IMP802LCPA IMP [IMP, Inc], IMP802LCPA Datasheet - Page 7

• Manufacturer Part Number: IMP802LCPA
• Description: ?P POWER SUPPLY SUPERVISOR WITH BATTERY BACKUP SWITCH
• Manufacturer: IMP [IMP, Inc]

Backup Power Sources - SuperCap
Capacitor storage, with very high values of capacitance, can be
used as a back-up power source instead of batteries. SuperCap
are capacitors with capacities in the fractional farad range. A 0.1
farad SuperCap
Like the battery supply, it is important that the capacitor voltage
remain below the maximum voltages shown in Table 2. Although
the circuit of Figure 5 shows the most simple way to connect the
SuperCap
tion will not occur since the capacitor will ultimately charge up to
V
the circuit of Figure 6 is preferred. In this circuit configuration, the
diode-resistor pair clamps the capacitor voltage at one diode-
drop below V
5V for the IMP692A/802M or within
IMP690A/802L/805L to insure that the storage capacitor does not
achieve an overvoltage state.
Note: SuperCap
CC
Figure 6. Capacitor as back-up Power Source - Voltage
. To insure that an overvoltage condition does not occur,
+5V
Figure 5. Capacitor as a backup power source
100k
TM
+
+5V
, this circuit cannot insure that an overvoltage condi-
CC
( ) IMP805L
0.1F
+
TM
TM
. V
( ) IMP805L
clamped to 0.5V below V
would provide a useful backup power source.
is a trademark of Baknor Industries
CC
0.1F
V
V
CC
BATT
itself should be regulated within 5% of
V
V
GND
CC
BATT
(RESET)
IMP802M
IMP692A
RESET
GND
V
OUT
RESET
V
OUT
To Static RAM
To P
10% of 5V for the
TM
CC
690A_07.eps
To Static RAM
To P
690A_08.eps
IMP690A
IMP690A
TM
Operation Without a Backup Power Source
When operating without a back-up power source, the V
should be connected to GND and V
V
V
of the PMOS switch.
Power-Fail Comparator
The Power Fail feature is an independent voltage monitoring
function that can be used for any number of monitoring activities.
The PFI function can provide an early sensing of power supply
failure by sensing the voltage of the unregulated DC ahead of
the regulated supply sensing seen by the backup-battery
switchover circuitry.
The PFI pin is compared to a 1.25V internal reference. If the volt-
age at the PFI pin is less than this reference voltage, the PFO pin
goes low. By sensing the voltage of the raw DC power supply, the
microprocessor system can prepare for imminent power-loss,
especially if the battery backup supply is not enabled. The input
voltage at the PFI pin results from a simple resistor voltage
divider as shown in Figure 7.
CC
OUT
, since power source switchover will not occur. Connecting
Figure 7. Simple Voltage divider sets PFI trip point
to V
, 692A
, 692A
CC
PFO
eliminates the voltage drop due to the ON-resistance
+5V
0V
A
+5V
R
R
R
1
2
5
1
R
R
, 802L, 802M, 805L
2
, 802L, 802M, 805L
2
A
V
PFI
CC
1 25
.
Application Information
IMP802M
IMP690A
IMP692A
IMP802L
IMP805L
V
GND
B
OUT
B
R
PFO
5
1
should be connected to
R
R
2
2
690A_09.eps
1 25
.
V
BATT
pin
7