Datasheet

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SLUS589B− NOVEMBER 2003 − REVISED FEBRUARY 2005
13
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APPLICATION INFORMATION
Figure 8 shows startup waveforms of a 1.2-V V
OUT
voltage under different pre-bias scenarios. The first trace
is when the output voltage starts with zero pre−bias. The second and third traces, respectively, the pre-bias
levels are 0.5 V and 1.0 V.
t − Time − 2 µs/div
V
HDRV
V
LDRV
Figure 7.
MOSFET Drivers at Beginning of Soft-Start
t − Time − 500 µs/div
Figure 8.
Startup Waveforms
V
IN
= 5 V
V
OUT
= 1.2 V
(200 mV/div)
PREBIAS = 0 V
PREBIAS = 0.5 V
PREBIAS = 1 V
The recommended V
OUT
voltage pre-bias range is less than or equal to 90% of final regulation. That is, a
pre-bias level between 90% and 100% of final regulation could lead to sinking the pre-bias supply. If the V
OUT
voltage is initially set to higher than 100% of final regulation, the controller forces sinking current at the end of
soft-start in order to bring the output quickly into regulation.
The following pages include design ideas for a few applications. For more ideas, detailed design information,
and helpful hints, visit the TPS40000 resources at http://power.ti.com.