OP193 Datasheet, PDF (13/16 Pages) Analog Devices – Precision, Micropower Operational Amplifiers

OP193/OP293/OP493
From the formulas, it can be seen that if the span trim is ad-
justed before the zero trim, the two trims are not interactive,
which greatly simplifies the calibration procedure.
Calibration of the transmitter is simple. First, the slope of the
output current versus temperature is calibrated by adjusting the
span trim, R7. A couple of iterations may be required to be sure
the slope is correct.
Once the span trim has been completed, the zero trim can be
made. Remember that adjusting the zero trim will not affect the
gain.
The zero trim can be set at any known temperature by adjusting
R5 until the output current equals:
I_OUT
=


∆I_FS
∆T_OPERATING


(T_AMBIENT
− T_MIN) + 4 mA
Table I shows the values of R6 required for various temperature
ranges.
Table I. R6 Values vs. Temperature
Temp Range
R6
0°C to +70°C
–40°C to +85°C
–55°C to +150°C
10 kΩ
6.2 kΩ
3 kΩ
A Micropower Voltage Controlled Oscillator
An OP293 in combination with an inexpensive quad CMOS
analog switch forms the precision VCO of Figure 34. This cir-
cuit provides triangle and square wave outputs and draws only
50 µA from a single 5 V supply. A1 acts as an integrator; S1
switches the charging current symmetrically to yield positive and
negative ramps. The integrator is bounded by A2 which acts as
a Schmitt trigger with a precise hysteresis of 1.67 volts, set by
resistors R5, R6, and R7, and associated CMOS switches. The
resulting output of A1 is a triangle wave with upper and lower
levels of 3.33 and 1.67 volts. The output of A2 is a square wave
with almost rail-to-rail swing. With the components shown, fre-
quency of operation is given by the equation:
f_OUT = V_CONTROL (Volts) × 10 Hz/V
but this can easily be changed by varying C1. The circuit oper-
ates well up to 500 Hz.
V_CONTROL
R1
200kΩ
R2
200kΩ
R3
100kΩ
C1
75nF
+5V
2
8
A1
1
1/2 OP293
3
4
+5V
R5
200kΩ
6
A2
1/2 OP293
5
SQUARE
7 ^OUT
R4
200kΩ
R8
200kΩ
TRIANGLE
OUT
R6
200kΩ
+5V
R7
200kΩ
1 IN/OUT
2 OUT/IN
CD4066
S1
V_DD ¹⁴ _+5V
CONT 13
3 OUT/IN
S2
CONT 12
4 IN/OUT
IN/OUT 11
5 CONT
6 CONT
7 _VSS
OUT/IN 10
S3
OUT/IN 9 _+5V
S4
IN/OUT 8
Figure 34. Micropower Voltage Controlled Oscillator
A Micropower, Single-Supply Quad Voltage Output 8-Bit
DAC
The circuit of Figure 35 uses the DAC8408 CMOS quad 8-bit
DAC and the OP493 to form a single-supply quad voltage out-
put DAC with a supply drain of only 140 µA. The DAC8408 is
used in the voltage switching mode and each DAC has an out-
put resistance (≈10 kΩ) independent of the digital input code.
The output amplifiers act as buffers to avoid loading the DACs.
The 100 kΩ resistors ensure that the OP493 outputs will swing
to within 1/2 LSB of ground, i.e.:
1 _× 1.23V _{= 3 mV}
2 256
REV. A
–13–