TSH80_07 datasheet(18/24 Pages) STMICROELECTRONICS

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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 15µA, you should use a high resistance R1 (approximately 10k

Ω) to

avoid introducing an offset mismatch at the amplifier inputs.

Figure 33.

Asymmetrical supply schematic diagram

C1, C2, C3 are bypass capacitors intended to filter perturbation from VCC. The following

capacitor values are appropriate:

C1=100nF and C2=C3=100µF

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

current. Therefore, you could use the following resistance values:

R2=R3=4.7k

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

Cout). With R1=10kΩ, Rout=RL=150Ω, and Cin=2µF, Cout=220µF the cutoff frequency

obtained is lower than 10Hz.

Figure 34.

Use of the TSH8x in gain = -1 configuration

Vcc+

OUT

Cin

Cout

Vcc+

OUT

Cin

Cout

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