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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

Watchdog Input

As discussed in the Reset section, the Watchdog input is

used to monitor microprocessor activity. It can be used to

insure that the microprocessor is in a continually responsive

state by requiring that the WDI pin be toggled every second.

If the WDI pin is not toggled within the 1.6 second window

the microprocessor to the initial start-up state. Pulses as

short as 50ns can be applied to the WDI pin. If this feature is

not used, the WDI pin should be open circuited or the logic

placed into a high-impedance state to allow the pin to float.

Backup-Battery Switchover

A power loss can be made less severe if the system RAM

contents are preserved. This is achieved in the ASM690/692/

2

Table 1. Pin Connections in Battery Backup Mode

During the backup power mode, the internal circuitry of the

supervisory circuit draws power from the battery supply.

and the current drawn by the device is typically 35µA. When

switchover comparator, the PFI comparator and WDI

comparator will shut off, reducing the quiescent current drawn

by the IC to less than 1µA.

Condition

SW1/SW2

SW3/SW4

open

closed

open

closed

closed

open

ASM690A/802A/805L Reset Threshold = 4.65V

ASM692A /ASM802M Reset Threshold = 4.4V

Pin

Connection

switch

PFI

Disabled

PFO

Logic-LOW

RESET

Logic-LOW (except on ASM805 where it is

HIGH)

WDI

Watchdog timer disabled

SW1 SW2

D1

D2

SW3 SW4

D3

ASM690A

ASM692A

ASM802L

ASM802M

ASM805L

Figure 3: Internal device configuration of battery

switch-over function