X5328PIZ datasheet(5/21 Pages) INTERSIL

5 / 21 page

FN8132.1

October 17, 2005

PRINCIPLES OF OPERATION

Power-On Reset

Application of power to the X5328/X5329 activates a

Power-on Reset Circuit. This circuit goes active at

about 1V and pulls the RESET/RESET pin active. This

signal prevents the system microprocessor from start-

ing to operate with insufficient voltage or prior to stabi-

lization of the oscillator. When VCC exceeds the device

VTRIP value for 200ms (nominal) the circuit releases

RESET/RESET, allowing the processor to begin exe-

cuting code.

Low Voltage Monitoring

During operation, the X5328/X5329 monitors the VCC

level and asserts RESET/RESET if supply voltage

falls

below

preset

minimum

VTRIP.

The

RESET/RESET signal prevents the microprocessor

from operating in a power fail or brownout condition.

The RESET/RESET signal remains active until the

voltage drops below 1V. It also remains active until

VCC returns and exceeds VTRIP for 200ms.

VCC Threshold Reset Procedure

The X5328/X5329 has a standard VCC threshold

(VTRIP) voltage. This value will not change over normal

operating and storage conditions. However, in applica-

tions where the standard VTRIP is not exactly right, or

for

higher

precision

the

VTRIP value, the

X5328/X5329 threshold may be adjusted.

Setting the VTRIP Voltage

This procedure sets the VTRIP to a higher voltage

value. For example, if the current VTRIP is 4.4V and

the new VTRIP is 4.6V, this procedure directly makes

the change. If the new setting is lower than the current

setting, then it is necessary to reset the trip point

before setting the new value.

To set the new VTRIP voltage, apply the desired VTRIP

threshold to the VCC pin and tie the CS pin and the WP

pin HIGH. RESET/RESET and SO pins are left uncon-

nected. Then apply the programming voltage VP to

both SCK and SI and pulse CS LOW then HIGH.

Remove VP and the sequence is complete.

Figure 1. Set VTRIP Voltage

Resetting the VTRIP Voltage

This procedure sets the VTRIP to a “native” voltage

level. For example, if the current VTRIP is 4.4V and the

VTRIP is reset, the new VTRIP is something less than

1.7V. This procedure must be used to set the voltage

to a lower value.

To reset the VTRIP voltage, apply a voltage between

2.7 and 5.5V to the VCC pin. Tie the CS pin, the WP

pin, and the SCK pin HIGH. RESET/RESET and SO

pins are left unconnected. Then apply the program-

ming voltage VP to the SI pin ONLY and pulse CS

LOW then HIGH. Remove VP and the sequence is

complete.

Figure 2. Reset VTRIP Voltage

SCK

VCC

X5328, X5329

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