Datasheet

3
SST
SST
SS
SS
10
4.1V
V
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TPS40200-EP
SGLS371A –JANUARY 2007–REVISED JANUARY 2013 www.ti.com
Soft-Start Capacitor
The soft-start interval is given (in pF) by:
(18)
Where:
R = Internal 105-kΩ charging resistor
V
CC
= Input voltage up to 8 V, where the charging voltage is internally clamped to 8 V maximum
V
OS
= 700 mV and, because the input voltage is 12 V, V
SST
= 8 V
The oscilloscope output (see Figure 36) shows the expected delay at the output (middle trace) until the soft-start
node (bottom trace) reaches 700 mV. At this point, the output rises following the exponential rise of the soft-start
capacitor voltage until the soft-start capacitor reaches 1.4 V and the internal 700-mV reference takes over. This
total time is approximately 1 ms, which agrees with the calculated value of 0.95 ms where the soft-start
capacitance is 0.047 μF.
A. Channel 1 is the output voltage rising to 3.3 V.
B. Channel 2 is the soft-start (SS) pin.
Figure 36. Soft Start Showing Output Delay and Controlled Rise to Programmed Output Voltage
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