Datasheet

( )
+
= ´
OUT REF
R1 R2
V V
R2
( )
+
= ´
OUT SS(EAMP)
R1 R2
V V
R2
UDG-09203
t – Time
Internal Logic RUN
Clamped at VDD
0.5 V
V
REF
= 0.6 V
SS
SS_EAMP
t
SS
0.65 V
t
CAL
1.1 V
V
SS
V
COMP
V
VALLEY
V
OUT
(1)
(2)
TPS40170
SLUS970A –MARCH 2011–REVISED NOVEMBER 2013 www.ti.com
The SS pin is discharged through an internal switch during the following conditions:
• Input (VIN) undervoltage lock out UVLO pin less than V
UVLO
• Overcurrent protection calibration time (t
CAL
)
• VBP less than threshold voltage (V
BP(off)
)
Because it is discharged through an internal switch, the discharging time is relatively fast compared with the
discharging time during the fault restart which is discussed in the Soft-start During Overcurrent Fault section.
Figure 21. Soft-Start Waveforms
NOTE
Referring to Figure 21
• (1) VREF dominates the positive input of the error amplifier
• (2) SS_EAMP dominates the positive input of the error amplifier
For 0 < V
SS_EAMP
< V
REF
(8)
For V
SS_EAMP
> V
REF
(9)
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