Texas Instruments TPS6420xEVM-023, Руководство пользователя

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Modifications
1-3 Introduction
-
Large inductor area under removable solder mask
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Extra input and output capacitor pads
-
Resistors R6 and R7 can be left open and R5 can be shorted (by a 0
Ω
resistor) to allow current sensing by Q1’s r
DS(on)
.
-
Resistor R8 and capacitor C7 can be populated to provide an RC snubber
which dampens the oscillations and resulting EMI produced at the switch
node when the device operates in discontinuous mode.
-
The TPS6420x family of devices work best using an output capacitor with
between 50 to 150 m
Ω
of ESR. However, they will work with low ESR ce-
ramic output capacitors if a large resistor is placed from the SW node to
the FB node as explained on the last page of the datasheet application
section. Resistor R8 can be used as this large resistor since one side al-
ready connects to the SW node, if the other side is manually connected
to the FB node using a small wire.
Changing components can improve or degrade EVM performance. For
example, using a FET with higher r
DS(on)
and/or an inductor with larger dc
resistance will lower the efficiency of the solution. In addition, using a FET in
a larger package with larger gate capacitance will likely lower efficiency since
the TPS6420x’s gate drive limited to 150 mA, would have difficulty driving a
larger gate capacitance.