Datasheet

TC1303A/TC1303B/TC1303C/TC1304
DS21949C-page 22 © 2008 Microchip Technology Inc.
4.4 Power-Good
A Power-Good (PG) output signal is generated based
off of the buck regulator output voltage (V
OUT1
), the
LDO output voltage (V
OUT2
) or the combination of both
outputs. A fixed delay time of approximately 262 ms is
generated once the monitored output voltage is above
the power-good threshold (typically 94% of V
OUTX
). As
the monitored output voltage falls out of regulation, the
falling PG threshold is typically 92% of the output
voltage. The PG output signal is pulled up to the output
voltage, indicating that power is good and pulled low,
indicating that the output is out of regulation. The
typical quiescent current draw for power-good circuitry
is less than 10 µA.
If the monitored output voltage falls below the power-
good threshold, the power-good output will transition to
the Low state. The power-good circuitry has a 165 µs
delay when detecting a falling output voltage. This
helps to increase the noise immunity of the power-good
output, avoiding false triggering of the PG signal during
line and load transients.
FIGURE 4-1: Power-Good Timing.
4.5 Power Good Output Options
There are three monitoring options for the TC1303
family.
For the TC1303A, only the buck regulator output
voltage (V
OUT1
) is monitored. The PG output signal
depends only on V
OUT1
.
For the TC1303B, only the LDO output voltage (V
OUT2
)
is monitored. The PG output signal depends only on
V
OUT2
.
For the TC1303C and TC1304, both the buck regulator
output voltage and LDO output voltage are monitored.
If either one of the outputs fall out of regulation, the PG
will be low. Only if both V
OUT1
and V
OUT2
are within the
PG voltage threshold limits will the PG output be high.
For the TC1303A,C and TC1304, the PG output pin is
open drain and can be pulled up to any level within the
given absolute maximum ratings (A
GND
- 0.3V) to (V
IN
+ 0.3V).
TABLE 4-1: PG AVAILABLE OPTIONS
t
RPU
t
RPD
V
TH_H
V
OUT1
PG
V
OL
V
OH
or V
OUT2
Part
Number
PG Output
Buck
(V
OUT1
)
PG
Output
LDO
(V
OUT2
)
PG Output
Type
TC1303A Yes No Open-Drain
TC1303B No Yes Push-Pull
(V
OUT2
)
TC1303C Yes Yes Open-Drain
TC1304 Yes Yes Open-Drain