Texas Instruments LMR38020EVM Manuale utente

User’s Guide

LMR38020EVM User Guide

ABSTRACT

The LMR38020EVM is a 80 V DC/DC buck regulator that employs synchronous rectification to achieve high

conversion efficiency in a small footprint. The EVM operates over a wide input voltage range of 6 V to 80 V

to provide a regulated 5 V output at 400 kHz switching frequency. The output voltage has better than 1.5%

setpoint accuracy and is adjustable using an external resistor divider. The module design uses the LMR38020F

synchronous buck converter with wide input voltage (wide VIN) range, wide duty-cycle range, integrated high-

side and low-side power MOSFETs, cycle-by-cycle overcurrent protection, and precision enable. The LMR38020

converter is available in an 8-pin SO PowerPAD™ package to enable high density, low component count DC/DC

solutions. The LMR38020EVM evaluation module is qualified for the LMR38020 as well as the LMR38020-Q1

buck converter. See Table 1-1 for package information.

Table 1-1. Device and Package Configurations

CONVERTER IC PACKAGE

U1 LMR38020-Q1 8-pin SO package with PowerPAD (4.89 mm × 3.90 mm)

LMR38020

Table of Contents

1 General TI High Voltage Evaluation User Safety Guidelines.............................................................................................. 2

2 LMR38020 Evaluation Module............................................................................................................................................... 4

2.1 Quick Start Procedure........................................................................................................................................................4

2.2 Detailed Descriptions......................................................................................................................................................... 5

3 Schematic................................................................................................................................................................................7

4 PCB Layout..............................................................................................................................................................................8

5 Bill of Materials......................................................................................................................................................................11

List of Figures

Figure 2-1. LMR38020EVM Top View..........................................................................................................................................4

Figure 3-1. LMR38020EVM Schematic....................................................................................................................................... 7

Figure 4-1. Top Layer and Silkscreen Layer................................................................................................................................ 8

Figure 4-2. Mid-Layer 1 Ground Plane........................................................................................................................................ 9

Figure 4-3. Mid-Layer 2 Routing.................................................................................................................................................. 9

Figure 4-4. Bottom Layer Routing..............................................................................................................................................10

List of Tables

Table 1-1. Device and Package Configurations...........................................................................................................................1

Table 5-1. LMR38020EVM Bill of Materials................................................................................................................................11

Trademarks

PowerPAD™ is a trademark of Texas Instruments.

All trademarks are the property of their respective owners.

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LMR38020EVM User Guide 1

1 General TI High Voltage Evaluation User Safety Guidelines

WARNING

Always follow TI’s set-up and application instructions, including use of all interface components within their

recommended electrical rated voltage and power limits. Always use electrical safety precautions to help ensure

your personal safety and the safety of those working around you. Contact TI’s Product Information Center http://

support.ti.com for further information.

Save all warnings and instructions for future reference.

Failure to follow warnings and instructions may result in personal injury, property damage, or death due

to electrical shock and/or burn hazards.

The term TI HV EVM refers to an electronic device typically provided as an open framed, unenclosed printed-

circuit board assembly. It is intended strictly for use in development laboratory environments, solely for qualified

professional users having training, expertise, and knowledge of electrical safety risks in development and

application of high-voltage electrical circuits. Any other use and/or application are strictly prohibited by Texas

Instruments. If you are not suitably qualified, you should immediately stop from further use of the HV EVM.

•Work Area Safety:

– Maintain a clean and orderly work area.

– Qualified observer(s) must be present anytime circuits are energized.

– Effective barriers and signage must be present in the area where the TI HV EVM and its interface

electronics are energized, indicating operation of accessible high voltages may be present, for the

purpose of protecting inadvertent access.

– All interface circuits, power supplies, evaluation modules, instruments, meters, scopes, and other related

apparatus used in a development environment exceeding 50 VRMS/75 VDC must be electrically located

within a protected Emergency Power Off (EPO) protected power strip.

– Use a stable and non-conductive work surface.

– Use adequately insulated clamps and wires to attach measurement probes and instruments. No freehand

testing whenever possible.

•Electrical Safety:

As a precautionary measure, it is always a good engineering practice to assume that the entire EVM may

have fully accessible and active high voltages.

– De-energize the TI HV EVM and all its inputs, outputs, and electrical loads before performing any

electrical or other diagnostic measurements. Confirm that TI HV EVM power has been safely de-

energized.

– With the EVM confirmed de-energized, proceed with required electrical circuit configurations, wiring,

measurement equipment hook-ups, and other application needs, while still assuming the EVM circuit and

measuring instruments are electrically live.

– When EVM readiness is complete, energize the EVM as intended.

WARNING

WARNING: While the EVM is energized, never touch the EVM or its electrical circuits as

they could be at high voltages capable of causing electrical shock hazard.

General TI High Voltage Evaluation User Safety Guidelines www.ti.com

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•Personal Safety:

– Wear personal protective equipment, for example, latex gloves and/or safety glasses with side shields or

protect EVM in an adequate lucent plastic box with interlocks from accidental touch.

•Limitation for Safe Use:

– EVMs are not to be used as all or part of a production unit.

Safety and Precautions

The EVM is designed for professionals who have received the appropriate technical training, and is designed

to operate from an AC power supply or a high-voltage DC supply. Please read this user guide and the safety-

related documents that come with the EVM package before operating this EVM.

CAUTION

Do not leave the EVM powered when unattended.

WARNING

Hot surface! Contact may cause burns. Do not touch!

WARNING

High Voltage! Electric shock is possible when connecting board to live wire. Board should be

handled with care by a professional.

For safety, use of isolated test equipment with overvoltage and overcurrent protection is highly

recommended.

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LMR38020EVM User Guide 3

2 LMR38020 Evaluation Module

The LMR38020EVM is configured to deliver 5 V and 2 A at a switching frequency of 400 kHz.

• Tightly-regulated output voltage of 5 V with 1.5% setpoint accuracy

• Wide input voltage operating range of 4.5 V to 80 V

• 98% maximum duty cycle

• Force PWM operation to achieve low output voltage ripple, tight output voltage regulation at light load

• Frequency synchronization to external clock

• PWRGD signal indicates output regulation

• Support startup with pre-biased output

• Programmable system UVLO via precision enable

• Fully assembled, tested and proven PCB layout

2.1 Quick Start Procedure

1. Connect the voltage supply between VIN and GND connectors using short wires.

2. Connect the load of the converter between VOUT and GND connectors using short wires.

3. Set the supply voltage (VIN) at an appropriate level between 6 V to 80 V. Set the current limit of the supply to

an appropriate level as well.

4. Turn on the power supply. The EVM powers up and provides VOUT = 5 V.

5. Monitor the output voltage while increasing the load current to 2 A max.

See Figure 2-1 for the location of the connectors.

Figure 2-1. LMR38020EVM Top View

CAUTION

Caution Hot surface.

Contact may cause burns.

Do not touch.

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2.2 Detailed Descriptions

This section describes the connectors and the test points on the EVM and how to properly connect, set up and

use the LMR38020EVM. See Figure 2-1 for a top view of the EVM.

VOUT (J2) Output voltage of the converter

VOUT connector and test point connected to the power inductor and the output capacitors.

Connect the loading device between VOUT and GND connectors to provide loading to the

regulator. Connect the loading device to the board with short wires to handle the DC output current.

GND Ground of the converter

It is connected to the LMR38020 GND as well as the return terminals of the input and output

capacitors. GND is the current return path for both supply voltage and load. Connect to supply and

load grounds with short wires.

VIN (J3) Input voltage to the converter

VIN connector and test point connects to the input capacitors and the VIN pin of the LMR38020.

Connect the supply voltage from a power supply or a battery between the VIN and GND

connectors. The voltage range should be higher than 4.5 V for the device to be active. VVIN higher

than 6 V provides a regulated 5 V output voltage. To avoid damaging the device VVIN should be

no greater than 80 V. The current limit on the supply should be high enough to provide the needed

supply current when the output is fully loaded. The supply voltage should be connected to the

board with short wires.

EMI IN+ Input voltage to input filter of the converter

If an input filter is desired between the supply voltage and the LMR38020, connect the supply

voltage between EMI IN+ and EMI GND on bottom layer. The supply voltage should be connected

to the board with short wires.

The EMI filter components were not assembled on this evaluation board.

EMI GND Ground connection near the input filter

This is the current return path for the supply connected to EMI IN+. It provides a direct connection

to the input filter capacitors to filter conducted noise generated by the converter. Use EMI IN+ and

EMI GND connections at the input filter to minimize EMI.

SYNC (J5) SYNC clock injection

J5 is used to synchronize the switching frequency to external clock. Refer to data sheet for detail

application information.

Do NOT short J5 SYNC pin to ground.

EN (J4) Set EN pin options

Use this jumper to enable/disable the LMR38020. PIN-1 is connected to GND and PIN-2 is

connected to EN.

1. Connect PIN-1 to PIN-2 to disable the device.

2. Leave PIN-1 and PIN-2 open for EN to be connected to VIN through a resistor divider.

The system UVLO voltage can be programmed by resistor divider on EN pin. The lower UVLO

resistor, R7, was not assembled on this board, so the EN/UVLO voltage pulls up to the input

voltage.

Calculate the lower UVLO resistor, R7, based on the desired turn-on voltage and the upper UVLO

resistor, R5, of 115 KΩ. Refer to LMR38020 data sheet "External UVLO" section for more detail

application information.

PWRGD

(J1)

Power Good indication

PWRGD jumper with PIN-1 connected to PGOOD and PIN-2 connected to Pull-Up voltage. PIN-1

can be used as a test point to monitor the power-good indicator. This flag indicates whether the

output voltage has reached its regulation level. The LMR38020 PGOOD is an open-drain output

that is tied to voltage below 20 V through pull-up resistor R10.

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LMR38020EVM User Guide 5

Header

(J6)

Measure Vout and loop response

J6 PIN-2 is connected to output for output voltage sensing and efficiency measurement. PIN-1 is

connected to the noise injection resistor R3. The loop response can be measured on J6.

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3 Schematic

Figure 3-1. LMR38020EVM Schematic

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LMR38020EVM User Guide 7

4 PCB Layout

Figure 4-1 through Figure 4-4 show the board layout for the LMR38020EVM. The EVM offers resistors,

capacitors, and test points to configure the output voltage, precision enable, and switching frequency.

The 8-pin SO PowerPAD™ package offers an exposed thermal pad, which must be soldered to the copper

landing on the PCB for optimal thermal performance. The PCB consists of a 4-layer design. There are 2-oz

copper planes on the top and bottom and 1-oz copper mid-layer planes to dissipate heat with an array of thermal

vias under the thermal pad to connect to all four layers.

Test points have been provided for ease of use to connect the power supply, required load, and to monitor critical

signals.

Figure 4-1. Top Layer and Silkscreen Layer

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Figure 4-2. Mid-Layer 1 Ground Plane

Figure 4-3. Mid-Layer 2 Routing

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LMR38020EVM User Guide 9

Figure 4-4. Bottom Layer Routing

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