MAX791 Maxim, MAX791 Datasheet - Page 8

• Manufacturer Part Number: MAX791
• Description: Microprocessor Supervisory Circuit
• Manufacturer: Maxim

Microprocessor Supervisory Circuit
Figure 1. Block Diagram
Many µP-based products require manual-reset capabil-
ity, allowing the operator or test technician to initiate a
reset. The Manual Reset Input (MR) can be connected
directly to a switch, without an external pull-up resistor
or debouncing network. It connects to a 1.25V com-
parator, and has a pull-up to V
1. The propagation delay from asserting MR to RESET
asserted is 4µs typical. Pulsing MR low for a minimum
of 15µs resets all the internal counters, sets the
Watchdog Output (WDO) and Watchdog-Pulse Output
8
SWT
WDI
V
_______________Detailed Description
MR
PFI
CC
VBATT
CE IN
_______________________________________________________________________________________
13
11
3
1
9
8
7
V
OUT
4.65V
1.25V
4
150mV
TIMEBASE FOR
CHIP-ENABLE
GENERATION
GND
WATCHDOG
TRANSITION
WATCHDOG
RESET AND
CONTROL
DETECTOR
OUTPUT
RESET
Manual Reset Input
OUT
MAX791
as shown in Figure
WATCHDOG
TIMER
10
LOWLINE
BATT ON
12
15
16
14
5
2
6
V
CE OUT
RESET
WDPO
WDO
PFO
OUT
(WDPO) high, and sets the Set Watchdog-Timeout
(SWT) input to V
ed to V
chip-enable function, setting the Chip-Enable Output
(CE OUT) to a high state. The RESET output remains
active as long as MR is held low, and the reset-timeout
period begins after MR returns high (Figure 2).
Use this input as either a digital-logic input or a second
low-line comparator. Normal TTL/CMOS levels can be
wire-OR connected via pull-down diodes (Figure 3),
and open-drain/collector outputs can be wire-ORed
directly.
Figure 2. Manual-Reset Timing Diagram
Figure 3. Diode "OR" connections allow multiple reset sources
to connect to
SOURCES
CE OUT
OTHER
RESET
RESET
CE IN
* DIODES NOT REQUIRED ON OPEN-DRAIN OUTPUTS
MR
0V
OUT
MANUAL RESET
–
M
(for internal timeouts). It also disables the
—
R
–
.
OUT
- 0.6V, if it is not already connect-
*
*
MR
25 s MIN
MAX791
7.5 s TYP
15 s TYP