National Semiconductor
Application Note 2066
Eric Lee
LM25119 Evaluation Board
September 28, 2010
ed to the J6 (OUT2+) and J5 (OUT2-/GND). Be sure to
choose the correct connector and wire size when attaching
the source power supply and the load.
Introduction
The LM25119EVAL evaluation board provides the design en-
gineer with a fully functional dual output buck converter, em-
ploying the LM25119 Dual Emulated Current Mode Syn-
chronous Buck Controller. The evaluation board is designed
to provide both 3.3V and 1.8V outputs over an input range of
6.0V to 36V. Also the evaluation board can be easily config-
ured for a single 3.3V, 16A regulator.
SOURCE POWER
The power supply and cabling must present low impedance
to the evaluation board. Insufficient cabling or a high
impedance power supply will droop during power supply ap-
plication with the evaluation board inrush current. If large
enough, this droop will cause a chattering condition during
power up. During power down, insufficient cabling or a high
impedance power supply will overshoot. This overshoot will
cause a non-monotonic decay on the output.
Performance of the Evaluation
Board
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Input Voltage Range: 6.0V to 36V
Output Voltage: 3.3V (CH1), 1.8V (CH2)
Output Current: 8A (CH1), 8A (CH2)
Nominal Switching Frequency: 230 KHz
Synchronous Buck Operation: Yes
Diode Emulation Mode: Yes
An additional external bulk input capacitor may be required
unless the output voltage droop/overshoot of the source pow-
er is less than 0.5V. In this board design, UVLO setting is
conservative while UVLO hysteresis setting is aggressive.
Minimum input voltage can goes down with an aggressive
design. Minimum operating input voltage depends on the out-
put voltage droop/overshoot of the source power supply and
the forced off-time of the LM25119. Refer to the LM25119
datasheet for complete design information.
Hiccup Mode Overload Protection: Yes
External VCC Sourcing: No
LOADING
Powering and Loading
Consideration
When applying power to the LM25119 evaluation board, cer-
tain precautions need to be followed. A misconnection can
damage the assembly.
When using an electronic load, it is strongly recommended to
power up the evaluation board at light load and then slowly
increase the load. If it is desired to power up the evaluation
board at maximum load, resistor banks must be used. In gen-
eral, electronic loads are best suited for monitoring steady
state waveforms.
PROPER BOARD CONNECTION
AIR FLOW
The input connections are made to the J1 (VIN) and J2 (RTN/
GND) connectors. The CH1 load is connected to the J3
(OUT1+) and J4 (OUT1-/GND) and the CH2 load is connect-
Prolonged operation with high input voltage at full power will
cause the MOSFETs to overheat. A fan with a minimum of
200LFM should be always provided.
30126101
FIGURE 1. Typical Evaluation Setup
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