Texas Instruments LM25088 User Manual
1 Introduction
The LM25088 evaluation board is designed to provide the design engineer with a fully functional power
converter based on emulated current mode control to evaluate the LM25088 controller IC. The LM25088
evaluation board is available in two versions (like the LM25088 controller): the LM25088-1 evaluation
board provides ±5% oscillator frequency dithering to reduce EMI and the LM25088-2 evaluation board
provides hiccup mode restart to reduce over load stress. Both the evaluation boards share the same
layout except for silkscreen. The printed circuit board consists of two layers, 2 ounce of copper top and
bottom and the board size is 2.55x1.5x0.5 inches.
Specification LM25088-1 LM25088-2
Input Voltage Range 5.5V to 36V 5.5V to 36V
Output Voltage 5.0V 5.0V
Max. Average Load Current 7A 7A
Load Regulation 2% 2%
Current Limit Type Cycle-by-cycle current limit Hiccup Mode Restart
Frequency 250 kHz (±5% Oscillator Dithering) 250 kHz
User's Guide
SNVA383D–November 2008–Revised April 2013
AN-1931 LM25088 Evaluation Board
Figure 1. Typical Efficiency Curves of LM25088-1 and LM25088-2 Evaluation Boards
2 Powering and Loading Considerations
Read this entire page prior to attempting to power the evaluation board.
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Powering and Loading Considerations
2.1 Quick Setup Procedure
1. Set the power supply current limit to 10A. Turn off the power supply. Connect the power supply to the
VIN terminals.
2. Connect the load, with a 7A capability, to the VOUT terminals.
3. Slowly increase the load while monitoring the output, VOUT should be in regulation with a nominal 5V
output.
4. Slowly sweep the input voltage from 5.5V to 36V, VOUT should remain in regulation with a nominal 5V
output
5. Temporarily short the EN pin to check the shutdown function, Also, EN pin can be set between 0.4V
and 1.2V, for example, by shorting EN pin to ground with a diode, to check the standby function.
6. Increase the load beyond the rated current to check the current limiting. The output current should limit
at approximately 10A. The LM25088-1 board will enter cycle-by-cycle current limiting, while LM25088-2
is configured for a hiccup mode restart. Cooling is critical in this step.
2.2 Air Flow
Prolonged operation with high input voltage (>24V) at full load will cause the LM25088 and MOSFETs to
overheat and could potentially result in thermal shutdown. A fan with a minimum of 100LFM should always
be used to cool the LM25088 evaluation board.
2.3 Powering Up
It is suggested that the load be kept low during the first power up. Set the current limit of the source
supply to provide about 1.5 times the anticipated wattage of the load. A quick efficiency check is the best
way to confirm that everything is operating properly. If something is amiss one can be reasonably sure
that it will affect the efficiency adversely. Few parameters can be correct in a switching power supply
without creating losses and potentially damaging heat.
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2.4 Over Current Protection
The LM25088-1 and LM25088-2 evaluation boards are both configured with over-current protection
schemes. The LM25088-1 employs a cycle-by-cycle current limiting, while the LM25088-2 is configured for
a hiccup mode restart. Please refer the LM25088/LM25088Q Wide Input Range Non-Synchronous Buck
Controller (SNVS609) data sheet for more information on RES pin.
2.5 Synchronization
A Sync pin has been provided on the evaluation board. This pin can be used to synchronize the LM25088
to an external clock. It is recommended not to exceed 500 kHz while synchronizing. Refer the LM25088
datasheet for complete information.
2.6 Active Loads
When using electronic load, it is strongly recommended to power up the evaluation board at light load and
then slowly increase the load. This is necessary as most of the electronic loads do not draw any current till
the output reaches an internally set point; this can result in soft-start function to not work as desired and
can trip the current sense comparator. Electronic loads, in general, are best suited for monitoring steady
state waveforms. If it is desired to power up the evaluation board at maximum load, resistor banks can be
used. This will ensure a soft-start and evaluation board will perform as desired. Ensure that there is
sufficient cooling for both the resistor banks and the LM25088 evaluation board, while running at full load.
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AN-1931 LM25088 Evaluation Board SNVA383D–November 2008–Revised April 2013
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Typical Performance Waveforms of LM25088-1 and LM25088-2 Evaluation Boards
Figure 2. Typical Thermal Profile at 48VIN
3 Typical Performance Waveforms of LM25088-1 and LM25088-2 Evaluation Boards
Conditions:
Input Voltage = 24VDC
Output Current = 4A to 7A
Bandwidth Limit = 20 MHz
Traces:
Bottom Trace: Output Current
Amps/div = 2A
Top Trace: Output Voltage response
Volts/div = 100 mV
Horizontal Resolution = 500 µs/div
Figure 3. Transient Response
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