OPA2836-Q1 Datasheet, PDF (26/44 Pages) Texas Instruments – Very-Low Power, Rail-to-Rail Out, Negative-Rail In, Voltage-Feedback Operational Amplifier

OPA2836-Q1
SBOS794 – DECEMBER 2016
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Device Functional Modes (continued)
Figure 59 shows a similar noninverting single-supply scenario with the reference generator replaced by the
Thevenin equivalent using resistors and the positive supply. R_G’ and R_G” form a resistor divider from the 5-V
supply and are used to bias the negative side with the parallel sum equal to the equivalent R_G to set the gain. To
cancel the voltage offset that is otherwise caused by the input bias currents, R₁ is chosen to be equal to R_F in
parallel with R_G’ in parallel with R_G” (R₁= R_F || R_G’ || R_G”). For example, if a gain of 2 is required and R_F = 1 kΩ,
selecting R_G’ = R_G” = 2 kΩ gives an equivalent parallel sum of 1 kΩ, sets the gain to 2, and references the input
to mid supply (2.5 V). R₁ is then set to 499 Ω for bias current cancellation, which can be lower cost compared to
Figure 59 but requires extra current in the resistor divider.
Signal and bias
from previous stage
V_SIG
2.5 V
R₁
R_G’
5 V _RG”
5V
OPA2836-Q1
R_O
V_OUT
GV_SIG
2.5 V
Signal and bias to
R_F
next stage
Copyright © 2016, Texas Instruments Incorporated
Figure 59. Noninverting Single Supply With Resistors
Figure 60 shows a typical inverting amplifier situation. With a 5-V single supply, a mid-supply reference generator
is needed to bias the positive side via R₁. To cancel the voltage offset that is otherwise caused by the input bias
currents, R₁ is chosen to be equal to R_F in parallel with R_G. For example, if a gain of –2 is required and R_F = 1
kΩ, select R_G = 499 Ω to set the gain and R₁ = 332 Ω for bias-current cancellation. The value for C is dependent
on the reference, but at least 0.1 µF is recommended to limit noise into the operational amplifier.
5V
2.5 V
REF
5V
R₁
C
OPA2836-Q1
R_O
VOUT
GV_SIG
2.5 V
R_G
R_F
V_SIG
2.5 V
Signal and bias to
next stage
Signal and bias
from previous stage
Copyright © 2016, Texas Instruments Incorporated
Figure 60. Inverting Single Supply With Reference
26
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