Datasheet

UDG-09213
PGOOD1
V
IN
R2
V
OUT1
R1
SS2
V
IN
R4
V
OUT2
R3
POL1
POL2
C
SS
0
Voltage
V
SS2
, V
PGOOD1
V
OUT1
V
OUT2
V
PGOOD2
t – Time
UDG-09214
TPS40170
SLUS970A –MARCH 2011–REVISED NOVEMBER 2013 www.ti.com
Sequential startup is shown in Figure 31. During start-up of the first module, POL1, its PGOOD1 is pulled to low.
Since PGOOD1 is connected to soft-start SS2 of the second module, POL2, is not able to charge its soft-start
capacitor. After output voltage VOUT1 of POL1 reaches its setting point, PGOOD1 is released. POL2 starts
charging its soft-start capacitor. Finally, output voltage V
OUT2
of POL2 reaches its setting point.
Figure 31. Sequential Start-Up Schematic Figure 32. Sequential Start-Up Waveform
NOTE
The TRK pin has high impedance, so it is a noise sensitive terminal. If the tracking
function is used, a small R-C filter is recommended at the TRK pin to filter out high-
frequency noise.
If the tracking function is not used, the TRK pin must be pulled up directly or through a
resistor (with a value between 10 kΩ and 100 kΩ) to VDD.
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