SP6656_06 Datasheet, PDF (13/16 Pages) Sipex Corporation – High Efficiency 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output

APPLICATION INFORMATION
The output voltage is programmed by the external divider, as shown in the typical
application circuit on Page 1. Depending on the topology used, 1 or 2 voltages ,V_OUT
is set as follows:
1) Single V
OUT
First pick a value for RI that is no larger than
300KΩ. Too large a value of RI will reduce the
AC voltage seen by the loop comparator since
the internal FB pin capacitance can form a low
pass filter with RF in parallel with RI. The
formula for RF with a given RI and output
voltage is:
R_F = (V_OUT / 0.8V - 1) _* (R_I)
V_OUT
VO
CF
R_F
22pF
FB
R_I
2) Dual V_OUT (selectable)
First pick the lowest voltage that will be used
and utilize the same method as above.
R_F = (V_{OUT_LOW}/ 0.8V - 1) _* (R_I) R_I≤ 300kΩ
Then use the following equation to determine
R_S:
[R_I//R_S] = ^{0.8 * RF .}
V_{OUT_HIGH} - 0.8
R_{S =}
[RI//RS] .
{ } ^{1 -}
[RI//RS]
R_I
V_OUT
VO
R_F
CF
22pF
FB
R_S
R_I
OVSO
Date: 3/6/06
SP6656, 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output
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© Copyright 2006 Sipex Corporation