OPA342_06 Datasheet, PDF (10/13 Pages) Burr-Brown (TI) – Low-Cost, Low-Power, Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series

Overshoot vs Capacitive Load.” In unity-gain configura-
tions, capacitive load drive can be improved by inserting a
small (10Ω to 20Ω) resistor, R_S, 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 R_S/R_L, and
is generally negligible.
V+
R_S
OPA342
V_OUT
V_IN
10Ω to
20Ω
R_L
C_L
DRIVING A/D CONVERTERS
The OPA342 series op amps are optimized for driving
medium-speed sampling ADCs. The OPA342 op amps buffer
the ADC’s 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 ADC’s 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 V_S = +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
V_IN
V_IN = 0V to 5V for
0V to 5V output.
OPA342
500Ω
3300pF
8 V+
+In
2
–In
3
ADS7822
12-Bit A/D
GND 4
RC network filters high frequency noise.
FIGURE 6. OPA342 in Noninverting Configuration Driving ADS7822.
1 V_REF
7
DCLOCK
6
D_OUT
5
CS/SHDN
Serial
Interface
NOTE: A/D Input = 0 to V_REF
R₁
1.5kΩ
R₂
1MΩ
C₁
1000pF
Electret
Microphone⁽¹⁾
R₃
1MΩ
NOTE: (1) Electret microphone
powered by R₁.
V+ = +2.7V to 5V
R₄
20kΩ
1/2
OPA2342
R₆
100kΩ
R₉
510kΩ
R₇
51kΩ
R₈
150kΩ
C₃
33pF
1/2
OPA2342
C₂ 1000pF
R₅
20kΩ
G = 100
Passband 300Hz to 3kHz
V_REF 1
8 ^V+
7
+IN
2
–IN
ADS7822 ⁶
12-Bit A/D ₅
3
4
DCLOCK
D_OUT
CS/SHDN
GND
Serial
Interface
FIGURE 7. Speech Bandpass Filtered Data Acquisition System.
10
OPA342, 2342, 4342
SBOS106A