Powering and Loading Considerations
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3
Powering and Loading Considerations
Read this entire section prior to attempting to power the evaluation board.
3.1
Quick Start Procedure
Step 1: Set the bench power supply current limit to 3A. Set the power supply voltage to 4V. Turn off the
power supply output. Connect the power supply to the LMR10530 demo board. Positive connection to V
IN
and negative connection to GND.
Step 2: Connect a load, as high as 3A, to the V
OUT
terminal. Positive connection to V
OUT
and negative
connection to GND.
Step 3: The EN pin should be left open for normal operation.
Step 4: Turn on the bench power supply with no load applied to the LMR10530. The V
OUT
would be in
regulation at a nominal 1.2V output.
Step 5: Slowly increase the load while monitoring the output voltage, V
OUT
should remain in regulation as
the load is increased up to 3 Amps. The LMR10530 is designed to skip some pulses at very light loads to
maintain output voltage regulation. Depending on load levels, the circuit may operate in either
discontinuous or continuous conduction mode.
Step 6: Slowly sweep the input voltage from 3 to 5.5V, V
OUT
should remain in regulation with a nominal
1.2V output.
3.2
Starting Up
By default, VINC is connected to V
IN
through a low pass filter to remove any high frequency noise present
at the input. EN is connected to VINC through a 100k
Ω
resistor. A separate logic signal at the EN terminal
can be used, if startup and shutdown need to be controlled. The EN pin is tied to V
IN
to simplify start-up.
The pull-up resistor allows the power supply design engineer to toggle EN independently, if desired, and
observe the start-up behavior of the LMR10530.
3.3
Adjusting the Output Voltage
The output voltage is set using the following equation where R
fbb
is connected between the FB pin and
GND, and R
fbt
is connected between V
OUT
and FB.
V
OUT
= V
FB
(1 + (R
fbt
/R
fbb
))
(1)
The feedback voltage VFB is regulated at 0.60V typically.
Adjusting the output voltage will affect the performance of the LMR10530. In addition, output capacitors
might not be rated for the new output voltage. For more information, see LMR10530 SIMPLE SWITCHER
5.5Vin, 3.0A Step-Down Voltage Regulator in WSON-10 (
SNVS814
).
2
AN-2280 LMR10530 Evaluation Module
SNVU192A – October 2012 – Revised April 2013
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