TDA7801 datasheet(22/48 Pages) STMICROELECTRONICS

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"PLL-filter /enable" pin description

TDA7801

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DocID022674 Rev 4

"PLL-filter /enable" pin description

5.1

Functionality

The pin 2 has the functions to:



ENABLE



PLL filter

When the pin 2 is set to logic level low the TDA7801 is in standby-mode and the current

consumption is ISB. The device is waked-up and put in tristate-mode setting the same pin to

logic level high. In tristate-mode the TDA7801 is ready to receive I2C bus instructions. The

device is set in amplifier-mode writing '1' on bit D7 of byte IB1.

In amplifier-mode the PIN2 works as PLL filter pin. The TDA7801 will place this pin to have

a precise voltage value.

During the transition from amplifier-mode to standby-mode, the device will try to force the

Pin2 level sourcing a current IILENB.

5.2

Driving

In Figure 26 an applicative schematic to drive the Pin 2 is reported. In the schematic, it is

supposed that the TDA7801 is interfaced with a µP.

Figure 26. Standby driving circuit

The Rf and Cf components are respectively resistance and capacitance of the PLL filter. The

resistance R1 and diode 1N4848 allows the Pin 2 to force to logic level low and the

TDA7801 to force its voltage level in amplifier-mode. During the transition amplifier-

mode/standby-mode the TDA7801 tries to forces the voltage on the PLL/Enable by sourcing

a current flow. Since the PLL/ENABLE pin is forced at a voltage lower than VILENB in the

above described conditions, the buffer input resistance should be chosen small enough to

take this effect into account.

It’s important to keep the PLL-Filter ground as close as possible to digital ground in the

application board in order to minimize the PLL reference movement.

TDA7801 Datasheet(PDF) 22 Page - STMicroelectronics