MAX807L View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX807L Datasheet PDF : 16 Pages
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Full-Featured µP Supervisory Circuit with
±1.5% Reset Accuracy
R1
VCC
PFI MAX807 PFO
R2
GND
VIN
R1
R2
VCC
PFI MAX807 PFO
MR
GND
VCC
VIN
VCC
PFO
PFO
VL VTRIP
0V
VIN
VIN
VTRIP VH
( ) VTRIP = R2 (VPFT + VPFH)
1 +1
R1 R2
– VCC
R1
WHERE VPFT = 2.265V
( ) R1 + R2
VTRIP = VPFT R2
( ) VL = R2 (VPFT)
1 +1
R1 R2
– VCC
R1
a)
VPFH = 20mV
NOTE: VTRIP, VL ARE NEGATIVE.
b)
( ) R1 + R2
VH = (VPFT + VPFH) R2
Figure 10. Using the Power-Fail Comparator to Monitor an Additional Power Supply: a) VIN is Negative, b) VIN is Positive
FROM
REGULATED
SUPPLY
0.1µF
VCC
OUT
MAX807
BATT
RESET
LOW LINE
WDI
GND
a)
0.1µF
µP POWER
POWER TO
CMOS RAM
µP
2.8V
RESET
NMI
I/O LINE
VOLTAGE
REGULATOR
VCC
OUT
0.1µF
MAX807
BATT
RESET
PFI
PFO
WDI
GND
0.1µF
µP POWER
POWER TO
CMOS RAM
µP
2.8V
RESET
NMI
I/O LINE
Power-Fail Comparator
PFI is the noninverting input to an uncommitted com-
parator. If PFI is less than VPFT (2.265V), PFO goes low.
The power-fail comparator is intended to monitor the
preregulated input of the power supply, providing an
early power-fail warning so software can conduct an
orderly shutdown. It can also be used to monitor sup-
plies other than 5V. Set the power-fail threshold with a
resistor-divider, as shown in Figure 10.
Power-Fail Input
PFI is the input to the power-fail comparator. The typical
comparator delay is 14µs from VIL to VOL (power failing),
and 32µs from VIH to VOH (power being restored). If
unused, connect this input to ground.
Power-Fail Output
The Power-Fail Output (PFO) goes low when PFI goes
below VPFT. It typically sinks 3.2mA with a saturation
voltage of 0.1V. With PFI above VPFT, PFO is actively
pulled to VCC. Connecting PFI through a voltage-
divider to a preregulated supply allows PFO to gener-
ate an NMI as the preregulated power begins to fall
(Figure 11b). If the preregulated supply is inaccessible,
use LOW LINE to generate the NMI (Figure 11a). The
LOW LINE threshold is typically 52mV above the reset
threshold (see the Low-Line Comparator section).
b)
Figure 11. a) If the preregulated supply is inaccessible, LOW
LINE generates the NMI for the µP. b) Use PFO to generate the
µP NMI if the preregulated supply is accessible.
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