TDA4886A Datasheet, PDF (17/52 Pages) NXP Semiconductors – 140 MHz video controller with I2C-bus

Philips Semiconductors
140 MHz video controller with I²C-bus
Product specification
TDA4886A
Notes to the characteristics
1. Definition of levels (see Figs 3 to 5)
Reference black level: this is the level to which the input level is clamped during the input clamping pulse
(V₅ > 3.5 V). It is used internally as a reference for the gain settings. It can be observed on the outputs:
a) When the input is at black and the brightness setting is nominal (subaddress 01H = 10H)
b) During output blanking/clamping (V₁₁ > 3.5 V) if control bit PEDST = 0.
Video black level: this is the black level of the actual video. On the input it is still equal to the reference black level.
On the output it may deviate from it according to the brightness setting. Contrast setting leaves the video black level
unaltered . Gain setting biases the video black level due to its influence on brightness. This is important for correct
grey scale tracking.
Pedestal black level: this is an ultra black level which deviates from reference black level by a fixed amount. It can
be observed on the output during output blanking/clamping (V₁₁ > 3.5 V) if control bit PEDST = 1.
Switch-off voltage: this is the lowest signal voltage at outputs. The signals will be switched off by discharging the
internal black level storage capacitors if the supply voltage is less than V_PSO.
Blanking level: this level equals reference black (control bit PEDST = 0) or pedestal black (control bit PEDST = 1).
2. Explanation to black level adjustment:
The three reference black levels are aligned correctly when they are made equal to the ‘extended cut-off levels’ of
the three cathodes. Full raster and spot cut-off can only be achieved by enabling the pedestal blanking or by applying
a negative pulse to the control grid G1.
Negative feedback for DC-coupled cathodes (control bit FPOL = 0): the actual blanking level on the outputs
depends on the external feedback application for output clamping. The loop will function correctly only if it is within
the control range of V_{22,19,16(rbl)(min)} to V_{22,19,16(rbl)(max)}. It should be noted that changing control bit PEDST in a given
application will not affect the blanking level, but instead shifts the video (and needs re-alignment of the three black
levels).
Positive feedback for AC-coupled cathodes (control bit FPOL = 1): the feedback loop for output clamping is
closed internally. The actual blanking level at the outputs depends on control bits BLH2 and BLH1 only. Four discrete
blanking levels between approximately 0.75 and 1.5 V can be chosen. It should be noted that changing control bit
PEDST will not affect the blanking level selected by control bits BLH2 and BLH1, but instead shifts the video (and
needs re-alignment of the three black levels).
3. Definition of output signals (see Fig.6):
Colour signal: all positive voltages referred to black level at signal outputs.
Nominal colour signal: colour signal with nominal input signal (0.7 V_b-w), nominal contrast setting and maximum
gain setting.
Video signal: all positive voltages referred to reference black level at signal outputs. The video signal is the
superimposing of the brightness information (∆V_bl) and the colour signal.
4. The total supply current I_P = I₇ + I₂₁ + I₁₈ + I₁₅ depends on the supply voltage with a factor of approximately 4.4 mA/V
and varies in the temperature range from −20 to +70 °C by approximately ±5% (V_22,19,16 = 0.77 V).
5. The channel supply current depends on the signal output current, the channel supply voltage and the signal output
voltage. With I_px = I_21,18,15 at V_P1,2,3 = 8 V and V_22,19,16 = 0.77 V:
I_21,18,15 ≈ I_px + I_22,19,16 + 4.4 ^m---V---A-- × ( V_P1,2,3 – 8 V) – 1 ^m---V---A-- × ( V_{22, 19, 16} – 0.77 V)
1998 Dec 04
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