CAT25C021P-28TE13 View Datasheet(PDF) - Catalyst Semiconductor => Onsemi

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CAT25C021P-28TE13

Supervisory circuits with SPI serial E2EPROM, precision reset controller and watchdog timer

Catalyst Semiconductor => Onsemi 

CAT25CXXX

Advanced

DEVICE OPERATION FOR THE

SUPERVISORY CIRCUIT

Reset Controller Description

The CAT25CXXX provides a precision RESET control-

ler that ensures correct system operation during brown-

out and power-up/down conditions. It is configured

with open drain RESET outputs. During power-up, the

RESET outputs remain active until VCC reaches the

VTH threshold and will continue driving the outputs for

approximately 200ms (tPURST) after reaching VTH. After

the tPURST timeout interval, the device will cease to drive

reset outputs. At this point the reset outputs will be

pulled up or down by their respective pull up/pull down

devices. During power-down, the RESET outputs will

begin driving active when VCC falls below VTH. The

RESET outputs will be valid so long as VCC is >1.0V

(VRVALID).

The RESET pins are I/Os; therefore, the CAT25CXXX

can act as a signal conditioning circuit for an externally

applied reset. The inputs are level triggered; that is, the

RESET input in the 25CXXX will initiate a reset timeout

after detecting a high and the RESET input in the

25CXXX will initiate a reset timeout after detecting a low.

Watchdog Timer

The Watchdog Timer provides an independent protec-

tion for microcontrollers. During a system failure, the

CAT25CXXX will respond with a reset signal after a

time out period (the time out period is defined by the

watchdog timer bits WD0 an d WD1) for lack of activity.

25CXXX is designed with the Watchdog Timer feature

on the CS input. For the 25CXXX, if the microcontroller

does not toggle the CS pin within the time out period the

Watchdog Timer times out. This will generate a reset

condition on reset outputs. The Watchdog Timer is

cleared by any transition on CS.

As long as the reset signal is asserted, the Watchdog

Timer will not count and will stay cleared.

Reset Threshold Voltage

From the factory the 25CXXX is offered in six different

variations of reset threshold voltages. They are 4.50-

4.75V, 4.25-4.50V, 3.00-3.15V, 2.85-3.00V, 2.55-2.70V

and 1.7-1.8V. To provide added flexibility to design

engineers using this product, the 25CXXX is designed

with an additional feature of programming the reset

threshold voltage. This allows the user to change the

existing reset threshold voltage to one of the other five

reset threshold voltages. Once the reset threshold

voltage is selected it will not change even after cycling

the power, unless the user uses the programmer to

change the reset threshold voltage. However, the

programming function is available only through third

party programmer manufacturers. Please call Catalyst

for a list of programmer manufacturers who support this

function.

Figure 8. Page Write Instruction Timing

012345678

21 22 23 24-31 32-39

SK

CS

SI

00 00 00 10

SO

ADDRESS

Data Data Data

Byte 1 Byte 2 Byte 3

Data

Byte N

Stock No. 21085-01 4/98

9-104

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