Data Sheet

ICM7555, ICM7556
FN2867 Rev 1.00 Page 5 of 13
June 28, 2016
Application Information
General
The ICM7555 and ICM7556 devices are, in most instances,
direct replacements for the SE/NE 555/556 devices. However,
it is possible to effect economies in the external component
count using the ICM7555 and ICM7556. Because the bipolar
SE/NE 555/556 devices produce 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
and ICM7556 devices produce no such transients (see
Figure 3
).
The ICM7555 and ICM7556 produce supply current spikes of
only 2mA to 3mA instead of 300mA to 400mA and supply
decoupling is normally not necessary. Also, 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, two capacitors can
be saved using an ICM7555 and three capacitors with an
ICM7556.
POWER SUPPLY CONSIDERATIONS
Although the supply current consumed by the ICM7555 and
ICM7556 devices is very low, the total system supply current
can be high unless the timing components are high
impedance. Therefore, use high values for R and low values for
C in Figures 4
, 5, and 6.
Schematic Diagram
FIGURE 2. SCHEMATIC DIAGRAM
RESET DISCHARGE
TRIGGER
THRESHOLD
GND
OUTPUT
CONTROL
VOLTAGE
R
NN
NPN
P
R
R
V
DD
NNNNN
PP
NN
PP P
R = 100kΩ ±20% (TYP)
TIME (ns)
400 8006002000
0
100
200
300
400
500
SUPPLY CURRENT (mA)
SE/NE 555
T
A
= +25°C
ICM7555/556
FIGURE 3. SUPPLY CURRENT TRANSIENT COMPARED WITH A
STANDARD BIPOLAR 555 DURING AN OUTPUT
TRANSITION
GND
TRIGGER
OUTPUT
RESET
1
2
3
4
8
7
6
5
V
DD
DISCHARGE
THRESHOLD
CONTROL
VOLTAGE
V
DD
10k
ALTERNATE OUTPUT
OPTIONAL
CAPACITOR
C
V
DD
R
FIGURE 4. ASTABLE OPERATION