Datasheet

V =
VB
V + 0.6 V
STC
t
on
V
DDon
V
BUS
V
STC
V
VS
t
off
V
DDoff
V
VDD
V
PF
typical threshold voltage
for power fail PF
TSS721A
SLAS222A –APRIL 1999–REVISED SEPTEMBER 2009................................................................................................................................................ www.ti.com
Power On/Off
Figure 5. Power On/Off Timing
Power Fail Function
Because of the rectifier bridge BR at the input, BUSL1, and BUSL2, the TSS721A is polarity independent. The
pin VB to ground (GND) delivers the bus voltage V
VB
less the voltage drop over the rectifier BR. The voltage
comparator TC2 monitors the bus voltage. If the voltage V
VB
> V
STC
+ 0.6 V, then the output PF = 1. The output
level PF = 0 (power fail) provides a warning of a critical voltage drop to the microcontroller to save the data
immediately.
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