DocID009413 Rev 10

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TSH80, TSH82

Precautions on asymmetrical supply operation

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Precautions on asymmetrical supply operation

The TSH8x device 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, use a high resistance R1 (approximately 10 k

Ω) to avoid

introducing an offset mismatch at the amplifier’s inputs.

Figure 34. 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 running through them must be superior to 100 times the

bias current. Therefore, use the following resistance values:

R2 = R3 = 4.7 k

Ω

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 = 2 µF, Cout = 220 µF the cutoff

frequency obtained is lower than 10 Hz.

Figure 35. Use of the TSH8x in a gain = -1 configuration

IN

R1

OUT

R2

R3

C1

C3

+

-

R4

C2

R5

Cf

RL

Cin

Cout

AM00845

Vcc+

IN

R1

OUT

R2

R3

C1

C3

+

-

C2

AM00846