Low-Cost, µP Supervisory Circuits
______________________________________________________________Pin Description
PIN
MAX705/MAX706 MAX707/MAX708
MAX813L
NAME
FUNCTION
DIP/SO
µMAX
DIP/SO
µMAX
DIP/SO
µMAX
Manual-Reset Input triggers a reset pulse when
pulled below 0.8V. This active-low input has an inter-
nal 250µA pull-up current. It can be driven from a TTL
or CMOS logic line as well as shorted to ground with
a switch.
1
3
1
3
1
3
MR
V
2
3
4
5
2
3
4
5
2
3
4
5
+5V Supply Input
CC
GND
0V Ground Reference for all signals
Power-Fail Voltage Monitor Input. When PFI is less
than 1.25V, PFO goes low. Connect PFI to GND or
4
5
6
7
4
5
6
7
4
5
6
7
PFI
V
when not used.
CC
Power-Fail Output goes low and sinks current when
PFI is less than 1.25V; otherwise PFO stays high.
PFO
Watchdog Input. If WDI remains high or low for
1.6sec, the internal watchdog timer runs out and
WDO goes low (Figure 1). Floating WDI or connect-
ing WDI to a high-impedance three-state buffer dis-
ables the watchdog feature. The internal watchdog
timer clears whenever reset is asserted, WDI is three-
stated, or WDI sees a rising or falling edge.
6
-
8
-
-
-
-
6
-
8
-
WDI
N.C.
6
7
No Connect
Active-Low Reset Output pulses low for 200ms when
triggered, and stays low whenever V is below the
CC
reset threshold (4.65V in the MAX705 and 4.40V in the
7
1
1
-
-
RESET
MAX706). It remains low for 200ms after V rises
CC
above the reset threshold or MR goes from low to high
(Figure 3). A watchdog timeout will not trigger RESET
unless WDO is connected to MR.
Watchdog Output pulls low when the internal watch-
dog timer finishes its 1.6sec count and does not go
high again until the watchdog is cleared. WDO also
goes low during low-line conditions. Whenever V is
below the reset threshold, WDO stays low; however,
unlike RESET, WDO does not have a minimum pulse
CC
8
2
-
-
8
7
2
1
WDO
width. As soon as V rises above the reset thresh-
CC
old, WDO goes high with no delay.
Active-High Reset Output is the inverse of RESET.
Whenever RESET is high, RESET is low, and vice
versa (Figure 2). The MAX813L has a RESET output
only.
-
-
8
2
RESET
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5
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
