OPA2348-HIREL Datasheet, PDF (12/14 Pages) Texas Instruments – 1-MHz, 45-μA CMOS RAIL-TO-RAIL OPERATIONAL AMPLIFIER

OPA2348-HiRel
SBOS482 – NOVEMBER 2009
www.ti.com
Driving Analog-to-Digital Converters (ADCs)
The OPA2348 op amps are optimized for driving medium-speed sampling ADCs. The OPA2348 op amps buffer
the ADC input capacitance and resulting charge injection while providing signal gain.
Figure 7 shows the OPA2348 in a basic noninverting configuration driving the ADS7822. The ADS7822 is a
12-bit, micropower sampling converter in the MSOP-8 package. When used with the low-power miniature
packages of the OPA348, the combination is ideal for space-limited, low-power applications. In this configuration,
an RC network at the ADC input can be used to provide for anti-aliasing filter and charge injection current.
+5V
0.1µF
0.1µF
V_IN
V_IN = 0 V to 5 V for
0-V to 5-V output.
1/2
OPA2348
500W
3300pF
8 V+
+In
2
–In
3
ADS7822
12-Bit A/D
GND 4
RC network filters high-frequency noise.
1 V_REF
7
DCLOCK
6
D_OUT
5
CS/SHDN
Serial
Interface
NOTE: A/D Input = 0 to V _REF
Figure 7. Noninverting Configuration Driving ADS7822
The OPA2348 can also be used in noninverting configuration driving ADS7822 in limited low-power applications.
In this configuration, an RC network at the ADC input can be used to provide for antialiasing filter and charge
injection current. See Figure 7 for the OPA2348 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 operates with V_S = 2.7 V to 5 V with less than 250-μA
typical quiescent current.
V+ = +2.7V to 5V
Passband 300Hz to 3kHz
R₁
1.5kW
C₁
1000pF
R₂
1MW
Electret
Microphone⁽¹⁾
R₃
1MW
R₄
20kW
1/2
OPA2348
R₆
100kΩ
R₉
510kW
R₇
51kW
R₈
150kW
C₃
33pF
1/2
OPA2348
C₂ 1000pF
R₅
20kW
G = 100
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
(1) Electret microphone powered by R₁.
Figure 8. Speech Bandpass Filtered Data Acquisition System
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