TDA4657 Datasheet, PDF (6/17 Pages) NXP Semiconductors – Generic multi-standard decoder

Philips Semiconductors
Generic multi-standard decoder
Preliminary specification
TDA4657
and for a PAL signal in NTSC 4.4 mode. If P_IDT is positive
in SECAM mode, the scanner switches back to the PAL
mode in order to prevent a PAL signal being erroneously
identified as a SECAM signal (PAL priority).
If then P_IDT is not positive, the scanner returns to SECAM
mode and remains there if P_IDT is positive again. In the
event of a field frequency of 60 Hz the signal can not be
identified as a SECAM signal, even if P_IDT is positive. In
this event the scanner switches forward in the NTSC 4.4
mode. If the H/2 signal has the wrong polarity, the
identification signal is negative and the H/2 flip-flop is set
to the correct phase.
The third demodulator operates in NTSC mode and is
active during the burstkey pulse. The resulting
identification signal (N_IDT, pin 12) is positive for PAL and
NTSC 4.4 signals in NTSC 4.4 mode. The reference signal
has the (B−Y) phase.
The two identification signals allow an unequivocal
identification of the received signal. In the event of a signal
being identified, the scanning is stopped and after a delay
time the colour is switched on.
The standard outputs (active HIGH) are available at the
pins 17, 18 and 19. During scanning the HIGH level is
2.5 V and when a signal has been identified the HIGH level
is switched to 6 V. The standard pins can also be used as
inputs in order to force the IC into a desired mode (Forced
Standard Setting).
Sandcastle detector and pulse processing
In the sandcastle detector the super sandcastle pulse (SC)
present at pin 20 is compared with three internal threshold
levels by means of three differential amplifiers. The
derived signals are the burstkey pulse, the horizontal
blanking pulse and the combined horizontal and vertical
blanking pulse. These signals are processed into various
control pulses required for the timing of the IC.
Bandgap reference
In order to ensure that the CD output signals and the
threshold levels of the sandcastle detector are
independent of supply voltage variations a bandgap
reference voltage has been integrated.
LIMITING VALUES
In accordance with the Absolute Maximum Rating System (IEC 134).
SYMBOL
PARAMETER
T_stg
T_amb
V_P
P_tot
V₂₀
storage temperature
operating ambient temperature
supply voltage
power dissipation
voltage at pin 20
voltage at all other pins
CONDITIONS MIN. MAX. UNIT
−25 +150 °C
0 +70
°C
− 8.8
V
without load − 330
mW
I_max = 10 µA −
I_max = 100 µA −
15
V
V_P + v_be V
THERMAL RESISTANCE
SYMBOL
PARAMETER
R_{th j-a}
thermal resistance on printed-circuit board from junction to
ambient in free air (without heat spreader)
SO 20
DIL 20
THERMAL RESISTANCE
90 K/W
70 K/W
June 1993
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