4

FN8226.1

September 18, 2006

Functional Description

The ISL88021 and ISL88022 devices incorporate such features

as Power-On-Reset control, Supply Voltage Supervision,

Undervoltage or Overvoltage Monitoring, and Manual Reset

Assertion.

The ISL88021 and ISL88022 devices provide common preset

optional resistor divider network on V3MON to provide custom

voltage monitoring of voltages greater than 0.6V. An optional

operational functionality with a timing diagram.

Voltage Monitoring

During normal operation, the ISL88021 and ISL88022 monitor

ISL88021 asserts reset if any one of these voltages fall below

their respective voltage trip points and in the case of ISL88022

above the voltage trip point on the V3MON input. The reset

signal effectively prevents the microprocessor from operating

during a power failure, brownout or over voltage condition. This

signal remains active until all monitored voltages meet all

voltage threshold requirements for the reset time delay period

for design flexibility. Figure 1 illustrates the VDD, V2MON and

V3MON input threshold voltages for the various available

options.

Power-On-Reset (POR)

Applying power to the ISL88021 and ISL88022 devices

activates a POR circuit which holds the RESET pin low once

• It prevents the system microprocessor from starting to

operate with insufficient voltage.

• It prevents the processor from operating prior to

stabilization of the oscillator.

• It ensures that the monitored device is held out of operation

until internal registers are properly loaded.

• It allows time for an FPGA to download its configuration prior

to initialization of the circuit.

When all of the monitored voltages meet their respective

input voltage requirements for the specified reset timeout

output low and releases the RST output to allow the system

to begin operation.

On the ISL88021 and ISL88022, users can adjust the

maximum recommended capacitance that should be placed

PCB layout and capacitor placement in order to eliminate

stray capacitance as much as possible, which contributes to

MANUAL RESET

MR Input Voltage Low

0.8

V

MR Input Voltage High

V

MR Minimum Pulse Width

550

ns

Internal Pull-Up Resistor

20

k

Ω

Electrical Specifications

Over the recommended operating conditions unless otherwise specified. (Continued)

SYMBOL

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

FIGURE 1. VDD, V2MON, V3MON VTH vs TEMP

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

4.500

5.000

-40

25

85

TEMPERATURE (°C)

Vth = 4.64V

Vth = 1.69V

Vth = 3.09V

Vth = 2.92V

Vth = 2.32V

Vth = 0.60V

0

2

4

6

8

10

1

5

9 13 17 21 25 29 33 37 41 45

C

ISL88021, ISL88022