ILC705 Datasheet, PDF (4/5 Pages) Impala Linear Corporation – MP SUPERVISORY CIRCUIT

mP Supervisory Circuit
Circuit Description
Microprocessor Reset
The RESET pin is asserted whenever V_CC falls below the
reset threshold voltage or when MR goes low. The reset pin
remains asserted for a period of 200ms after V_CC has risen
above the reset threshold voltage and MR goes high. The
reset function ensures the microprocessor is properly reset
and powers up into a known condition after a power failure.
RESET will remain valid with V_CC as low as 1.4V
fail comparator (PFI) can be chosen so as to trip the power
fail comparator a few milliseconds before V_CC falls below
the maximum reset threshold voltage. The output of the
power fail comparator (PFO) can be used to interrupt the
microprocessor when used in this mode and execute shut-
down procedures prior to power loss
VCC
tMR
MR
tMD
tRS
RESET
VRT
tRS
Unregulated DC
R1
PFI
4
+
R2
1.25 V
-
5 PFO
WDO
Watchdog Timer
The microprocessor can be monitored by connecting the
WDI pin (watchdog input) to a bus line or I/O line. If a tran-
sition does not occur on the WDI pin within the watchdog
timeout period, then WDO will go low. A minimum pulse of
50ns or any transition low-to-high or high-to-low on the WDI
pin will reset the watchdog timer. The output of the watch-
dog timer (WDO) will remain high if WDI sees a valid tran-
sition within the watchdog timeout period or if WDI is left
floating. If V_CC falls below the reset threshold voltage then
WDO goes low immediately regardless of WDI. If WDI is left
floating, then WDO can be used as a low line indicator.
Manual Reset
The manual-reset input (MR) allows reset to be triggered by
a pushbutton switch which is debounced by the 140ms min-
imum reset pulse width. MR can be driven by external
TTL/CMOS compatible logic. By connecting WDO to MR a
watchdog timeout will generate a reset pulse in the
ILC705/ILC706.
Power Fail Warning
An additional comparator which is independent of other
functions on the ILC705/706/707/708 is provided for early
warning of power failure. An external voltage divider can be
used to compare unregulated DC to an internal 1.25V ref-
erence. The voltage divider ratio on the input of the power
Alternate Reference Guide
Industry P/N
MAX705CPA
MAX705CSA
MAX705EPA
MAX705ESA
ADM705AN
DS1705
MAX706CPA
MAX706CSA
MAX706EPA
MAX706C/D
ADM706AN
DS1706
MAX707CPA
MAX707CSA
MAX707EPA
MAX707ESA
MAX707C/D
ADM707AN
DS1707
MAX708CPA
MAX708CSA
MAX708EPA
MAX708ESA
MAX708C/D
ADM708AN
DS1708
ILC Direct
Replacement
ILC705N
ILC705M
ILC705N
ILC705M
ILC705N
ILC705
ILC706N
ILC706M
ILC706N
ILC706D
ILC706N
ILC706
ILC707N
ILC707M
ILC707N
ILC707M
ILC707D
ILC707N
ILC707
ILC708N
ILC708M
ILC708N
ILC708M
ILC708D
ILC708N
ILC708
Impala Linear Corporation
ILC705-708 1.0
[phone] www.impalalinear.com
Sept 1999 4