ICL761X_1 Datasheet, PDF (21/26 Pages) Maxim Integrated Products – Single/Dual/Triple/Quad Operational Amplifiers

Single/Dual/Triple/Quad
Operational Amplifiers
Detailed Description
Quiescent Current Selection
The voltage input to the I_Q pin of the single and triple
amplifiers selects a quiescent current (I_Q) of 10µA,
100µA, or 1000µA. The dual and quad amplifiers have
fixed quiescent current (I_Q) settings. Unity-gain band-
width and slew-rate increase with increasing quiescent
current, as does output sink current capability. The out-
put source current capability is independent of quies-
cent current.
The lowest I_Q setting that results in sufficient bandwidth
and slew rate should be selected for each specific
application.
The I_Q pin of the single and triple amplifiers controls
the quiescent current as follows:
I_Q = 10µA
I_Q = 100µA
I_Q = 1mA
I_Q pin to V+
I_Q pin between V- + 0.8V and V+ - 0.8V
I_Q pin to V-
Input Offset Nulling
The input offset can be nulled by connecting a 25kΩ
pot between the OFFSET terminals with the wiper con-
nected to V+. At quiescent currents of 1mA and 100µA,
the nulling range provided is adequate for all V_OS
selections. However, with higher values of V_OS, and an
I_Q of 10µA, nulling may not be possible.
Frequency Compensation
All of the ICL7611 and ICL7621 series except the
ICL7614 are internally compensated for unity-gain
operation. The ICL7614 is externally compensated by a
capacitor connected between COMP and OUT pins,
with 39pF being greater than unity. The compensation
capacitor value may be reduced to increase the band-
width and slew rate. The ICL7132 is not compensated
and does not have frequency compensation pins. Use
only at gains 20 at I_Q of 1mA; at gains > 10 at I_Q of
100µA; at gain > 5 at I_Q of 10µA.
Output Loading Considerations
Approximately 70% of the amplifier’s quiescent current
flows in the output stage. The output swing can
approach the supply rails for output loads of 1MΩ,
100kΩ, and 10kΩ, using the output stage in a highly
linear Class A mode. Crossover distortion is avoided
and the voltage gain is maximized in this mode. The
output stage, however, can also be operated in Class
AB, which supplies higher output currents (see the
Typical Operating Characteristics). The voltage gain
decreases and the output transfer characteristic is non-
linear during the transition from Class A to Class B
operation.
The output stage, with a gain that is directly proportion-
al to load impedance, approximates a transconduc-
tance amplifier. Approximately the same open-loop
gains are obtained at each of the I_Q settings if corre-
sponding loads of 10kΩ, 100kΩ, and 1MΩ are used.
The maximum output source current is higher than the
maximum sink current, and is independent of I_Q.
Like most amplifiers, there are output loads for which
the amplifier stability is not guaranteed. In particular,
avoid capacitive loads greater than 100pF; and while
on the 1mA I_Q setting, avoid loads less than 5kΩ. Since
the output stage is a transconductance output, very
large (>10µF) capacitive loads will create a dominant
pole and the output will be stable, even with loads that
are less than 5kΩ.
Extended Common-Mode Voltage Range
(ICL7612/ICL7616)
A common-mode voltage range that includes both V+
and V- is often desirable, especially in single-supply
operation. The ICL7612/ICL7616 extended common-
mode range op amps are designed specifically to meet
this need. The ICL7612 input common-mode voltage
range (CMVR) extends beyond both power-supply rails
when operated with at least 3V total supply and an I_Q
of 10µA or 100µA. The ICL7616 CMVR includes the
negative supply voltage (or ground when operated with
a single supply) at an I_Q or 10µA or 100µA.
PC Board Layout
Careful PC board layout techniques must be used to
take full advantage of the very low bias current of the
ICL7611 family. The inputs should be encircled with a
low-impedance trace, or guard, that is at the same
potential as the inputs. In an inverting amplifier, this is
normally ground; in a unity-gain buffer connect the
guard to the output. A convenient way of guarding the
8-pin TO-99 version of the ICL7611 is to use a 10-pin
circle, with the two extra pads on either side of the
input pins to provide space for a guard ring (see Figure
8). Assembled boards should be carefully cleaned,
and if a high humidity environment is expected, confor-
mally coated.
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