6

FN8092.3

December 6, 2006

Principles of Operation

The ISL88705 - ISL88813 devices provide those functions

needed for monitoring critical voltages such as power-supply

and battery functions in microprocessor systems. Features of

these supervisors include Power On Reset control, Supply

Voltage Supervision, Power-Fail Detection and Manual Reset

Assertion. The integration of all these features along with high

reset threshold accuracy and low power consumption make

these devices ideal for portable or battery-powered equipment.

Power-On Reset (POR)

Applying power to the device activates a POR circuit which

asserts reset (i.e. RST goes high while RST goes low). These

signals provide several benefits:

• 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.

ensures that the supply voltage has stabilized to sufficient

operating levels.

MANUAL RESET

MR Input Voltage Low

0.8

V

MR Input Voltage High

V

MR Minimum Pulse Width

550

ns

Internal MR Pull-Up Resistor

20

k

Ω

WATCHDOG TIMER (Note 4)

Watchdog Time-out Period

1.0

1.6

2.0

s

WDI Minimum Pulse Width

100

ns

Watchdog Input Voltage Low

V

Watchdog Input Voltage High

V

WDO Output Voltage Low

0.05

0.40

V

0.05

0.40

V

WDO Output Voltage High

V

V

Watchdog Input Current

1µA

POWER-FAIL DETECTION

PFI Input Threshold Voltage

1.20

1.25

1.30

V

20

mV

PFO Output Voltage Low

0.05

0.40

V

0.05

0.40

V

PFO Output Voltage High

V

V

NOTE:

4. Applies to ISL88705, ISL88706, ISL88716, and ISL88813.

Electrical Specifications

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

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

ISL88705, ISL88706, ISL88707, ISL88708, 8SL88716, ISL88813