capacitor must be rated for at least this level of RMS current at the switching frequency.

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All ceramic capacitors have large voltage coefficients, in addition to normal tolerances and temperature

coefficients. To help mitigate these effects, multiple capacitors can be used in parallel to bring the minimum

capacitance up to the desired value. This can also help with RMS current constraints by sharing the current

among several capacitors. Many times it is desirable to use an electrolytic capacitor on the input, in parallel with

the ceramics. The moderate ESR of this capacitor can help to damp any ringing on the input supply caused by

long power leads. This method can also help to reduce voltage spikes that may exceed the maximum input

voltage rating of the LM22678 device.

It is good practice to include a high frequency bypass capacitor as close as possible to the LM22678 device.

This small case size, low ESR ceramic capacitor should be connected directly to the VIN and GND pins with the

shortest possible PCB traces. Values in the range of 0.47 µF to 1 µF are appropriate. This capacitor helps to

provide a low impedance supply to sensitive internal circuitry. It also helps to suppress any fast noise spikes on

the input supply that may lead to increased EMI.

8.2.1.2.3 Output Capacitor

The output capacitor is responsible for filtering the output voltage and supplying load current during transients.

Capacitor selection depends on application conditions as well as ripple and transient requirements. Best

performance is achieved with a parallel combination of ceramic capacitors and a low-ESR SP™ or POSCAP™

type. Very low ESR capacitors such as ceramics reduce the output ripple and noise spikes, while higher value

electrolytics or polymer provide large bulk capacitance to supply transients. Assuming very low ESR, Equation

16 determines an approximation to the output voltage ripple.

(16)

Typically, a total value of 100 µF or greater is recommended for output capacitance.

In applications with Vout less than 3.3 V, it is critical that low-ESR output capacitors are selected. This will limit

potential output voltage overshoots as the input voltage falls below the device normal operating range.

8.2.1.2.4 Bootstrap Capacitor

The bootstrap capacitor between the BOOT pin and the SW pin supplies the gate current to turn on the N-

channel MOSFET. The recommended value of this capacitor is 10 nF and should be a good quality, low-ESR

ceramic capacitor. In some cases, it can be desirable to slow down the turnon of the internal power MOSFET in

order to reduce EMI. This can be done by placing a small resistor in series with the Cboot capacitor. Resistors in

the range of 10 Ω to 50 Ω can be used. This technique should only be used when absolutely necessary, because

it will increase switching losses and thereby reduce efficiency.

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8.2.1.3 Application Curves

Figure 8-3. Efficiency vs IOUT and VIN, VOUT = 3.3 V Figure 8-4. Normalized Feedback Voltage vs Input

Voltage

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Power Supply Recommendations

The LM22678 device is designed to operate from an input voltage supply range between 4.5 V and 42 V. This

input supply should be well regulated and able to withstand maximum input current and maintain a stable

voltage. The resistance of the input supply rail should be low enough that an input current transient does not

cause a high enough drop at the LM22678 supply voltage that can cause a false UVLO fault triggering and

system reset. If the input supply is located more than a few inches from the LM22678 device, additional bulk

capacitance may be required in addition to the ceramic bypass capacitors. The amount of bulk capacitance is

not critical, but a 47 µF or 100 µF electrolytic capacitor is a typical choice.

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9 Layout

9.1 Layout Guidelines

Board layout is critical for the proper operation of switching power supplies. First, the ground plane area must be

sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce the effects

of switching noise. Switch mode converters are very fast switching devices. In such cases, the rapid increase of

input current combined with the parasitic trace inductance generates unwanted L di/dt noise spikes. The

magnitude of this noise tends to increase as the output current increases. This noise may turn into

electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, care must

be taken in layout to minimize the effect of this switching noise.

The most important layout rule is to keep the ac current loops as small as possible. Figure 9-1 shows the current

flow in a buck converter. The top schematic shows a dotted line which represents the current flow during the FET

switch on-state. The middle schematic shows the current flow during the FET switch off-state.

The bottom schematic shows the currents referred to as ac currents. These ac currents are the most critical

because they are changing in a very short time period. The dotted lines of the bottom schematic are the traces to

keep as short and wide as possible. This will also yield a small loop area reducing the loop inductance. To avoid

functional problems due to layout, review the PCB layout example. Best results are achieved if the placement of

the LM22678 device, the bypass capacitor, the Schottky diode, R FBB, R FBT, and the inductor are placed as

shown in Figure 9-1. In the layout shown, R1 = RFBB and R2 = RFBT. It is also recommended to use 2 oz copper

boards or heavier to help thermal dissipation and to reduce the parasitic inductances of board traces. See

AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for more information.

Figure 9-1. Current Flow in a Buck Application

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9.2 Layout Example

Figure 9-2. LM22678 Layout Example

9.3 Thermal Considerations

The components with the highest power dissipation are the power diode and the power MOSFET internal to the

LM22678 regulator. The easiest method to determine the power dissipation within the LM22678 is to measure

the total conversion losses then subtract the power losses in the diode and inductor. The total conversion loss is

the difference between the input power and the output power. An approximation for the power diode loss is

shown in Equation 17.

(17)

where

• VD is the diode voltage drop.

An approximation for the inductor power is determined by Equation 18.

(18)

where

• RL is the dc resistance of the inductor.

The 1.1 factor is an approximation for the ac losses.

The regulator has an exposed thermal pad to aid power dissipation. Adding multiple vias under the device to the

ground plane will greatly reduce the regulator junction temperature. Selecting a diode with an exposed pad will

also aid the power dissipation of the diode. The most significant variables that affect the power dissipation of the

regulator are output current, input voltage and operating frequency. The power dissipated while operating near

the maximum output current and maximum input voltage can be appreciable. The junction-to-ambient thermal

resistance of the LM22678 will vary with the application. The most significant variables are the area of copper in

the PC board, the number of vias under the IC exposed pad and the amount of forced air cooling provided. A

large continuous ground plane on the top or bottom PCB layer will provide the most effective heat dissipation.

The integrity of the solder connection from the IC exposed pad to the PC board is critical. Excessive voids will

greatly diminish the thermal dissipation capacity. The junction-to-ambient thermal resistance of the LM22678

PFM package is specified in Section 6.6. See AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419) for

more information.

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10 Device and Documentation Support

10.1 Documentation Support

10.1.1 Related Documentation

•AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419)

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

•AN-1892 LM22677 Evaluation Board (SNVA366)

•AN-1889 How to Measure the Loop Transfer Function of Power Supplies (SNVA364)

10.2 Support Resources

TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight

from the experts. Search existing answers or ask your own question to get the quick design help you need.

Linked content is 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.

10.3 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. Click on

Subscribe to updates to register and receive a weekly digest of any product information that has changed. For

change details, review the revision history included in any revised document.

10.4 Electrostatic Discharge Caution

This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled

with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.

ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may

be more susceptible to damage because very small parametric changes could cause the device not to meet its published

specifications.

10.5 Glossary

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

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.

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Product Folder Links: LM22678 LM22678-Q1

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM22678QTJ-5.0/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

QTJ-5.0

LM22678QTJ-ADJ/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

QTJ-ADJ

LM22678QTJE-5.0/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

QTJ-5.0

LM22678QTJE-ADJ/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

QTJ-ADJ

LM22678TJ-5.0/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

TJ-5.0

LM22678TJ-ADJ/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

TJ-ADJ

LM22678TJE-5.0/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

TJ-5.0

LM22678TJE-ADJ/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22678

TJ-ADJ

(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.

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 2

(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 finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material 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 LM22678, LM22678-Q1 :

•Catalog: LM22678

•Automotive: LM22678-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

LM22678QTJ-5.0/NOPB TO-263 NDR 7 1000 330.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678QTJ-ADJ/NOPB TO-263 NDR 7 1000 330.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678QTJE-5.0/NOPB TO-263 NDR 7 250 178.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678QTJE-ADJ/NOP

BTO-263 NDR 7 250 178.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678TJ-5.0/NOPB TO-263 NDR 7 1000 330.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678TJ-ADJ/NOPB TO-263 NDR 7 1000 330.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678TJE-5.0/NOPB TO-263 NDR 7 250 178.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

LM22678TJE-ADJ/NOPB TO-263 NDR 7 250 178.0 24.4 10.6 15.4 2.45 12.0 24.0 Q2

PACKAGE MATERIALS INFORMATION

www.ti.com 2-Oct-2020

Pack Materials-Page 1

*All dimensions are nominal

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

LM22678QTJ-5.0/NOPB TO-263 NDR 7 1000 367.0 367.0 35.0

LM22678QTJ-ADJ/NOPB TO-263 NDR 7 1000 367.0 367.0 35.0

LM22678QTJE-5.0/NOPB TO-263 NDR 7 250 210.0 185.0 35.0

LM22678QTJE-ADJ/NOPB TO-263 NDR 7 250 210.0 185.0 35.0

LM22678TJ-5.0/NOPB TO-263 NDR 7 1000 367.0 367.0 35.0

LM22678TJ-ADJ/NOPB TO-263 NDR 7 1000 367.0 367.0 35.0

LM22678TJE-5.0/NOPB TO-263 NDR 7 250 210.0 185.0 35.0

LM22678TJE-ADJ/NOPB TO-263 NDR 7 250 210.0 185.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 2-Oct-2020

Pack Materials-Page 2

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PACKAGE OUTLINE

-60

10.1

9.6

10.41

9.91

2.1

1.9

1.05

0.95

10.76

10.26

12.45

11.95

14.36

13.66

0-0.15

STAND-OFF

NOTE 5

R0.7

MAX TYP

ALL AROUND

(2.66) 6.5

6.1

5.75

5.40

7.1

6.5

6.6

6.3

4.1

3.9

1.05

0.65

6.11

5.85

7X 0.735

0.635

6X 1.27

7.62

7X 0.508

0.381

4219872/A 04/2019

TO-263 - 2.25 mm max heightNDR0007A

TO-263

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. Features may not exist and shape may vary per different assembly sites.

4. Reference JEDEC registration TO-279B.

5. Under all conditions, leads must not be above Datum C

SCALE 1.000

0.15

0.25 C A B 1

PIN 1 ID

EXPOSED PAD

(OUTLINE DOES NOT

INCLUDE MOLD FLASH)

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EXAMPLE BOARD LAYOUT

0.07 MAX

ALL AROUND 0.07 MIN

ALL AROUND

(6.35)

(5.59)

(0.91)(8.28)

6X (1.27)

(7.62)

7X (2.41)

7X (0.91)

4219872/A 04/2019

TO-263 - 2.25 mm max heightNDR0007A

TO-263

NOTES: (continued)

6. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature numbers

SLMA002(www.ti.com/lit/slm002) and SLMA004 (www.ti.com/lit/slma004).

7. Vias are optional depending on application, refer to device data sheet. It is recommended that vias under paste be filled, plugged or tented.

OPENING

SOLDER MASK METAL

NON SOLDER MASK

DEFINED

SOLDER MASK DETAILS

EXPOSED

METAL

SOLDER MASK

OPENING

SOLDER MASK

METAL UNDER

SOLDER MASK

DEFINED

EXPOSED

METAL

SYMM

PKG

www.ti.com

EXAMPLE STENCIL DESIGN

20X (1)

20X (1.13)

R(0.05) TYP

(1.2) TYP

(1.33) TYP

(0.665)

(0.29)

0.91(8.28)

(7.62)

6X (1.27)

7X (2.41) 7X (0.91)

4219872/A 04/2019

TO-263 - 2.25 mm max heightNDR0007A

TO-263

NOTES: (continued)

8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

9. Board assembly site may have different recommendations for stencil design.

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

EXPOSED PAD

64% PRINTED SOLDER COVERAGE BY AREA

SCALE:7X

8SYMM

PKG

EXPOSED METAL

TYP

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