TDA9885TSSLASHV3 datasheet(13/56 Pages) PHILIPS

13 / 56 page

2003 Oct 02

Philips Semiconductors

Product speciﬁcation

I2C-bus controlled single and multistandard

alignment-free IF-PLL demodulators

TDA9885; TDA9886

8.14

Audio ampliﬁer and mute time constant

The audio amplifier consists of two parts:

• AF preamplifier

• AF output amplifier.

The AF preamplifier used for FM sound is an operational

amplifier with internal feedback, high gain and high

common mode rejection. The AF voltage from the

PLL demodulator is 5 mV (RMS) for a frequency deviation

of 27 kHz and is amplified by 30 dB. By the use of a

DC operating point control circuit (with external

capacitor CAF), the AF preamplifier is decoupled from the

PLL DC voltage. The low-pass characteristic of the

amplifier reduces the harmonics of the sound intercarrier

signal at the AF output terminal.

For FM sound a switchable de-emphasis network (with

external capacitor) is implemented between the

preamplifier and the output amplifier.

The AF output amplifier provides the required AF output

level by a rail-to-rail output stage. A preceding stage

makes use of an input selector for switching between

FM sound, AM sound and mute state. The gain can be

switched between 10 dB (normal) and 4 dB (reduced).

Switching to the mute state is controlled automatically,

dependent on the digital acquisition help in case the VCO

of the FM-PLL is not in the required frequency window.

This is done by a time constant: fast for switching to the

mute state and slow (typically 40 ms) for switching to the

no-mute state.

All switching functions are controlled via the I2C-bus:

• AM sound, FM sound and forced mute

• Auto mute enable or disable

• De-emphasis off or on with 50 or 75 µs

• Audio gain normal or reduced.

8.15

Internal voltage stabilizer

The band gap circuit internally generates a voltage of

approximately 2.4 V, independent of supply voltage and

temperature. A voltage regulator circuit, connected to this

voltage, produces a constant voltage of 3.55 V which is

used as an internal reference voltage.

8.16

I2C-bus transceiver and module address

The device can be controlled via the 2-wire I2C-bus by a

microcontroller. Two wires carry serial data (SDA) and

serial clock (SCL) information between the devices

connected to the I2C-bus.

The device has an I2C-bus slave transceiver with

auto-increment. The circuit operates up to clock

frequencies of 400 kHz.

A slave address is sent from the master to the slave

receiver. To avoid conflicts in a real application with other

devices providing similar or complementing functions,

there are four possible slave addresses available. These

Module Addresses (MADs) can be selected by connecting

resistors on pin SIOMAD and/or pins SIF1 and SIF2 (see

Fig.23). Pin SIOMAD relates with bit A0 and pins SIF1

and SIF2 relate with bit A3. The slave addresses of this

device are given in Table 1.

The power-on preset value is dependent on the use of

pin SIOMAD and can be chosen for 45.75 MHz NTSC as

default (pin SIOMAD left open-circuit) or 58.75 MHz NTSC

(resistor on pin SIOMAD). In this way the device can be

used without the I2C-bus as an NTSC only device.

Remark: In case of using the device without the I2C-bus,

then the rise time of the supply voltage after switching on

power must be longer than 1.2

µs.

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