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OPA342 Datasheet, PDF (10/15 Pages) Burr-Brown (TI) – Low Cost, Low Power, Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series | |||
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Overshoot vs Capacitive Load.â In unity-gain configura-
tions, capacitive load drive can be improved by inserting a
small (10⦠to 20â¦) resistor, RS, in series with the output, as
shown in Figure 5. This significantly reduces ringing while
maintaining dc performance for purely capacitive loads.
However, if there is a resistive load in parallel with the
capacitive load, a voltage divider is created, introducing a dc
error at the output and slightly reducing the output swing.
The error introduced is proportional to the ratio RS/RL, and
is generally negligible.
V+
RS
OPA342
VOUT
VIN
10⦠to
20â¦
RL
CL
DRIVING A/D CONVERTERS
The OPA342 series op amps are optimized for driving
medium-speed sampling ADCs. The OPA342 op amps buffer
the ADCâs input capacitance and resulting charge injection
while providing signal gain.
Figures 6 shows the OPA342 in a basic noninverting con-
figuration driving the ADS7822. The ADS7822 is a 12-bit,
micro-power sampling converter in the MSOP-8 package.
When used with the low-power, miniature packages of the
OPA342, the combination is ideal for space-limited, low-
power applications. In this configuration, an RC network at
the ADCâs input can be used to filter charge injection.
Figure 7 shows the OPA2342 driving an ADS7822 in a
speech bandpass filtered data acquisition system. This small,
low-cost solution provides the necessary amplification and
signal conditioning to interface directly with an electret
microphone. This circuit will operate with VS = +2.7V to
+5V with less than 500µA quiescent current.
FIGURE 5. Series Resistor in Unity-Gain Configuration
Improves Capacitive Load Drive.
+5V
0.1µF
0.1µF
VIN
VIN = 0V to 5V for
0V to 5V output.
OPA342
500â¦
3300pF
8 V+
+In
2
âIn
3
ADS7822
12-Bit A/D
GND 4
RC network filters high frequency noise.
FIGURE 6. OPA342 in Noninverting Configuration Driving ADS7822.
1 VREF
7
DCLOCK
6
DOUT
5
CS/SHDN
Serial
Interface
NOTE: A/D Input = 0 to VREF
R1
1.5kâ¦
R2
1Mâ¦
C1
1000pF
Electret
Microphone(1)
R3
1Mâ¦
NOTE: (1) Electret microphone
powered by R1.
V+ = +2.7V to 5V
R4
20kâ¦
1/2
OPA2342
R6
100kâ¦
R9
510kâ¦
R7
51kâ¦
R8
150kâ¦
C3
33pF
1/2
OPA2342
C2 1000pF
R5
20kâ¦
G = 100
Passband 300Hz to 3kHz
VREF 1
8 V+
7
+IN
ADS7822 6
2
âIN
12-Bit A/D 5
3
4
DCLOCK
DOUT
CS/SHDN
GND
Serial
Interface
FIGURE 7. Speech Bandpass Filtered Data Acquisition System.
10
OPA342, 2342, 4342
SBOS106A
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