ICM7555, ICM7556
Schematic Diagram
V
DD
P
P
P
P
R
R
R
THRESHOLD
N
N
NPN
CONTROL
VOLTAGE
OUTPUT
P
P
TRIGGER
N
N
N
N
N
N
N
GND
RESET
DISCHARGE
R = 100kΩ ±20% (TYP)
The ICM7555 and ICM7556 produce supply current spikes
of only 2mA - 3mA instead of 300mA - 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.
Application Information
General
The ICM7555 and ICM7556 devices are, in most instances,
direct replacements for the NE/SE 555/6 devices. However,
it is possible to effect economies in the external component
count using the ICM7555 and ICM7556. Because the bipolar
NE/SE 555/6 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 1.
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 2A, 2B, and 3.
500
T
= 25°C
A
400
V
DD
V
300
200
DD
GND
TRIGGER
10K
1
2
3
4
8
7
6
5
SE/NE555
DISCHARGE
THRESHOLD
V
100
0
DD
CONTROL
VOLTAGE
RESET
OPTIONAL
CAPACITOR
ICM7555/56
R
C
0
200
400
600
800
TIME (ns)
FIGURE 2A. ASTABLE OPERATION
FIGURE 1. SUPPLY CURRENT TRANSIENT COMPARED WITH
A STANDARD BIPOLAR 555 DURING AN OUTPUT
TRANSITION
FN2867.9
August 24, 2006
5
INTERSIL [ Intersil ]
