OPA344 Datasheet, PDF (11/29 Pages) Burr-Brown (TI) – LOW POWER, SINGLE-SUPPLY, RAIL-TO-RAIL OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series

performance curve “Small-Signal Overshoot vs Capacitive
Load.” In unity-gain configurations, 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 perfor-
mance 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
OPA344
V_OUT
V_IN
10Ω to
20Ω
R_L
C_L
FIGURE 5. Series Resistor in Unity-Gain Configuration
Improves Capacitive Load Drive.
DRIVING A/D CONVERTERS
The OPA344 and OPA345 series op amps are optimized for
driving medium-speed sampling A/D converters. The
OPA344 and OPA345 op amps buffer the A/D’s input
capacitance and resulting charge injection while providing
signal gain.
Figures 6 shows the OPA344 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
OPA344, the combination is ideal for space-limited, low-
power applications. In this configuration, an RC network at
the A/D’s input can be used to filter charge injection.
Figure 7 shows the OPA2344 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.
+5V
0.1µF
0.1µF
V_IN
V_IN = 0V to 5V for
0V to 5V output.
OPA344
500Ω
3300pF
8 V+
+In
2
–In
3
ADS7822
12-Bit A/D
GND 4
RC network filters high frequency noise.
FIGURE 6. OPA344 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
OPA2344
R₆
100kΩ
R₉
510kΩ
R₇
51kΩ
R₈
150kΩ
C₃
33pF
1/2
OPA2344
C₂ 1000pF
R₅
20kΩ
G = 100
Passband 300Hz to 3kHz
V_REF 1
8 ^V+
7
+IN
ADS7822 ⁶
2
–IN
12-Bit A/D ₅
3
4
DCLOCK
D_OUT
CS/SHDN
GND
Serial
Interface
FIGURE 7. Speech Bandpass Filtered Data Acquisition System.
OPA344, 2344, 4344
OPA345, 2345, 4345
11
SBOS107A
www.ti.com