Texas Instruments LM38020EVM User manual

User’s Guide
LMR38020EVM User Guide
ABSTRACT
The LM38020EVM is an 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 the following:
• Wide input voltage (wide VIN) range
• Wide duty-cycle range
• Integrated high-side and low-side power MOSFETs
• Cycle-by-cycle overcurrent protection
• Precision enable
The LMR38020 converter is available in an 8-pin SO PowerPAD™ integrated circuit 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
6 Revision History....................................................................................................................................................................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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1 General TI High Voltage Evaluation User Safety Guidelines
WARNING
Always follow TI’s setup 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
the user's personal safety and the safety of those working around the user. Contact TI’s Product Information
Center TI's Product Information Center for further information.
Save all warnings and instructions for future reference.
Failure to follow warnings and instructions can result in personal injury, property damage, or death due
to electrical shock, burn hazards, or both.
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 that have training, expertise, and knowledge of electrical safety risks in development and
application of high-voltage electrical circuits. Any other use, application, or both, are strictly prohibited by Texas
Instruments. If the user is not suitably qualified, the user should immediately stop from further use of the HV
EVM.
•Work Area Safety:
– Maintain a clean and orderly work area.
– Qualified observer or observers must be present any time 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 can 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.
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•Personal Safety:
– Wear personal protective equipment, for example, latex gloves, safety glasses with side shields, or both,
or protect the 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's 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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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 4.2 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
• Supports start-up with pre-biased output
• Programmable system UVLO through 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 maximum.
See Figure 2-1 for the location of the connectors.
Figure 2-1. LMR38020EVM Top View
WARNING
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
GND 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 must be higher than 4.2 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 must be
no greater than 80 V. The current limit on the supply must be high enough to provide the needed
supply current when the output is fully loaded. The supply voltage must be connected to the
board with short wires.
VIN_EMI 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 VIN_EMI and GND on the bottom layer. The supply voltage must be connected
to the board with short wires.
The EMI filter components were not assembled on this evaluation board.
VIN_S(TP1) Measure VIN voltage
It provides a direct connection to the input capacitor C10 to sense the input voltage. Do not apply
input voltage on this test pin.
SYNC (J5) SYNC clock injection
J5 is used to synchronize the switching frequency to external clock. Refer to the LMR38020
SIMPLE SWITCHER® 4.2-V to 80-V, 2-A Synchronous Buck Converter 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 the External UVLO section of the LMR38020 SIMPLE
SWITCHER® 4.2-V to 80-V, 2-A Synchronous Buck Converter Data Sheet for more detailed
application information.
PWRGD (J1) Power-good indication
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PWRGD jumper with PIN-1 connected to PGOOD and PIN-2 connected to the pullup 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 pullup resistor R10.
Header (J6) Measure VOUT and loop response
J6 PIN-2 (VO_S) is connected to the output for output voltage sensing and efficiency
measurement. PIN-1 (Vinj) 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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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 integrated circuit 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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Figure 4-4. Bottom Layer Routing
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