Philips Semiconductors Linear Products
Product specification
ICM7555
General purpose CMOS timer
August 31, 1994
344
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Free-Running Frequency as a Function of RA, RB, and C
Monostable Time Delay vs RA and C
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
CAP
ACIT
ANCE
(
F)
FREQUENCY (Hz)
100.0
10.0
1.0
0.1
0.01
0.001
0.0001
0.0
CAP
ACIT
ANCE
(
F)
TIME DELAY
100ns
1ms
10ms
100ms
1s
10s
1
s
10
s
100
s
VDD = 5V
TA = +25°C
VDD = 5V
TA = +25°C
(RA + 2RB)
1k
10k
100k
1M
10M
1k
10k
100k
1M
10M
RA
Figure 1. Supply Current Transient
Compared With a Standard Bipolar 555
During an Output Transition
500
400
300
200
100
0
200
400
600
800
SUPPL
Y
CURRENT
(mA)
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.