LMP7717 datasheet(26/56 Pages) TI

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If ac-coupling is acceptable, a simple way to operate single-supply is to run inverting. Figure 7-12 shows a

low-power, high-gain example. In this example, a gain of –20 V/V is implemented (inverting usually does not

matter for ac-coupled channels) where the V+ input is biased midscale. This example is showing an optional

bias-current cancellation setup, which is not necessary unless the output dc level requires good accuracy. The

parallel combination of the divider resistors plus the 80.7

‑Ω isolating resistor match the feedback resistor value.

With the blocking capacitor at the inverting input, the feedback resistor impedance must be matched to achieve

bias current cancellation. In this 3-V supply example, the two inputs and the output are biased at 1.5 V. This

places the input pins in range and centers the output for maximum V PP available. Figure 7-13 illustrates the

small-signal response for this example showing a f–3dB range from a low-end cutoff of 887 Hz set by the input

capacitor value to a 17.5-MHz high-frequency cutoff.

RF 3.57 NŸ

1.5 V

DC Out

RG 178 Ÿ

U1 OPA838

VM1

C1 1 µF

VCC

V1 3 V

C2 1µF

Riso 80.6

RB1 6.98 NŸ

VG1

887 Hz to

17.5 Mhz gain

of -20 V/V

Figure 7-12. Single-Supply Inverting Gain Stage With AC-Coupled Input

Frequency (Hz)

100

10k

100k

10M

100M

D069

Output

Figure 7-13. Inverting Single-Supply Response With AC-Coupled Input

These are only two of the many ways a single-supply design can be implemented. Many other methods exist,

where using a dc reference voltage or ac-coupling are common. A good compilation of options can be found in

Single-Supply Op Amp Design Techniques.

OPA838

SBOS867D – AUGUST 2017 – REVISED SEPTEMBER 2024

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