TDA4856 datasheet(13/56 Pages) PHILIPS

13 / 56 page

1999 Jul 13

Philips Semiconductors

Product speciﬁcation

I2C-bus autosync deﬂection controller for

PC monitors

TDA4856

Table 3

Activation of protection mode

When the protection mode is active, several pins of the

TDA4856 are forced into a defined state:

HDRV (horizontal driver output) is floating

BDRV (B+ control driver output) is floating

HUNLOCK (indicates, that the frequency-to-voltage

converter is out of lock) is floating (HIGH-level via

external pull-up resistor)

CLBL provides a continuous blanking signal

The capacitor at HPLL2 is discharged.

If the soft start procedure is activated via the I2C-bus, all of

these actions will be performed in a well defined sequence

(see Figs 24 and 25).

Power dip recognition

In standby mode the I2C-bus will only answer with an

acknowledge, when data is sent to control register with

subaddress 1AH. This register contains the standby and

soft start control bit.

If the I2C-bus master transmits data to another register, an

aknowledge is given after the chip address and the

subaddress; an acknowledge is not given after the data.

This indicates that only in soft start mode data can be

stored into normal registers.

If the supply voltage dips under 8.1 V the TDA4856 leaves

normal operation mode and changes into standby mode.

The microcontroller can check this state by sending data

into a register with the subaddress 0XH. The acknowledge

will only be given on the data if the TDA4856 is active.

Due to this behaviour the start-up of the TDA4856 is

defined as follows. The first data that is transferred to the

TDA4856 must be sent to the control register with

subaddress 1AH. Any other subaddress will not lead to an

acknowledge. This is a limitation in checking the

I2C-busses of the monitor during start-up.

ACTIVATION

RESET

Low supply voltage at pin 10 increase supply voltage;

reload registers;

soft start via I2C-bus

Power dip, below 8.1 V

reload registers;

soft start via I2C-bus or

via supply voltage

X-ray protection XRAY

(pin 2) triggered

reload registers;

soft start via I2C-bus

HPLL2 (pin 30) externally

pulled to ground

release pin 30

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