MAX791 Maxim, MAX791 Datasheet - Page 7

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

______________________________________________________________Pin Description
PIN
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
–
L
—
BATT ON
–
C
O
—
VBATT
–
R
–
W
NAME
—
—
– –
C
V
–
W
GND
E
—
SWT
—
–
P
W
WDI
–
V
—
E
—
PFI
–
M
—
OUT
— —
E
D
—
–
F
—
CC
—
D
S
OUT
—
L
—
—
R
P
O
—
–
—
IN
E
O
–
—
I
–
O
N
T
—
–
–
E
–
Output Supply Voltage. V
threshold. When V
Connect a 0.1µF capacitor from V
Input Supply Voltage—+5V input
the base of a PNP through a current-limiting resistor to BATT ON for V
250mA.
Power-Fail Output. This is the output of the power-fail comparator.
Set Watchdog-Timeout Input. Connect this input to V
Connect a capacitor between this input and GND to select another watchdog-timeout period. Watchdog-timeout
period = 2.1 x (capacitor value in nF) ms.
Manual-Reset Input. This input can be tied to an external momentary pushbutton switch, or to a logic gate out-
put.
–
L
erate an NMI if the unregulated supply is inaccessible.
Watchdog Input. WDI is a three-level input. If WDI remains either high or low for longer than the watchdog time-
out period,
the watchdog function. WDI connects to an internal voltage divider between V
supply when left unconnected.
Chip-Enable Output.
low when reset is asserted,
Chip-Enable Input. The input to chip-enable gating circuit. Connect to GND or V
Watchdog Output.
–
W
when
–
R
after V
Watchdog-Pulse Output. Upon the absence of a transition at WDI,
–
W
Backup-Battery Input. Connect to external battery or capacitor and charging circuit.
Ground. 0V reference for all signals
Battery On Output. Goes high when V
This is an uncommitted comparator, and has no effect on any other internal circuitry.
Power-Fail Input. This is the noninverting input to the power-fail comparator. When PFI is less than 1.25V,
–
P
—
—
—
_______________________________________________________________________________________
—
—
F
O
—
E
—
—
D
D
—
—
O
S
W
—
–
O
P
— —
—
–
E
–
R
—
—
goes low. Connect PFI to GND or V
O
L
—
–
T
–
—
E
returns high on the next transition at WDI.
–
R
—
I
—
CC
N
S
precedes
—
—
E
Output goes low whenever V
—
E
E
–
S
—
—
crosses the reset threshold on power-up.
–
T
E
—
Output goes low when V
–
W
T
–
remains low as long as
—
D
is asserted.
—
Microprocessor Supervisory Circuit
O
–
– –
W
goes low.
CC
—
–
W
D
—
—
O
D
–
C
—
–
falls below VBATT and V
—
O
E
–
–
by 70ns.
OUT goes low only when
goes low if WDI remains either high or low longer than the watchdog timeout period.
OUT
–
W
–
C
—
—
E
D
–
connects to V
—
O
OUT will stay low for 15µs or until
–
remains low until the next transition at WDI. Leaving WDI unconnected disables
OUT
CC
–
M
—
CC
R
OUT
–
to GND.
falls to 150mV above the reset threshold. The output can be used to gen-
is held low and for 200ms after
falls below the reset threshold.
OUT
switches to VBATT. Goes low when V
CC
when not used.
CC
when V
–
W
—
is below the reset threshold, V
D
FUNCTION
– –
C
—
—
O
E
–
–
OUT
IN is low and V
remains high if WDI is unconnected.
CC
to select the default 1.6sec watchdog timeout period.
is greater than VBATT and V
–
C
–
W
—
—
–
P
—
E
–
D
F
—
—
IN goes high, whichever occurs first.
CC
P
O
—
OUT
–
O
–
M
–
R
–
—
goes low when PFI is less than 1.25V.
—
is above the reset threshold. If
E
R
—
will pulse low for a minimum of 1ms.
–
S
—
current requirements greater than
returns high.
E
—
T
–
OUT
will remain low for typically 200ms
OUT
OUT
OUT
and GND, which sets it to mid-
switches to V
connects to VBATT.
if not used.
CC
is above the reset
–
W
—
D
—
O
–
is also high
CC
. Connect
–
C
—
E
–
IN is
7