ICM7555_2 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 02 — 3 August 2009 11 of 22
NXP Semiconductors
ICM7555
General purpose CMOS timer
11. Application information
11.1 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 NE/SE555 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 ICM7555 device produces no such transients. See Figure 14.
The ICM7555 produces supply current spikes of only 2 mA to 3 mA instead of
300 mA to 400 mA 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.
11.2 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 Figure 15 and Figure 16 are recommended.
11.3 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 4.5 V or more, the ICM7555
will drive at least 2 standard TTL loads.
T
amb
= +25 °C
(1) NE/SE555
(2) ICM7555
Fig 14. Supply current transient compared with a standard NE/SE555 device during an
output transition
100
300
500
I
DD
(mA)
−100
time (ns)
0 800600200 400
002aae417
(1)
(2)
