ICL7129 Datasheet, PDF (9/11 Pages) Intersil Corporation – 41/2 Digit LCD, Single-Chip A/D Converter

ICL7129
In low resolution applications, where the converter uses only
3¹/₂ digits and 100µV resolution, an R-C type oscillator is ade-
quate. In this application a C of 51pF is recommended and the
resistor value
the converter
isseulescetdedtofriotsmfuf^Oll ^Sp^Cote=nt0ia.4l ^5(4/R1C/₂^.
However,
digits and
when
10µV
resolution) a crystal oscillator is recommended to prevent the
noise from increasing as the input signal is increased due to
frequency jitter of the R-C oscillator. Both R-C and crystal oscil-
lator circuits are shown in Figure 12.
1
40
75kΩ
51pF
ICL7129
2
5pF
V+
1
27kΩ
120kHz
40
10pF
ICL7129
2
CRYSTAL MODE:
PARALLEL
V-
R_S < 50kΩ
C_L < 12pF
C_O < 5pF
FIGURE 12. RC AND CRYSTAL OSCILLATOR CIRCUITS
Powering the ICL7129
The ICL7129 may be operated as a battery powered hand-held
instrument or integrated into larger systems that have more
sophisticated power supplies. Figures 13, 14, and 15 show
various powering modes that may be used with the ICL7129.
The standard supply connection using a 9V battery is shown
in the Typical Application Schematic.
The power connection for systems with +5V and -5V sup-
plies available is shown in Figure 13. Notice that measure-
ments are with respect to ground. COMMON is also tied to
INLO to remove any common-mode voltage swing on the
integrator amplifier inputs.
+5V
0.1µF
24
V+
34
REF HI
35
REF LO
0.1µF
ICL7129
36 _{DGND COM}
28
33
IN HI
0.1µF
32
IN LO
V-
23
ICL8089
V_IN
-5V
FIGURE 13. POWERING THE ICL7129 FROM +5V AND -5V
It is important to notice that in Figure 13, digital ground of the
ICL7129 (DGND pin 36) is not directly connected to power
supply ground. DGND is set internally to approximately 5V
less than the V+ terminal and is not intended to be used as a
power input pin. It may be used as the ground reference for
external logic, as shown in Figure 4 and 5. In Figure 4, DGND
is used as the negative supply rail for external logic provided
that the supply current for the external logic does not cause
excessive loading on DGND. The DGND output can be buff-
ered as shown in Figure 5. Here, the logic supply current is
shunted away from the ICL7129 keeping the load on DGND
low. This treatment of the DGND output is necessary to insure
compatibility when the external logic is used to interface
directly with the logic inputs and outputs of the ICL7129.
When a battery voltage between 3.8V and 6V is desired for
operation, a voltage doubling circuit should be used to bring
the voltage on the ICL7129 up to a level within the power sup-
ply voltage range. This operating mode is shown in Figure 14.
24
V+
REF HI ³⁴
+
3.8V TO
6V
-
REF LO ³⁵
ICL7129
36 _{DGND COM} ²⁸
8
2
+
3
ICL7660 4 10µF
IN HI ³³
IN LO ³²
V-
5
23
+ 10µF
+
V_IN
-
FIGURE 14. POWERING THE ICL7129 FROM A 3.8V TO 6V BATTERY
Again measurements are made with respect to COMMON
since the entire system is floating. Voltage doubling is
accomplished by using an ICL7660 CMOS voltage converter
and two inexpensive electrolytic capacitors. The same princi-
ple applies in Figure 15 where the ICL7129 is being used in
a system with only a single +5V power supply. Here mea-
surements are made with respect to power supply ground.
+5V
24
0.1µF
V+
34
35
0.1µF
36
ICL7129
28
8
2
+
3 _{ICL7660 4 10µF}
5
33
32
V-
23
+ ^10µF
ICL8089
+
V_IN
-
FIGURE 15. POWERING THE ICL7129 FROM A SINGLE
POLARITY POWER SUPPLY
3-39