hcf4047 STMicroelectronics, hcf4047 Datasheet - Page 9

• Manufacturer Part Number: hcf4047
• Description: Low Power Monostable/astable Multivibrator
• Manufacturer: STMicroelectronics

6 - POWER CONSUMPTION
In the standby mode (Monostable or Astable),
power dissipation will be a function of leakage
current in the circuit, as shown in the static
electrical characteristics. For dynamic operation,
the power needed to charge the external timing
capacitor C is given by the following formula :
Astable Mode :
P = 2CV
P = 4CV
Monostable Mode : P = ——————————
(Output at Pin 10 and 11)
The circuit is designed so that most of the total
power is consumed in the external components. In
practice, the lower the values of frequency and
voltage used, the closer the actual power
dissipation will be to the calculated value.
Because the power dissipation does not depend
on R, a design for minimum power dissipation
would be a small value of C. The value of R would
depend on the desired period (within the
limitations discussed above).
7 - TIMING-COMPONENT LIMITATIONS
TEST CIRCUIT
C
R
R
L
L
T
= 50pF or equivalent (includes jig and probe capacitance)
= 200K
= Z
OUT
of pulse generator (typically 50 )
2
2
f. (Output at Pin 13)
f. (Output at Pin 10 and 11)
(2.9CV
2
) (Duty Cycle)
T
The capacitor used in the circuit should be
non-polarized and have low leakage (i.e. the
parallel resistance of the capacitor should be an
order of magnitude greater than the external
resistor used). Three is no upper or lower limit for
either R or C value to maintain oscillation.
However, in consideration of accuracy, C must be
much larger than the inherent stray capacitance in
the system (unless this capacitance can be
measured and taken into account). R must be
much larger than the COS/MOS "ON" resistance
in series with it, which typically is hundreds of
ohms. In addition, with very large values of R,
some short-term instability with respect to time
may be noted.
The recommended values for these components
to maintain agreement with previously calculated
formulas without trimming should be :
C > 100pF, up to any practical value, for astable
modes ;
C > 1000pF, up to any practical value, for
monostable modes.
10K < R < 1M .
HCF4047B
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