SA575DTBR2G Datasheet, PDF(5/16 Page) ON Semiconductor

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SA575DTBR2G Datasheet, PDF (5/16 Pages) ON Semiconductor – Low Voltage Compandor

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SA575

Expandor

The typical expandor configuration is shown in Figure 2.

The variable gain cell and the rectifier cell are in the signal

input path. The VREF is always 1/2 VCC to provide the

maximum headroom without clipping. The 0 dB ref is

100 mVRMS. The input is AC coupled through C5, and the

output is AC coupled through C3. If in a system the inputs

and outputs are AC coupled, then C3 and C5 can be

eliminated, thus requiring only one external component,

C4. The variable gain cell and rectifier cell are DC coupled

so any offset voltage between Pins 4 and 9 will cause small

offset error current in the rectifier cell. This will affect the

accuracy of the gain cell. This can be improved by using an

extra capacitor from the input to Pin 4 and eliminating the

DC connection between Pins 4 and 9.

The expandor gain expression and the attack and release

time constant is given by Equation 1 and Equation 2,

respectively.

Expandor gain =

4VIN(avg) 2

3.8 kW x 100 mA

(eq. 1)

where VIN(avg) = 0.95VIN(RMS)

tR = tA = 10 kW x CRECT = 10 kW x C4

(eq. 2)

EXP IN

9, 11

10mF

10kW

7, 13

10kW

6, 14

4, 16

3.8kW

5, 15

2.2mF

VREF

10mF

Figure 2. Typical Expandor Configuration

EXP OUT

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