STV0056 datasheet(3/26 Pages) STMICROELECTRONICS

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Pin Number

Name

Function

A 12V

Audio 12V Supply

AMPLK R

Amplitude Detector Capacitor Left

DET R

FM PLL Filter Right

U75 R

Deemphasis Time Constant Right

CPUMP R

FM PLL Charge Pump Capacitor Right

IREF

Current Reference Resistor

PK OUT R

Noise Reduction Peak Detector Output Right

PK OUT L

Noise Reduction Peak Detector Output Left

LEVEL L

Noise Reduction Level Left

PK IN L

Noise Reduction Peak Detector Input

FC L

Audio Roll-off Left

A GND R

Audio Ground

PIN ASSIGNMENT (continued)

SOUND DETECTION

FMIN

This is the input to the two FM demodulators. It

feeds two AGC amplifiers with a bandwidth of at

least 5-10MHz. There is one amplifier for each

channel both with the same input. The AGC ampli-

fiers have a 0dB to +40dB range.

ZIN =5k

Ω, Min input = 2mVPP per subcarrier.

Max input = 500mVPP (max when all inputs are

added together, when their phases coincide).

AGC L, AGC R

AGC amplifiers peak detector capacitor connec-

tions. The output current has an attack/decay ratio

of 1:32. That is the ramp up current is approxi-

mately 5

µA and decay current is approximately

160

µA. 11V gives maximum gain. These pins are

also driven by a circuit monitoring the voltage on

AMPLK L and AMPLK R respectively.

AMPLK L, AMPLK R

The outputs of amplitude detectors LEFT and

RIGHT. Each requires a capacitor and a resistor to

GND. The voltage across this is used to decide

whether there is a signal being received by the FM

detector. The level detector output drives a bit in

the detector I

2C bus control block.

AMPLK L and AMPLK R drive also respectively

AGC L and AGC R. For instance when the voltage

on AMPLK L is > (VREF +1 VBE) it sinks current to

VREF from pin AGCL to reduce the AGC gain.

DET L, DET R

Respectively the outputs of the FM phase detector

left and right.

This is for the connection of an external loop filter

for the PLL. The output is a push-pull current

source.

CPUMP L, CPUMP R

The output from the frequency synthesizer is a

push-pull current source which requires a capacitor

to ground to derive a voltage to pull the VCO to the

target frequency. The output is

±100µA to achieve

lock and

±2µA during lock to providea trackingtime

constant of approximately 10Hz.

VREF

This is the audio processor voltage reference used

through out the FM/audio section of the chip. As

such it is essential that it is well decoupled to

ground to reduce as far as possible the risk of

crosstalk and noise injection. This voltage is de-

rived directly from the bandgap reference of 2.4V.

The VREF output can sink up to 500

µA in normal

operation and 100

µA when in stand-by.

IREF

This is a buffered VREF output to an off-chip resistor

to produce an accurate current reference, within

the chip, for the biasing of amplifiers with current

outputs into filters. It is also required for the Noise

reduction circuit to provide accurate roll-off fre-

quencies. This pin should not be decoupled as it

would inject current noise. The target current is

µA ±2% thus a 47.5kΩ ±1% is required.

PIN DESCRIPTION

STV0056A

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