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Notice: The information in this document is subject to change without notice

ASM690A / 692A

ASM802L / 802M

ASM805L

µP Power Supply Supervisor With Battery Backup Switch

rev 1.0

October 2003

Backup Power Sources - Batteries

Battery voltage selection is important to insure that the

battery does not discharge through the parasitic device diode

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

pin will not cause a powersupply switchover as can occur in

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.

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

insure that an over voltage condition does not occur, the

circuit of Figure 5 is preferred. In this circuit configuration, the

diode-resistor pair clamps the capacitor voltage at one diode

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.

Part Number

MAXIMUM Battery Voltage

ASM690A

4.80

ASM802L

4.80

ASM805L

4.80

ASM692A

4.55

ASM802M

4.55

100K

ASM692A

ASM802M

RESET

(RESET)

GND

To µP

+

0.1F

Figure 5: Capacitor as a backup power source

RESET

(RESET)

GND

To µP

+5V

0.1F

+

Figure 4: Capacitor as a backup power source

D2

D1

D1

ASM692A

ASM802M

+5V