ICM7555_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 3 August 2009

13 of 22

NXP Semiconductors

ICM7555

General purpose CMOS timer

11.6 Control voltage

The CONTROL_VOLTAGE terminal permits the two trip voltages for the THRESHOLD

and TRIGGER internal comparators to be controlled. This provides the possibility of

oscillation frequency modulation in the astable mode, or even inhibition of oscillation,

depending on the applied voltage. In the monostable mode, delay times can be changed

by varying the applied voltage to the CONTROL_VOLTAGE pin.

11.7 RESET

The RESET terminal is designed to have essentially the same trip voltage as the standard

NE/SE555 device, i.e., 0.6 V to 0.7 V. At all supply voltages it represents an extremely

high input impedance. The mode of operation of the RESET function is, however, much

improved over the standard NE/SE555 device in that it controls only the internal flip-flop,

which in turn controls simultaneously the state of the OUTPUT and DISCHARGE pins.

This avoids the multiple threshold problems sometimes encountered with slow falling

edges in the NE/SE555 devices.

Fig 16. Monostable operation

GND

TRIGGER

OUTPUT

RESET

1

2

3

4

DISCHARGE

THRESHOLD

CONTROL_VOLTAGE

8

7

6

5

002aae419

RA

optional

capacitor

C