Datasheet

December 1990 11
Philips Semiconductors Product specification
14-stage binary ripple counter with oscillator 74HC/HCT4060
Fig.7 Test set-up for measuring forward
transconductance g
fs
=di
o
/ dv
i
at v
o
is
constant (see also graph Fig.8);
MR = LOW.
handbook, halfpage
MBA333
14
12
10
8
6
4
2
0123456
g
fs
(mA/V)
CC
V
(V)
max.
min.
typ.
Fig.8 Typical forward transconductance g
fs
as a
function of the supply voltage V
CC
at
T
amb
=25°C.
Fig.9 RC oscillator frequency as a function of
R
t
and C
t
at V
CC
= 2.0 to 6.0 V; T
amb
=25°C.
C
t
curve at R
t
= 100 kΩ; R2 = 200 kΩ.
R
t
curve at C
t
= 1 nF; R2 = 2 × R
t
.
RC OSCILLATOR
Fig.10 Example of a RC oscillator.
Typical formula for oscillator frequency:
f
osc
1
2.5 R
t
C
t
××
--------------------------------
=
TIMING COMPONENT LIMITATIONS
The oscillator frequency is mainly determined by R
t
C
t
, provided R2 ≈ 2R
t
and R2C2 << R
t
C
t
. The function of R2 is to
minimize the influence of the forward voltage across the input protection diodes on the frequency. The stray capacitance
C2 should be kept as small as possible. In consideration of accuracy, C
t
must be larger than the inherent stray
capacitance. R
t
must be larger than the “ON” resistance in series with it, which typically is 280 Ω at V
CC
= 2.0 V, 130 Ω at
V
CC
= 4.5 V and 100 Ω at V
CC
= 6.0 V.
The recommended values for these components to maintain agreement with the typical oscillation formula are:
C
t
> 50 pF, up to any practical value,
10 kΩ<R
t
<1 MΩ.
In order to avoid start-up problems, R
t
≥ 1 kΩ.