OPA330 Datasheet, PDF (10/29 Pages) Texas Instruments – 50mV VOS, 0.25mV/°C, 35mA CMOS OPERATIONAL AMPLIFIERS Zerø-Drift Series

OPA330
OPA2330
OPA4330
SBOS432D – AUGUST 2008 – REVISED JUNE 2010
ACHIEVING OUTPUT SWING TO THE OP
AMP NEGATIVE RAIL
Some applications require output voltage swings from
0V to a positive full-scale voltage (such as +2.5V)
with excellent accuracy. With most single-supply op
amps, problems arise when the output signal
approaches 0V, near the lower output swing limit of a
single-supply op amp. A good single-supply op amp
may swing close to single-supply ground, but will not
reach ground. The output of the OPA330, OPA2330,
and OPA4330 can be made to swing to ground, or
slightly below, on a single-supply power source. To
do so requires the use of another resistor and an
additional, more negative, power supply than the op
amp negative supply. A pull-down resistor may be
connected between the output and the additional
negative supply to pull the output down below the
value that the output would otherwise achieve, as
shown in Figure 20.
V+ = +5V
OPA330
V_OUT
V_IN
R_P = 20kW
Op Amp V- = GND
-5V
Additional
Negative
Supply
Figure 20. For V_OUT Range to Ground
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The OPA330, OPA2330, and OPA4330 have an
output stage that allows the output voltage to be
pulled to its negative supply rail, or slightly below,
using the technique previously described. This
technique only works with some types of output
stages. The OPA330, OPA2330, and OPA4330 have
been characterized to perform with this technique; the
recommended resistor value is approximately 20kΩ.
Note that this configuration will increase the current
consumption by several hundreds of microamps.
Accuracy is excellent down to 0V and as low as
–2mV. Limiting and nonlinearity occurs below –2mV,
but excellent accuracy returns as the output is again
driven above –2mV. Lowering the resistance of the
pull-down resistor will allow the op amp to swing even
further below the negative rail. Resistances as low as
10kΩ can be used to achieve excellent accuracy
down to –10mV.
APPLICATION CIRCUITS
Figure 21 shows the basic configuration for a bridge
amplifier.
A low-side current shunt monitor is shown in
Figure 22.
V_EX
RR
RR
R₁
+5V
OPA330
V_OUT
R₁
V_REF
Figure 21. Single Op Amp Bridge Amplifier
Load
V
I_LOAD
R_SHUNT
1W
R₁
4.99kW
R₃
4.99kW
+5V
R₂
49.9kW
OPA330
R₄
48.7kW
3V
REF3130
R₆
71.5kW
R_N
56W
ADS1100
R_N
I²C
56W
Stray Ground-Loop Resistance
R₇
1.18kW
(PGA Gain = 4)
FS = 3.0V
NOTE: 1% resistors provide adequate common-mode rejection at small ground-loop errors.
Figure 22. Low-Side Current Monitor
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