OPA4344EA BURR-BROWN [Burr-Brown Corporation], OPA4344EA Datasheet - Page 11

• Manufacturer Part Number: OPA4344EA
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

FIGURE 5. Series Resistor in Unity-Gain Configuration
FIGURE 6. OPA344 in Noninverting Configuration Driving ADS7822.
performance curve “Small-Signal Overshoot vs Capacitive
Load.” In unity-gain configurations, capacitive load drive
can be improved by inserting a small (10 to 20 ) resistor,
R
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
FIGURE 7. Speech Bandpass Filtered Data Acquisition System.
S
, in series with the output, as shown in Figure 5. This
V
IN
Microphone
NOTE: (1) Electret microphone
powered by R
Electret
Improves Capacitive Load Drive.
OPA344
V
0V to 5V output.
1.5k
IN
R
(1)
V+
= 0V to 5V for
1
1
.
V
IN
1000pF
C
1M
1M
R
R
1
2
3
S
10 to
/R
20
R
RC network filters high frequency noise.
L
S
, and is generally negligible.
OPA344
20k
20k
R
R
OPA2344
5
4
R
1/2
L
100k
R
6
500
G = 100
3300pF
C
L
51k
V+ = +2.7V to 5V
R
7
V
C
OUT
2
150k
1000pF
R
+In
8
11
2
–In
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
+5V with less than 500 A quiescent current.
3
8
OPA2344
+5V
510k
12-Bit A/D
ADS7822
33pF
R
1/2
C
V+
0.1 F
9
3
GND
4
+IN
2
–IN
Passband 300Hz to 3kHz
V
CS/SHDN
REF
DCLOCK
3
1
OPA344, 2344, 4344
OPA345, 2345, 4345
12-Bit A/D
ADS7822
1
D
V
0.1 F
OUT
NOTE: A/D Input = 0 to V
REF
4
8
7
6
5
V +
GND
7
6
5
DCLOCK
D
CS/SHDN
OUT
Interface
Serial
REF
Serial
Interface
S
= +2.7V to
®