ICL8052 Datasheet, PDF (13/21 Pages) Intersil Corporation – 14-Bit/16-Bit, Microprocessor- Compatible, 2-Chip, A/D Converter

ICL8052/ICL7104, ICL8068/ICL7104
TABLE 3. THREE-STATE BYTE FORMATS AND ENABLE PINS
CE/LD
HBEN
MBEN
LBEN
ICL7104-16 POL O/R B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1
HBEN
LBEN
ICL7104-14
POL O/R B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1
TABLE 4. TYPICAL COMPONENT VALUES (V++ = +15V, V+ = 5V, V- = 5V, V- = -15V, f_CLOCK = 200kHz)
ICL8052/8068 WITH
ICL7104-16
ICL7104-14
Full scale V_IN
Buffer Gain
200
800
4000
100
4000
10
1
1
10
1
R_INT
C_INT
C_AZ
C_REF
V_REF
Resolution
100
43
200
47
180
0.33
0.33
0.33
0.1
0.1
1
1
1
1
1
10
1
1
10
1
100
400
2000
50
2000
3.1
12
61
6.1
244
UNIT
mV
V/V
kΩ
µF
µF
µF
mV
µV
10-50K
+15V -15V ^100kΩ
R_INT
C_INT
REF
OUT
300pF
5kΩ
10kΩ
-BUF IN BUF OUT -INT IN INT OUT
8 7 1 10
9
6
BUFFER
INT.
3 _REF.
-
11
INTEG.
-
14
COMP.
A1
A2
-
+
+
8068
A3
+
2
5 +BUF IN 13
+INT IN 12
-1.2V
COMP
OUT
+5V
-15V
TO ICL7104
FIGURE 7. ADDING BUFFER GAIN TO ICL8068
Buffer Gain
At the end of the auto-zero interval, the instantaneous noise
voltage on the auto-zero capacitor is stored, and subtracts
from the input voltage while adding to the reference voltage
during the next cycle. The result is that this noise voltage
effectively is somewhat greater than the input noise voltage
of the buffer itself during integration. By introducing some
voltage gain into the buffer, the effect of the auto-zero noise
(referred to the input) can be reduced to the level of the
inherent buffer noise. This generally occurs with a buffer gain
of between 3 and 10. Further increase in buffer gain merely
increases the total offset to be handled by the auto-zero
loop, and reduces the available buffer and integrator swings,
without improving the noise performance of the system. The
circuit recommended for doing this with the
ICL8068/ICL7104 is shown in Figure 7. With careful layout,
the circuit shown can achieve effective input noise voltages
on the order of 1 to 2µV, allowing full 16-bit use with full scale
inputs of a low as 150mV. Note that at this level, thermoelec-
tric EMFs between PC boards, IC pins, etc., due to local
temperature changes can be very troublesome. For further
discussion, see Application Note AN030.
ICL8052 vs ICL8068
The ICL8052 offers significantly lower input leakage currents
than the ICL8068, and may be found preferable in systems
with high input impedances. However, the ICL8068 has
substantially lower noise voltage, and for systems where
system noise is a limiting factor, particularly in low signal
level conditions, will give better performance.
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