OPA830 datasheet(25/56 Pages) TI

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7.4.2 Single-Supply Operation (2.7 V to 5.4 V)

Most newer systems use a single power supply to improve efficiency and to simplify power supply design. The

OPA838 can be used with single-supply power (ground for the negative supply) with no change in performance

from split supply, as long as the input and output pins are biased within the linear operating region of the device.

The outputs nominally swing rail-to-rail with approximately a 100-mV headroom required for linear operation.

The inputs can swing below the negative rail (typically ground) and to within 1.3 V of the positive supply. For

dc-coupled, single-supply operation, the higher-gain operating applications typical of a decompensated op amp

keep the input swings less than the input swing limit to the positive supply. Typically, the 1.3-V input headroom

required to the positive supply does not limit operation.

Figure 7-10 shows an example design that takes a 0

‑V to 0.5‑V input range, level shifts the output up to 0.15 V

for a 0

‑V input using the 4.5‑V reference voltage common for 5‑V SAR ADCs, and sets the gain to produce a

4.1

‑V output swing for the 0.5‑V input swing. This example assumes a 0‑Ω source that is required to sink the

39 µA required to bias the positive input pin to produce the 0.15

‑V output for a 0‑V input. The RF and RG values

are scaled down slightly to provide bias current cancellation by matching the parallel combination of the two bias

set-up resistors on the noninverting input. Figure 7-11 illustrates an example step response for this circuit that

produces an output from 0.15 V for a 0-V input to 4.35 V for a 0.5-V input.

RF 1 NŸ

RG 56.2 Ÿ

VCC

VG1

RB2 49.9 Ÿ

VREF

V1 4.5 V

VCC 5 V

VOUT

0 V to 0.5 V

Input Swing

Figure 7-10. DC-Coupled, Single-Supply, Noninverting Interface With Output Level Shift

Time (µsec)

0.02 0.04 0.06 0.08

0.1

0.12 0.14 0.16 0.18

0.2

0.5

1.5

2.5

3.5

4.5

D065

Input

Output

Figure 7-11. Unipolar Input to Level Shifted Output Step Response

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OPA838

SBOS867D – AUGUST 2017 – REVISED SEPTEMBER 2024

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