ICM7242CBA INTERSIL [Intersil Corporation], ICM7242CBA Datasheet - Page 3

• Manufacturer Part Number: ICM7242CBA
• Description: Long Range Fixed Timer
• Manufacturer: INTERSIL [Intersil Corporation]

Test Circuit
NOTE:
4.
Application Information
Operating Considerations
Shorting the RC terminal or output terminals to V
exceed dissipation ratings and/or maximum DC current limits
(especially at high supply voltages).
There is a limitation of 50pF maximum loading on the TB I/O
terminal if the timebase is being used to drive the counter
section. If higher value loading is used, the counter sections
may miscount.
For greatest accuracy, use timing component values shown
in Figure 8. For highest frequency operation it will be desir-
able to use very low values for the capacitor; accuracy will
decrease for oscillator frequencies in excess of 200kHz.
The timing capacitor should be connected between the RC
pin and the positive supply rail, V
When system power is turned off, any charge remaining on
the capacitor will be discharged to ground through a large
internal diode between the RC node and V
ence the timing capacitor to ground, since there is no high
current path in this direction to safely discharge the capacitor
when power is turned off. The discharge current from such a
configuration could potentially damage the device.
When driving the counter section from an external clock, the
optimum drive waveform is a square wave with an amplitude
equal to the supply voltage. If the clock is a very slow ramp
triangular, sine wave, etc., it will be necessary to “square up”
the waveform; this can be done by using two CMOS invert-
ers in series, operating from the same supply voltage as the
ICM7242.
The ICM7242 is a non-programmable timer whose principal
applications will be very low frequency oscillators and long
range timers; it makes a much better low frequency oscilla-
tor/timer than a 555 or ICM7555, because of the on-chip
8-bit counter. Also, devices can be cascaded to produce
extremely low frequency signals.
Because outputs will not be ANDed, output inverters are
used instead of open drain N-Channel transistors, and the
external resistors used for the 2242 will not be required for
the ICM7242. The ICM7242 will, however, plug into a socket
for the 2242 having these resistors.
2
1
and 2
8
outputs are inverters and have active pullups.
2
8
2
(RC/256) OUTPUT
1
(RC/2) OUTPUT
V
DD
DD
, as shown in Figure 1.
1
2
3
4
SS
. Do NOT refer-
DD
ICM7242
may
RESET
8
7
6
5
8-165
The timing diagram for the ICM7242 is shown in Figure 1.
Assuming that the device is in the RESET mode, which
occurs on power up or after a positive signal on the RESET
terminal (if TRIGGER is low), a positive edge on the trigger
input signal will initiate normal operation. The discharge
transistor turns on, discharging the timing capacitor C, and
all the flip-flops in the counter chain change states. Thus, the
outputs on terminals 2 and 3 change from high to low states.
After 128 negative timebase edges, the 2
the high state.
TIME BASE INPUT/OUTPUT
OUTPUTS
FIGURE 1. TIMING DIAGRAMS OF OUTPUT WAVEFORMS
FIGURE 2. USING THE ICM7242 AS A RIPPLE COUNTER
TRIGGER
128RC
128RC
C
R
V
f
f
FOR THE ICM7242 (COMPARE WITH FIGURE 5)
(DIVIDER)
DD
IN/2
IN/256
TIME BASE PERIOD = 1.0RC;
1s = 1M x 1 F
1
2
3
4
V
DD
128RC
8
7
6
5
V
f
IN
DD
TRIGGER INPUT
(TERMINAL 6)
TIMEBASE INPUT
(TERMINAL 8)
(TERMINAL 2)
(TERMINAL 3) (ASTABLE
OR “FREE RUN” MODE)
(TERMINAL 3)
(MONOSTABLE
OR “ONE SHOT” MODE)
2 OUTPUT
128/256 OUTPUT
128/256 OUTPUT
8
output returns to
3
1
/
/
4
4
(V+)
(V+)