Features

ä Power monitoring and switching

for 3-volt battery-backup applica-

tions

ä Write-protect control

ä 2-input decoder for control of up

to 4 banks of SRAM

ä 3-volt primary cell inputs

ä Less than 10ns chip-enable

propagation delay

ä 5% or 10% supply operation

General Description

The CMOS bq2204A SRAM Non-

volatile Controller Unit provides all

necessary functions for converting

up to four banks of standard CMOS

SRAM into nonvolatile read/write

memory.

A precision comparator monitors the 5V

tion. When out-of-tolerance is detected,

the four conditioned chip-enable outputs

are forced inactive to write-protect up to

four banks of SRAM.

During a power failure, the external

supply to one of two 3V backup sup-

plies. On a subsequent power-up, the

SRAMs are write-protected until a

power-valid condition exists.

During power-valid operation, a

two-input decoder transparently se-

lects one of up to four banks of

SRAM.

1

Dec. 1992 B

bq2204A

X4 SRAM Nonvolatile Controller Unit

1

PN220401.eps

16-Pin Narrow DIP or SOIC

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

VCC

BC1

CE

CECON1

CECON2

CECON3

CECON4

NC

VOUT

BC2

NC

A

B

NC

THS

VSS

Pin Names

Supply output

3 volt primary backup cell inputs

THS

Threshold select input

CE

chip-enable active low input

Conditioned chip-enable outputs

A–B

Decoder inputs

NC

No connect

+5 volt supply input

Ground

Up to four banks of CMOS static RAM can be battery-

a power failure, the conditioned chip-enable outputs

ent of the chip-enable input CE.

This activity unconditionally write-protects the external

at 4.62V typical for 5% supply operation.

4.37V typical for 10% supply operation. The THS pin

If a memory access is in process to any of the four external

banks of SRAM during power-fail detection, that memory

cycle continues to completion before the memory is write-

protected. If the memory cycle is not terminated

within

driven high, write-protecting the controlled SRAMs.

Pin Connections

Functional Description