CDP68HC68A2M Intersil Corporation, CDP68HC68A2M Datasheet - Page 12

• Manufacturer Part Number: CDP68HC68A2M
• Description: CMOS Serial 10-Bit A/D Converter
• Manufacturer: Intersil Corporation

The time constant ( ) for the input network is R
8 is required during the first 1.5 sample clock cycles to
sufficiently encode 10-bit conversion. Therefore, 1.5 T
and T
For example, if R
432kHz, and T
of 32 s. An internal C
The maximum frequency is limited by the device specifica-
tion (see characteristics) and by the (R
tance:
For example, for a 1MHz sample clock R
R
T
f
R
then f
SAMPLE
FIGURE 5B. ANALOG INPUT DURING HOLD AND IDLE TIME
S
EFF
=
S
R
=
FIGURE 5A. ANALOG INPUT DURING SAMPLE TIME
EFF
S
SAMPLE
SIGNAL
SIGNAL
1/f
=
4.688 10
INPUT
INPUT
R
SAMPLE
C
5.33 R
S
NET
+
4.688 10
R
S
NET
=
5.33 R
EFF
8
,
= 2.3 s. This yields a 10-bit conversion time
R
/f
S
S
C
SAMPLE
C.
+
NET
= 1000, f
OSC
8
50
D1
D2
S
+
D1
D2
V
=
85
R
CC
400pF and R
S
V
400pF.
–
68pF, see chart.
CC
+
85 .
85
SAMPLE
400pF
85
R1
.
S
400pF
–
NET
) Series input resis-
S
must be less than
C1
1,
max = 385 .
=
50 .
EFF
OPEN
CIRCUIT
V
V1
2.5V
C
CDP68HC68A2
NET
S
.
8
12
The Internal Schmitt Oscillator
Figure 6 shows a simplified model of the Schmitt oscillator
used to help familiarize the user with its operation. Table 2
shows
capacitance at 5V and 25
When measuring the oscillator, probe capacitance will affect
frequency. An alternative to direct frequency measurement
of the oscillator input is to measure the interval between
successive interrupts in modes 1 and 2.
OSCILLATOR
FIGURE 6. EQUIVALENT CIRCUIT FOR OSCILLATOR INPUT
TABLE 2. TYPICAL OSCILLATOR FREQUENCY vs
INPUT
C(pF)
118
18
38
48
68
EXTERNAL
CAP
330pF
typical
CAPACITANCE AT V
OSC
D1
D2
0.26 - 0.75
0.65 - 2.0
0.54 - 1.6
0.38 - 1.1
internal
1.0 - 3.0
V
V
f(MHz)
DD
SS
o
C.
NMOS
oscillator
PMOS
Q3
Q4
DD
= 5V, T
C(pF)
1018
218
318
409
528
I1
200 A
I2
200 A
frequency
A
= 25
COMPARATOR
HYSTERESIS
o
0.148 - 0.40
0.111 - 0.25
0.107 - 0.23
0.072 - 0.17
0.040 - 0.10
N1
N2
C
f(MHz)
CONTROL
CONTROL
versus