OPA2835 Datasheet, PDF (29/53 Pages) National Semiconductor (TI) – Ultra Low-Power, Rail-to-Rail Out, Negative Rail In, VFB Op Amp

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+2.5 V
OPA835
OPA2835
SLOS713E – JANUARY 2011 – REVISED JULY 2013
V_SIG
R_G
OPA 835
V_OUT
Load
-2.5 V
R_F
Figure 61. Split Supply Operation
Single-Supply Operation (2.5V to 5.5V)
Many newer systems use single power supply to improve efficiency and reduce the cost of the power supply.
OPA835 and OPA2835 are designed for use with single-supply power operation and can be used with single-
supply power with no change in performance from split supply as long as the input and output are biased within
the linear operation of the device.
To change the circuit from split supply to single supply, level shift of all voltages by ½ the difference between the
power supply rails. For example, changing from ±2.5 V split supply to 5 V single supply is shown conceptually in
Figure 62.
5V
V_SIG
R_G
OPA 835
V_OUT
Load
R_F
2.5 V
Figure 62. Single Supply Concept
A more practical circuit will have an amplifier or other circuit before to provide the bias voltage for the input and
the output provides the bias for the next stage.
Figure 63 shows a typical non-inverting amplifier situation. With 5V single supply, a mid supply reference
generator is needed to bias the negative side via R_G. To cancel the voltage offset that would otherwise be
caused by the input bias currents, R₁ is chosen to be equal to R_F in parallel with R_G. For example if gain of 2 is
required and R_F = 2 kΩ, select R_G = 2 kΩ to set the gain and R₁ = 1 kΩ for bias current cancellation. The value
for C is dependent on the reference, but at least 0.1µF is recommended to limit noise.
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