OPA835_1110 Datasheet, PDF (31/49 Pages) Texas Instruments – Ultra Low-Power, Rail-to-Rail Out, Negative Rail In, VFB Op Amp

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OPA835
OPA2835
SLOS713D – JANUARY 2011 – REVISED OCTOBER 2011
5V
2.5 V
REF
5V
R₁
C
OPA 835
R_O
VOUT
GV_SIG
2.5 V
R_G
R_F
V_SIG
2.5 V
Signal and bias
from previous stage
Signal and bias to
next stage
Figure 65. Inverting Single Supply with Reference
Figure 66 shows a similar inverting single supply scenario with the reference generator replaced by the Thevenin
equivalent using resistors and the positive supply. R₁ and R₂ form a resistor divider from the 5V supply and are
used to bias the positive side. To cancel the voltage offset that would otherwise be caused by the input bias
currents, set the parallel sum of R₁ and R₂ equal to the parallel sum of R_F and R_G. C should be added to limit
coupling of noise into the positive input. For example if gain of –2 is required and R_F = 2 kΩ, select R_G = 1 kΩ to
set the gain. R₁ = R₂ = 1.33 kΩ for mid supply voltage bias and for op amp input bias current cancellation. A
good value for C is 0.1µF. This can be lower cost, but note the extra current draw required in the resistor divider.
5V
5V
R₁
R_O
R₂
OPA 835
C
V_OUT
GV_SIG
2.5 V
R_G
V_SIG
2.5 V
R_F
Signal and bias to
next stage
Signal and bias
from previous stage
Figure 66. Inverting Single Supply with Resistors
Pulse Application with Single-Supply
For pulsed applications, where the signal is at ground and pulses to some positive or negative voltage, the circuit
bias voltage considerations are different than with a signal that swings symmetrical about a reference point and
the circuit configuration should be adjusted accordingly. Figure 67 shows a pulsed situation where the signal is at
ground (0 V) and pulses to a positive value.
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