ASM802LAEPA ALSC [Alliance Semiconductor Corporation], ASM802LAEPA Datasheet - Page 5

• Manufacturer Part Number: ASM802LAEPA
• Description: UP Power Supply Supervisor With Battery Backup Switch
• Manufacturer: ALSC [Alliance Semiconductor Corporation]

October 2003
Backup Power Sources - Batteries
Battery voltage selection is important to insure that the
battery does not discharge through the parasitic device diode
D1 (see Figure 3) when V
V
Table 2: Maximum Battery Voltages
Although most batteries that meet the requirements of Table
2 are acceptable, lithium batteries are very effective backup
source due to their high-energy density and very low self-
discharge rates.
Battery replacement while Powered
Batteries can be replaced even when the device is in a
powered state as long as V
threshold voltage V
pin will not cause a powersupply switchover as can occur in
some other supervisory circuits. If V
should be grounded.
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
farad range. A 0.1 farad SuperCap™ would provide a useful
backup power source. 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 4
shows the most simple way to connect the SuperCap™, this
circuit cannot insure that an over voltage condition will not
occur since the capacitor will ultimately charge up to V
insure that an over voltage condition does not occur, the
circuit of Figure 5 is preferred. In this circuit configuration, the
rev 1.0
RT
Part Number
ASM802M
ASM690A
ASM692A
.
ASM802L
ASM805L
™
are capacitors with capacities in the fractional
RT
MAXIMUM Battery Voltage
. In the ASM devices, a floating V
µP Power Supply Supervisor With Battery Backup Switch
CC
is less than V
CC
Notice: The information in this document is subject to change without notice
remains above the reset
4.80
4.80
4.80
4.55
4.55
BATT
is not used, the pin
BATT
and V
CC
CC
BATT
. To
>
diode-resistor pair clamps the capacitor voltage at one diode
drop below V
5V for the ASM692A/802M or within ±10% of 5V for the
ASM690A/802L/805L to insure that the storage capacitor
does not achieve an over voltage state.
Note: SuperCap
100K
Figure 5: Capacitor as a backup power source
Figure 4: Capacitor as a backup power source
D1
+
+5V
+5V
D1
0.1F
D2
CC
Voltage clamped to 0.5V below V
. V
TM
+
CC
is a trademark of Baknor Industries
0.1F
V
V
itself should be regulated within ±5% of
CC
BATT
ASM802M
ASM692A
GND
V
V
CC
BATT
(RESET)
ASM690A / 692A
ASM802L / 802M
ASM802M
ASM692A
RESET
V
OUT
GND
(RESET)
RESET
V
OUT
ASM805L
To
To µP
SRAM
CC
To
To µP
5 of 13
SRAM