Philips Semiconductors Linear Products

Product specification

ICM7555

General purpose CMOS timer

August 31, 1994

344

TYPICAL PERFORMANCE CHARACTERISTICS (continued)

100.0

10.0

1.0

0.1

0.01

0.001

0.0001

0.0

0.1

1.0

10

100

1k

10k

100k

1M

10M

FREQUENCY (Hz)

100.0

10.0

1.0

0.1

0.01

0.001

0.0001

0.0

TIME DELAY

100ns

1ms

10ms

100ms

1s

10s

1

µs

10

µs

100

µs

VDD = 5V

TA = +25°C

VDD = 5V

TA = +25°C

(RA + 2RB)

1k

Ω

10k

Ω

100k

Ω

1M

Ω

10M

Ω

1k

Ω

10k

Ω

100k

Ω

1M

Ω

10M

Ω

RA

Figure 1. Supply Current Transient

Compared With a Standard Bipolar 555

During an Output Transition

500

400

300

200

100

0

0

200

400

600

800

TIME (ns)

TA = +25°C

NE/SE555

ICM7555

APPLICATION NOTES

General

The ICM7555 device is, in most instances, a direct replacement for

the NE/SE555 device. However, it is possible to effect economies in

the external component count using the ICM7555. Because the

bipolar 555 device produces large crowbar currents in the output

driver, it is necessary to decouple the power supply lines with a

good capacitor close to the device. The 7555 device produces no

such transients. See Figure 1.

The ICM7555 produces supply current spikes of only 2-3mA instead

of 300-400mA and supply decoupling is normally not necessary.

Secondly, in most instances, the CONTROL VOLTAGE decoupling

capacitors are not required since the input impedance of the CMOS

comparators on chip are very high. Thus, for many applications, 2

capacitors can be saved using an ICM7555.

Power Supply Considerations

Although the supply current consumed by the ICM7555 device is

very low, the total system supply can be high unless the timing

components are high impedance. Therefore, high values for R and

low values for C in Figures 2 and 3 are recommended.

Output Drive Capability

The output driver consists of a CMOS inverter capable of driving

most logic families including CMOS and TTL. As such, if driving

CMOS, the output swing at all supply voltages will equal the supply

voltage. At a supply voltage of 4.5V or more, the ICM7555 will drive

at least 2 standard TTL loads.