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Automatic Level Control (ALC)

The Automatic Level Control Block (ALC) is a variable gain amplifier (with 32 non linear discrete steps)

controlled by two analog feed backs acting at the same time. The ALC gain range is 0dB to 30 dB and

the gain change is clocked at 5KHz. Each step increases or reduces the voltage of 1dB (Typ).

Two are the control loops acting to define the ALC gain:

- A Voltage Control loop

- A Current Control Loop

The Voltage control loop acts to keep the Peak-to-Peak Voltage constant on Vsense. The gain

adjustment is related to the result of a peak detection between the Voltage waveform on Vsense and

two internal Voltage references.

The next gain level is increased by 1 step

No Gain Change

The next gain level is decreased by 1 step

The Current control loop acts to limit the maximum Peak Output current inside ATOP1 and ATOP2.

The current control loop acts through the voltage control loop decreasing the Output Peak-to-Peak

Amplitude to reduce the Current inside the Power Line Interface.

The current sensing is done by mirroring the current in the High side MOS of the Power Amplifier (not

dissipating current Sensing). The Output Current Limit (up to 400mApeak), is set by means of an

a voltage signal. The Peak current sensing block works as the Output Voltage sensing Block:

Voltage Control Loop Acting

No Gain Change

The next gain level is decreased by 1 step

Figure 13 shows the typical connection of Current anVoltage control loops.

Figure 13. Voltage and Current Feedback external interconnection Example

Voltage Control Loop Formula

R1

ALC

VOLTAGE

LOOP

CURRENT

LOOP

Vsense

CL

ATOP/ATO

1.865V (Typ)

AVss

5.6nF

R2

RCL

100pF

Vout

D03IN1421

VR

PK

R

1

R

2

+

R

2

--------------------

VCL

TH

VCL

HY ST

±

()

⋅

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