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VDD.
Gate drive output for the low-side synchronous rectifier N-channel MOSFET
Soft-start and overcurrent fault shutdown times are set by charging and discharging a capacitor connected to this pin.
A closed loop soft-start occurs when the internal 3-碌A(chǔ) current source charges the external capacitor from 0.17 V to
0.70 V. During the soft-start period, the current sink capability of the TPS40001 and TPS40003 is disabled. When the
SS/SD voltage is less than 0.12 V, the device is shutdown and the HDRV and LDRV are driven low. In normal opera-
tion, the capacitor is charged to 1.5 V. When a fault condition is asserted, the HDRV is driven low, and the LDRV is
driven high. The soft-start capacitor goes through six charge/discharge cycles, restarting the converter on the seventh
cycle.
Connect to the switched node on the converter. This pin is used for overcurrent sensing in the topside N-channel
MOSFET, zero current sensing in synchronous rectifier N-channel MOSFET, and level sensing for predictive delay
circuit. Overcurrent is determined, when the topside N-channel MOSFET is on, by comparing the voltage on SW with
respect to VDD and the voltage on the ILIM with respect to VDD. Zero current is sensed, when the rectifier N-channel
MOSFET is on, by measuring the voltage on SW with respect to ground. Zero current sensing applies to the
TPS40000/2 devices only.
Power input for the chip, 5.5-V maximum. Decouple close to the pin with a low-ESR capacitor, 1-碌F or larger.
ILIM
1
I
LDRV
6
O
SS/SD
4
I
SW
8
O
VDD
7
I
6
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