TS4994FC datasheet(27/35 Pages) STMICROELECTRONICS

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TS4994FC

Application information

27/35

The two following graphs show typical applications of the TS4994 with a random selection of

four

ΔR/R values with a 0.1% tolerance.

4.6

CMRR performance

For calculating CMRR performance, we consider that Cin and Cfeed have no influence. Cb

has no influence in the calculation of the CMRR.

We use the same kind of resistor (same tolerance) and

ΔR is the tolerance value in %.

The following CMRR equation is valid for frequencies ranging from DC to about 1kHz.

The CMRR equation is (

ΔR in %):

Example: With

ΔR = 1%, the minimum CMRR is -34dB.

This example is a worst case scenario where each resistor has extreme tolerance. Ut

illustrates the fact that for CMRR, good matching is essential.

As with the PSRR, due to self-generated noise, the TS4994 CMRR limitation is about

-110dB.

Figure 94 and Figure 95 show CMRR versus frequency and versus bypass capacitor Cb in

worst-case conditions (

ΔR=0.1%).

Figure 92.

PSRR vs. frequency with random

choice condition

Figure 93.

PSRR vs. frequency with random

choice condition

100

1000

10000

-140

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Cb=0.1

μF

Cb=1

μF

Cb=0

20k

Cb=0.47

μF

Vcc = 5V, Vripple = 200mVpp

Av = 1, Cin = 4.7

μF

ΔR/R ≤ 0.1%, RL ≥ 8Ω

Tamb = 25

°C, Inputs = Grounded

Frequency (Hz)

100

1000

10000

-140

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Cb=0.1

μF

Cb=1

μF

Cb=0

20k

Cb=0.47

μF

Vcc = 2.5V, Vripple = 200mVpp

Av = 1, Cin = 4.7

μF

ΔR/R ≤ 0.1%, RL ≥ 8Ω

Tamb = 25

°C, Inputs = Grounded

Frequency (Hz)

)

(

)

10000

(

200

Log

CMRR

2 ⎥

⎦

⎤

⎢

⎣

⎡

−

≤

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