SMH4803
ENPGA (16)
test all combinations (all 128 possibilities) are readily
The ENPGA input controls the PG2# and PG3# outputs. available as off the shelf stock items.
When ENPGA is pulled low, the PG2# output is immedi-
atelyplacedinahighimpedancestate.IfENPGAisdriven
high, thenthePG2#outputwillimmediatelybedrivenlow,
Power Good Delay
The PG delay timer that controls the delay from PG1# to
PG2# and PG2# to PG3# being asserted can be set to
typical values of 5ms, 20ms, 80ms or 160ms.
provided PG1# has been active for at least tPGD
.
PG3# (17)
Quick-Trip Circuit Breaker Threshold
The Quick-Trip circuit breaker threshold can be set to
200mV, 100mV, 60mv or OFF. This is the threshold
voltage drop across RS that is placed between VSS and
CBSense.
PG3# is an open drain active low output with no internal
pull-up. PG3# is the last power good signal to be enabled
after Vgate, PG1# and PG2# have been turned on. PG3#
is delayed PGD after PG2# is active and 2xPGD after
PG1# is active. PG3# can be used to switch a third load
or a DC/DC converter.
Circuit Breaker Delay
The circuit breaker delay defines the period of time the
voltagedropacrossRS isgreaterthan50mVbutlessthan
VQCB before the Vgate output will be shut down. This is
effectivelyafiltertopreventspuriousshutdownsofVgate.
Thedelaysthatcanbeprogrammedare5µs, 50µs, 150µs
and 400µs.
PG1# (18)
PG1# is an open drain active low output with no internal
pull-up. PG1# is enabled after Vgate is enabled and
voltage across the load is within spec. PG1# can be used
to switch a load or enable a DC/DC converter.
PG2# (19)
Pin Detect
PG2# is an open drain active low output with no internal
pull-up.PG2#isenabledafterVgateandPG1#havebeen
turned on. PG2# is delayed PGD after PG1# is active.
PG2# can be used to switch a second load or a DC/DC
converter.
The Pin Detect function can be enabled or disabled.
VDD (20)
VDD is the positive supply connection. An internal shunt
regulator connected between VDD and VSS develops
approximately 12 volts that supplies the SMH4803. A
resistor must be placed in series with the VDD pin to limit
the regulator current (RD in the application illustrations).
PROGRAMMABLE FEATURES
Because the SMH4803 is electrically programmable it
can be fine-tuned for a wide variety of applications prior to
shipmenttothecustomer.Becauseofthisamanufacturer
can use a common part type across a wide range of
boards that are used on a common host but have different
electrical loads, power-on timing requirements, host volt-
age monitoring needs etc.
This ability to use a common solution across many plat-
forms shifts the focus of design away from designing a
new power interface for each board to concentrating on
the value added back-end logic.
Because the programming of the features is done at final
SUMMIT MICROELECTRONICS
2041 8.4 6/15/00
9
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
