OP193FSZ Datasheet, PDF (13/20 Pages) Analog Devices – Precision, Micropower Operational Amplifiers

OP193/OP293
FUNCTIONAL DESCRIPTION
The OP193/OP293 operational amplifiers are single-supply,
micropower, precision amplifiers whose input and output ranges
both include ground. Input offset voltage (VOS) is only 100 μV
maximum, while the output delivers ±5 mA to a load. Supply
current is only 15 μA.
A simplified schematic of the input stage is shown in Figure 26.
The input transistors, Q1 and Q2, are PNP devices, which permit
the inputs to operate down to ground potential. The input transis-
tors have resistors in series with the base terminals to protect
the junctions from overvoltage conditions. The second stage is
an NPN cascode that is buffered by an emitter follower before
driving the final PNP gain stage.
The OP193 includes connections to taps on the input load resis-
tors, which can be used to null the input offset voltage, VOS.
The OP293 have two additional transistors, Q7 and Q8. The
behavior of these transistors is discussed in the Output Phase
Reversal—OP193 and Output Phase Reversal—OP293 sections.
The output stage, shown in Figure 25, is a noninverting NPN
totem-pole configuration. Current is sourced to the load by
Emitter Follower Q1, while Q2 provides current sink capability.
When Q2 saturates, the output is pulled to within 5 mV of
ground without an external pull-down resistor. The totem-pole
output stage supplies a minimum of 5 mA to an external load,
even when operating from a single 3.0 V power supply.
+INPUT 2kΩ
2kΩ
–INPUT
I1
Q1
Q2
V+
FROM
INPUT
STAGE
Q4
Q1
Q5
Q3
OUTPUT
Q2
I3
I2
I1
V–
Figure 25. OP193/OP293 Equivalent Output Circuit
By operating as an emitter follower, Q1 offers a high impedance
load to the final PNP collector of the input stage. Base drive to
Q2 is derived by monitoring Q1’s collector current. Transistor
Q5 tracks the collector current of Q1. When Q1 is on, Q5 keeps
Q4 off, and Current Source I1 keeps Q2 turned off. When Q1 is
driven to cutoff (that is, the output must move toward V−), Q5
allows Q4 to turn on. Q4’s collector current then provides the
base drive for Q3 and Q2, and the output low voltage swing is
set by Q2’s VCE,SAT, which is about 5 mV.
DRIVING CAPACITIVE LOADS
The OP193/OP293 amplifiers are unconditionally stable with
capacitive loads less than 200 pF. However, the small signal,
unity-gain overshoot improves if a resistive load is added. For
example, transient overshoot is 20% when driving a 1000 pF,
10 kΩ load. When driving large capacitive loads in unity-gain
configurations, an in-the-loop compensation technique is
recommended, as illustrated in Figure 30.
V+
I2
I3 I4
Q5
Q6
OP293
ONLY
Q7
Q4
Q3
Q8
TO
OUTPUT
D1
STAGE
R1_A
R2_A
I5
R1_B
R2_B
NULLING
TERMINALS
(OP193 ONLY)
Figure 26. OP193/OP293 Equivalent Input Circuit
I6
V–
Rev. C | Page 13 of 20