MAX791CPE+ Maxim Integrated Products, MAX791CPE+ Datasheet - Page 15
![IC MPU SUPERVISORY CIRCUIT 16DIP](/photos/6/57/65728/175-16-dip_sml.jpg)
MAX791CPE+
Manufacturer Part Number
MAX791CPE+
Description
IC MPU SUPERVISORY CIRCUIT 16DIP
Manufacturer
Maxim Integrated Products
Type
Battery Backup Circuitr
Datasheet
1.MAX791CSE.pdf
(19 pages)
Specifications of MAX791CPE+
Number Of Voltages Monitored
1
Output
Push-Pull, Totem Pole
Reset
Active Low
Reset Timeout
140 ms Minimum
Voltage - Threshold
4.65V
Operating Temperature
0°C ~ 70°C
Mounting Type
Through Hole
Package / Case
16-DIP (0.300", 7.62mm)
Monitored Voltage
4.65 V
Undervoltage Threshold
4.5 V
Overvoltage Threshold
4.75 V
Manual Reset
Resettable
Watchdog
Yes
Battery Backup Switching
Yes
Power-up Reset Delay (typ)
280 ms
Supply Voltage (max)
5.5 V
Supply Voltage (min)
0 V
Supply Current (typ)
150 uA
Maximum Power Dissipation
842 mW
Mounting Style
Through Hole
Maximum Operating Temperature
+ 70 C
Chip Enable Signals
Yes
Minimum Operating Temperature
0 C
Output Type
Active Low or Open Drain or Push-Pull
Power Fail Detection
Yes
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
The power-fail comparator can be used to monitor a
negative supply voltage using Figure 15’s circuit. When
the negative supply is valid, PFO is low. When the neg-
ative supply voltage drops, PFO goes high. This cir-
cuit’s accuracy is affected by the PFI threshold toler-
ance, the V
The backup battery may be disconnected while V
above the reset threshold. No precautions are neces-
sary to avoid spurious reset pulses.
While issuing resets to the µP during power-up, power-
down, and brownout conditions, these supervisors are
relatively immune to short-duration negative-going V
transients (glitches). It is usually undesirable to reset
the µP when V
Figure 16 shows maximum transient duration vs. reset
comparator overdrive, for which reset pulses are not
generated. The graph was produced using negative-
Figure 13. Alternate CE Gating
*MAXIMUM Rp VALUE DEPENDS ON
THE NUMBER OF RAMs.
MINIMUM Rp VALUE IS 1kΩ
CC
CE IN
CC
voltage, and resistors R1 and R2.
Negative-Going V
MAX791
Monitoring a Negative Voltage
V
GND
Backup-Battery Replacement
experiences only small glitches.
OUT
______________________________________________________________________________________
CE OUT
Rp*
ACTIVE-HIGH CE
LINES FROM LOGIC
Microprocessor Supervisory Circuit
CC
Transients
CE
CE
CE
CE
CE
CE
CE
CE
RAM 1
RAM 2
RAM 3
RAM 4
CC
CC
is
going V
reset threshold by the magnitude indicated (reset com-
parator overdrive). The graph shows the maximum
pulse width that a negative-going V
typically have without causing a reset pulse to be
issued. As the amplitude of the transient increases (i.e.,
goes farther below the reset threshold), the maximum
allowable pulse width decreases. Typically, a V
sient that goes 100mV below the reset threshold and
lasts for 40µs or less will not cause a reset pulse to be
issued.
A 100nF bypass capacitor mounted close to the V
pin provides additional transient immunity.
SWT is internally connected to a ±100nA current
source. When a capacitor is connected from SWT to
ground (to select an alternative watchdog-timeout peri-
od), the current source charges and discharges the
timing capacitor to create the oscillator that controls the
watchdog-timeout period. To prevent timing errors or
oscillator start-up problems, minimize external current
leakage sources at this pin, and locate the capacitor as
Figure 14. Adding Hysteresis to the Power-Fail Comparator
PFO
+5V
R2
R1
0V
Connecting a Timing Capacitor to SWT
V IN
0V
CC
V
V
TRIP
H
pulses, starting at 5V and ending below the
= 1.25 /
R3
= 1.25 R1 + R2
TO µP
R1 + R2
C1*
R2
R2
||
R3
||
R3
PFI
PFO
VL - 1.25 + 5 - 1.25 = 1.25
V
MAX791
L
R1
GND
+5V
V
V
CC
TRIP
V
IN
CC
V
H
R3
transient may
*OPTIONAL
R2
CC
tran-
CC
15