TDA4856 Datasheet, PDF (13/56 Pages) NXP Semiconductors – I2C-bus autosync deflection controller for PC monitors

Philips Semiconductors
I²C-bus autosync deflection controller for
PC monitors
Product specification
TDA4856
Table 3 Activation of protection mode
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
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.
1999 Jul 13
13