Alliance Semiconductor ASM690A, ASM692A, ASM802L, ASM802M, ASM805L Service Manual

查询ASM690A供应商

October 2003

ASM690A / 692A
ASM802L / 802M

ASM805L

rev 1.0

µP Power Supply Supervisor With Battery Backup Switch

General Description

The AS690A / AS692A / AS802L / AS802M / AS805L offers

complete single chip solutions for power supply monitoring and

control battery functions in microprocessor systems. Each

device implements four functions: Reset control, watchdog

monitoring, battery-backup switching and power-failure

monitoring. In addition to microprocessor reset under power-up

and power-down conditions, these devices provide battery-

backup switching to maintain control in power loss and brown-

out situations. Additional monitoring capabilities can provide an

early warning of unregulated power supply loss before the

voltage regulator drops out. The important features of these

four functions are:

• 1.6 second watchdog timer to keep microprocessor
responsive

• 4.40V or 4.65V V

threshold for microprocessor reset at

CC

power-up and power-down

• SPDT (Single-pole, Double-throw) PMOS switch connects
backup power to RAM if V

CC

fails

• 1.25V threshold detector for power loss or general purpose
voltage monitoring

These features are pin-compatible with the industry standard

power-supply supervisors. Short-circuit and thermal protection

have also been added. The AS690A / AS802L / AS805L

generate a reset pulse when the supply voltage drops below

4.65V and the AS692A / AS802M generate a reset below

4.40V. The ASM802L / ASM802M have power-fail accuracy to

± 2%. The ASM805L is the same as the ASM690A except that

RESET is provided instead of RESET

.

Features

• Two precision supply-voltage monitor options

•4.65V (AS690A / AS802L / AS805L)

•4.40V (AS692A / AS802M )

• Battery-backup power switch on-chip

• Watchdog timer: 1.6 second timeout

• Power failure / low battery detection

• Short circuit protection and thermal limiting

• Small 8-pin SO package

• No external components

• Specified over full temperature range

Applications

• Embedded control systems

• Portable/Battery operated systems

• Intelligent instruments

• Wireless instruments

• Wireless communication systems

• PDAs and hand-held equipments

• µP / µC power supply monitoring

• Safety system

Typical Operating Circuit

Unregulated DC

R

R

0.1 µF

1

2

+

3.6 V

_

Lithium

Battery

PFI

V

BATT

GND

ASM690A

Regulated +5V

V

CC

RESET

PFO

WDI

V

OUT

Block Diagram

8

V

V

BATT

BATT

V

V

WDI

WDI

PFI

PFI

8

2

2

CC

CC

6

6

4

4

ASM690A, ASM692A, ASM802L, ASM802M, (ASM805L)

Battery-Switchover Circuit

Battery-Switchover Circuit

+

+

|+

|+

-

-

1.25V

1.25V

3.5V

3.5V

+

+

|+

|+

-

-

-

-

|+

|+

+

+

0.8V

0.8V

3

GND

Reset

Reset

Generator

Generator

Watchdog

Watchdog

Timer

Timer

1.25V

1.25V

|+

|+

RESET

NMI

I/O LINE

GND

V

CC

GND

-

-

+

+

V

CC

CMOS

RAM

1

1

7

7

5

5

BUS

V

V

OUT

OUT

RESET

RESET

(RESET)

(RESET)

PFO

PFO

Alliance Semiconductor

2575 Augustine Drive . Santa Clara, CA 95054 . Tel: [phone] . Fax: [phone] . www.alsc.com

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

ASM690A / 692A
ASM802L / 802M

October 2003

rev 1.0

Pin Configuration

Pin Description

Pin Number

ASM690A /

ASM692A

ASM802L /

ASM802M

11

ASM805L

Plastic/CerDip/SO

V

OUT

V

CC

GND

PFI

Name Function

Voltage supply for RAM. When VCC is above the reset threshold, V

V

OUT

V

output will be connected to the backup supply at V

higher) through the MOS switch to provide continuous power to the CMOS RAM.

ASM690A

1

ASM692A

2

ASM802L

3

ASM802M

4

(ASM805L)

through a P-Channel MOS device. If VCC falls below the reset threshold, this

CC

V

8

BATT

7

RESET (RESET)

6

WDI

PFO

5

ASM805L

OUT

(or VCC, whichever is

BATT

connects to

22

3 3 GND Ground

44PFI

55PFO

66WDI

7 - RESET

- 7 RESET Active-HIGH reset output. The inverse of RESET

88

V

CC

V

BATT

+5V power supply input.

Power failure monitor input. PFI is connected to the internal power fail comparator
which is referenced to 1.25V. The power fail output (PFO
remains HIGH if PFI is above 1.25V. If this feature is unused, the PFI pin should be
connected to GND or V

Power-fail output. PFO is active LOW whenever the PFI pin is less than 1.25V.

Watchdog input. The WDI input monitors microprocessor activity. An internal timer
is reset with each transition of the WDI input. If the WDI is held HIGH or LOW for
longer than the watchdog timeout period, typically 1.6 seconds, RESET (or RESET
is asserted for the reset pulse width time, t

Active-LOW reset output. When triggered by VCC falling below the reset threshold

or by watchdog timer timeout, RESET (or RESET
width t

(4.65V in ASM690A / ASM802L and 4.4V in the ASM692A / ASM802L) and
remains low for 200ms after V

Auxiliary power or backup-battery input. V

function is not used. The input has about 40mV of hysteresis to prevent rapid tog­gling between V

, typically 200ms. It will remain low if VCC is below the reset threshold

RS

and V

CC

OUT

.

, of 140ms, minimum.

RS

rises above the reset threshold.

CC

should be connected to GND if the

BATT

.

BATT

) is active LOW but

)

) pulses low for the reset pulse

.

µP Power Supply Supervisor With Battery Backup Switch

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

2 of 13

ASM690A / 692A
ASM802L / 802M

October 2003

rev 1.0

Detailed Description

It is important to initialize a microprocessor to a known state

in response to specific events that could create code

execution errors and “lock-up”. The reset output of these

supervisory circuits send a reset pulse to the microprocessor

in response to power-up, power-down/power-loss or a

watchdog time-out.

RESET/RESET

Power-up reset occurs when a rising V

threshold, V

output is asserted in the appropriate logic state for the

duration of t

200ms and is LOW for the ASM690A, ASM692A, ASM802

and HIGH for the ASM805L. Figure 1 shows the reset pin

timing.

Timing

reaches the reset

CC

, forcing a reset condition in which the reset

RT

. The reset pulse width, tRS, is typically around

RS

ASM805L

Application Information

Microprocessor Interface

The ASM690 has logic-LOW RESET output while the

ASM805 has an inverted logic-HIGH RESET output.

Microprocessors with bidirectional reset pins can pose a

problem when the supervisory circuit and the microprocessor

output pins attempt to go to opposite logic states. The
problem can be resolved by placing a 4.7kΩ resistor between

the RESET output and the microprocessor reset pin. This is

shown in Figure 2. Since the series resistor limits drive

capabilities, the reset signal to other devices should be

buffered.

Power-loss or “brown-out” reset occurs when V

the reset threshold resulting in a reset assertion for the

duration of t

V

is between VRT and 1.1V, the lowest VCC for which these

CC

devices can provide a guaranteed logic-low output. To ensure

logic inputs connected to the ASM690A / ASM692A/ASM802

RESET pin are in a known state when V
100kΩ pull-down resistor at RESET is needed: the logic-high

ASM805L will need a pull-up resistor to V

Watchdog Timer

A Watchdog time-out reset occurs when a logic “1” or logic

“0” is continuously applied to the WDI pin for more than 1.6

seconds. After the duration of the reset interval, the watchdog

timer starts a new 1.6 second timing interval; the

microprocessor must service the watchdog input by changing

states or by floating the WDI pin before this interval is

finished. If the WDI pin is held either HIGH or LOW, a reset

pulse will be triggered every 1.8 seconds (the 1.6 second

timing interval plus the reset pulse width t

RS. The reset signal remains asserted as long as

CC

CC

RS

dips below

CC

is under 1.1V, a

.

).

Figure 1: RESET/RESET Timing

V

CC

Power Supply

RESET

ASM690A

GND

Bi-directional I/O pin

4.7K

BUF

V

CC

Ω

RESET

GND

Buffered

RESET

Figure 2: Interfacing with bi-directional

microprocessor reset inputs

µP Power Supply Supervisor With Battery Backup Switch

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

3 of 13

ASM690A / 692A
ASM802L / 802M

October 2003

rev 1.0

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

(minimum t

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/

802/805 by switching from the failed V

power source connected at V

reset threshold voltage (V

V

. The V

BATT

2Ω PMOS switch but a brown-out or loss of VCC will cause a

switchover to V

Although both conditions (VCC < VRT and VCC <V

occur for the switchover to V

switched back to V

the voltage at V

device diode (D1 in Figure 3) will be forward biased if V

exceeds VCC by more than a diode drop when VCC is

switched to V

V

be no greater than VRT +0.6V.

BATT

+ tRS), a reset pulse will be asserted to return

WD

to an alternate

CC

when VCC is less than the

BATT

< VRT), and VCC is less than

CC

pin is normally connected to VCC through a

OUT

by means of a 20Ω PMOS switch.

BATT

BATT

to occur, V

BATT

when VCC exceeds VRT irrespective of

CC

. It should be noted that an internal

BATT

. Because of this it is recommended that

OUT

OUT

will be

) must

BATT

ASM805L

V

BATT

D2

SW2

SW1

ASM690A
ASM692A

ASM802L

ASM802M

Figure 3: Internal device configuration of battery

switch-over function

Table 1. Pin Connections in Battery Backup Mode

Pin Connection

V

OUT

V

BATT

PFI Disabled

PFO Logic-LOW

RESET

Connected to V

switch

Connected to V

Logic-LOW (except on ASM805 where it is
HIGH)

D1

ASM805L

D3

V

OUT

through internal PMOS

BATT

OUT

V

SW3

CC

SW4

Condition SW1/SW2 SW3/SW4

V

> Reset Threshold

CC

V

< Reset Threshold

CC

V

> V

CC

BATT

< Reset Threshold

V

CC

V

< V

CC

BATT

ASM690A/802A/805L Reset Threshold = 4.65V
ASM692A /ASM802M Reset Threshold = 4.4V

open closed

open closed

closed open

µP Power Supply Supervisor With Battery Backup Switch

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

WDI Watchdog timer disabled

During the backup power mode, the internal circuitry of the

supervisory circuit draws power from the battery supply.

While V

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

V

CC

switchover comparator, the PFI comparator and WDI

comparator will shut off, reducing the quiescent current drawn

by the IC to less than 1µA.

is still alive, the comparator circuits remain alive

CC

drops more than 1.1V below V

BATT

, the internal

4 of 13