User's Guide
SNVA353B – February 2009 – Revised April 2013
AN-1870 LM26420 Evaluation Board
1
Introduction
The LM26420 evaluation board was designed to provide two 2A outputs, V
OUT1
and V
OUT2
. It is available in
either the HTSSOP package option of the LM26420 for easier probing or the WQFN version for evaluating
the smaller package. The design emphasizes on the compactness of the LM26420 PCB layout and is
thermally optimized. The total solution size is less than 35mm by 40mm. The board supports the
conversion from an input voltage ranging from 3V to 5.5V down to output voltages of 0.8V for each
channel. V
OUT1
and V
OUT2
are set to 1.2V and 2.5V respectively. The feedback resistor can be changed to
support output voltages as low as 0.8V or as high at 4.5V, assuming V
IN
is high enough to support it. The
EN pins are pulled up to V
IN
by jumpers for easy evaluation but can also be easily controlled by external
logic.
The board’s specifications are:
•
Input Voltage: 3V to 5.5V
•
Output Voltages: 1.2V
OUT1
and 2.5V
OUT2
•
Maximum load current: 2A/output
•
Minimum load current: 0A
•
Size: 1.35 in. × 1.6 in.
•
Peak Current Limit:
≊
3.2A at 25°C
•
Nominal Switching Frequency: 550 kHz or 2.2MHz
2
Powering Up the Board
Since the EN pins are directly tied to the input voltage via jumpers J
1
and J
2
, starting up the board is as
simple as connecting a voltage supply from 3V to 5.5V between the V
IN
and GND terminals. There should
be 1.2V on V
OUT1
and 2.5V on V
OUT2
, assuming the jumpers connect V
IN
to EN for each channel. Great
care should be taken in powering up the supplies such that the input voltage, V
IN
, does not exceed the
Absolute Maximum Rating of 7V. If the part experiences voltages greater than 7V for a prolonged period
of time, then damage to the part can occur and then the evaluation board may cease working.
The linear soft-start ramps for the two output voltages and should last about 600 µs. Load can be applied
prior to power-up. If an output is shorted either before or after start-up, removal of the short-circuit
condition should bring the corresponding output back to normal voltage.
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1
SNVA353B – February 2009 – Revised April 2013
AN-1870 LM26420 Evaluation Board
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