FP6809-40CS3P datasheet(8/9 Pages) FITIPOWER

8 / 9 page

FP6809/6810-1.6-JUL-2014

FP6809/6810

fitipower integrated technology lnc.

Application Information (Continued)

Benefits of Highly Accurate Reset Threshold

Most microprocessor supervisor ICs have reset

threshold voltages between 5% and 10% below the

value of nominal supply voltages.

This ensures a

reset will not occur within 5% of the nominal supply,

but will occur when supply is 10% below nominal.

In other words, the reset is guaranteed to assert

after the power supply falls out of regulation, but

keeps inactive even when power is at the minimum

specified operating voltage of the system ICs.

Ensuring a Valid Reset Output Down to VCC=0

When VCC falls below 1V, the FP6809 no longer

sinks

current,

becomes

open

circuit.

Therefore, high-impedance CMOS logic inputs

connected to RESET can drift to undetermined

voltages.

This presents no problem in most

applications

for

microprocessor’s

inoperative

condition

with

VCC below 1V.

However,

applications where RESET must be valid down to

0V, adding a pull-down resistor to RESET causes

stray leakage currents to flow to ground, providing

some impedance between RESET and ground

(Figure 13).

1 is recommended around 100kΩ.

FP6809

µP

RESET

VCC

GND

RESET

INPUT

GND

VCC

100K

Figure 13.

Valid to VCC=0V Circuit

100kΩ

pull-up

resistor

VCC

also

recommended for FP6810 if RESET is required to

remain valid for VCC<1V.

Interfacing to

μPs with Bidirectional Reset Pins

Since the RESET output of FP6809N is open drain,

this device interfaces easily with

μP that has

bidirectional reset pins.

Connect the FP6809N’s

output directly to the microcontroller’s

RESET pin with a single pull-up resistor allows either

device to assert reset (Figure 14).

FP6809-N

µP

RESET

VCC

GND

RESET

INPUT

GND

VCC

Figure14. Interfacing to

μPs with Bidirectional Reset I/O

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