ICL7116 查看數據表（PDF） - Intersil
零件编号
产品描述 (功能)
生产厂家
ICL7116 Datasheet PDF : 14 Pages
| |||
ICL7116, ICL7117
Component Value Selection
Integrating Resistor
Both the buffer amplifier and the integrator have a class A
output stage with 100µA of quiescent current. They can
supply 4µA of drive current with negligible nonlinearity. The
integrating resistor should be large enough to remain in this
very linear region over the input voltage range, but small
enough that undue leakage requirements are not placed on
the PC board. For 2V full scale, 470kΩ is near optimum and
similarly a 47kΩ for a 200mV scale.
Integrating Capacitor
The integrating capacitor should be selected to give the
maximum voltage swing that ensures tolerance buildup will
not saturate the integrator swing (approximately. 0.5V from
either supply). In the ICL7116 or the ICL7117, when the
analog COMMON is used as a reference, a nominal +2V full-
scale integrator swing is fine. For the ICL7117 with +5V
supplies and analog COMMON tied to supply ground, a
±3.5V to +4V swing is nominal. For three readings/second
(48kHz clock) nominal values for ClNT are 0.22µF and 0.1µF,
respectively. Of course, if different oscillator frequencies are
used, these values should be changed in inverse proportion
to maintain the same output swing.
have a full scale reading when the voltage from the
transducer is 0.682V. Instead of dividing the input down to
200mV, the designer should use the input voltage directly
and select VREF = 0.341V. Suitable values for integrating
resistor and capacitor would be 120kΩ and 0.22µF. This
makes the system slightly quieter and also avoids a divider
network on the input. The ICL7117 with ±5V supplies can
accept input signals up to ±4V. Another advantage of this
system occurs when a digital reading of zero is desired for
VIN ≠ 0. Temperature and weighing systems with a variable
fare are examples. This offset reading can be conveniently
generated by connecting the voltage transducer between IN
HI and COMMON and the variable (or fixed) offset voltage
between COMMON and IN LO.
ICL7117 Power Supplies
3. The ICL7117 is designed to work from ±5V supplies.
However, if a negative supply is not available, it can be
generated from the clock output with 2 diodes, 2
capacitors, and an inexpensive lC. Figure 10 shows this
application. See ICL7660 data sheet for an alternative.
V+
An additional requirement of the integrating capacitor is that
it must have a low dielectric absorption to prevent roll-over
errors. While other types of capacitors are adequate for this
application, polypropylene capacitors give undetectable
errors at reasonable cost.
Auto-Zero Capacitor
The size of the auto-zero capacitor has some influence on
the noise of the system. For 200mV full scale where noise is
very important, a 0.47µF capacitor is recommended. On the
2V scale, a 0.047µF capacitor increases the speed of recov-
ery from overload and is adequate for noise on this scale.
V+
OSC 1
OSC 2
OSC 3
ICL7117
GND
V-
CD4009
IN914
+
10
µF
0.047
-
µF
IN914
Reference Capacitor
A 0.1µF capacitor gives good results in most applications.
Generally 1µF will hold the roll-over error to 0.5 counts in this
instance.
Oscillator Components
V- = 3.3V
FIGURE 10. GENERATING NEGATIVE SUPPLY FROM +5V
For all ranges of frequency a 100kΩ resistor is recommended
and the capacitor is selected from the equation:
f = 0--R--.--4-C---5-- For 48kHz Clock (3 Readings/sec), C = 100pF.
Reference Voltage
The analog input required to generate full scale output (2000
counts) is: VlN = 2VREF. Thus, for the 200mV and 2V scale,
VREF should equal 100mV and 1V, respectively. However, in
many applications where the A/D is connected to a
transducer, there will exist a scale factor other than unity
between the input voltage and the digital reading. For
instance, in a weighing system, the designer might like to
In fact, in selected applications no negative supply is
required. The conditions to use a single +5V supply are:
1. The input signal can be referenced to the center of the
common mode range of the converter.
2. The signal is less than ±1.5V.
3. An external reference is used.
10
Share Link: 