TSH80 datasheet(19/27 Pages) STMICROELECTRONICS

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TSH80, TSH81, TSH82, TSH84

Precautions on asymmetrical supply operation

Doc ID 9413 Rev 5

19/27

Precautions on asymmetrical supply operation

The TSH8x can be used with either 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 so as to reject any noise present on the supply rail.

As the bias current is 15 µA, you should use a high resistance R1 (approximately 10 k

Ω) to

avoid introducing an offset mismatch at the amplifier’s inputs.

Figure 33.

Asymmetrical supply schematic diagram

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

capacitor values are appropriate.

C1 = 100 nF and C2 = C3 = 100 µF

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 = 10 kΩ, Rout =RL = 150 Ω, and Cin =2µF, Cout = 220 µF the cutoff

frequency obtained is lower than 10 Hz.

Figure 34.

Use of the TSH8x in a gain = -1 configuration

OUT

Cin

Cout

AM00845

Vcc+

OUT

Cin

Cout

AM00846

Vcc+

1 k

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