ZHCSJM5D September 2009 – April 2019 TPS61093
PRODUCTION DATA.
The TPS61093 turns on the isolation FET and PWM switch when the EN pin is pulled high. During the soft-start period, the R and C network on the SS pin is charged by an internal bias current of 5 μA (typical). The RC network sets the reference voltage ramp up slope. Because the output voltage follows the reference voltage via the FB pin, the output voltage rise time follows the SS pin voltage until the SS pin voltage reaches 0.5 V. The soft-start time is given by Equation 2.
where
When the EN pin is pulled low to switch the IC off, the SS pin voltage is discharged to zero by the resistor R3. The discharge period depends on the RC time constant. Note that if the SS pin voltage is not discharged to zero before the IC is enabled again, the soft start circuit may not slow the output voltage startup and may not reduce the startup inrush current.