Precautions on Asymmetrical Supply Operation

TSH80-TSH81-TSH82

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Precautions on Asymmetrical Supply Operation

The TSH8X can be used either with a dual or a single supply. If a single supply is used, the

inputs are biased to the mid-supply voltage (+Vcc/2). This bias network must be carefully

designed, in order to reject any noise present on the supply rail.

As the bias current is 15uA, you must carefully choose the resistance R1 not to introduce an

offset mismatch at the amplifier inputs.

R1=10k

Ω will be convenient. C1, C2, C3 are bypass capacitors from perturbation on Vcc as

well as for the input and output signals. We choose C1=100nF and C2=C3=100uF.

R2, R3 are such that the current through them must be superior to 100 times the bias current.

So, we take R2=R3=4.7k

Ω.

Cin, as Cout are chosen to filter the DC signal by the low pass filters (R1,Cin) and (Rout, Cout).

By taking R1=10k

Ω, RL=150Ω, and Cin=2uF, Cout=220uF we provide a cutoff frequency below

10Hz.

Some precautions have to be added, specially for low power supply application.

A feedback capacitance Cf should be added for better stability.

The table summarizes the impact of the capacitance Cf on the phase margin of the circuit.

Figure 33. Use of the TSH8x in gain = -1 configuration

IN

R1

Vcc+

OUT

R2

R3 C1

C3

C2

Cin

Cout

+

-

Cf

R5

R4

RL

IN

R1

Vcc+

OUT

R2

R3

C1

C3

C2

Cin

Cout

+

-

1k

Cf

1k

RL