AK4254 Datasheet, PDF (12/22 Pages) Asahi Kasei Microsystems – Capacitor-less Video Amp with 7:2 Video Switch

ASAHI KASEI
[AK4254]
SEL22 bit SEL21 bit SEL20 bit
VOUT2 pin
0
0
0
Off Note: 16) (default)
0
0
1
VIN1
0
1
0
VIN2
0
1
1
VIN3
1
0
0
VIN4
1
0
1
VIN5
1
1
0
VIN6
1
1
1
VIN7
Note: 16. When the input setting is “Off”, VOUT2 output is “GND”.
Table 8. Input Selector 2 (Serial Control Mode)
■ Video Block
The Video Amp has drivability for a load resistance of 150Ω. The AK4254 has composite input and output with low pass
filter (LPF). Internal negative power supply circuit supplies the negative voltage to the video amp and the video amp 0V
output is used for a pedestal level. Therefore, the output coupling capacitor can be removed.
The negative power supply circuit needs capacitors of Ca and Cb with 1.0μ, which should have the low ESR (Equivalent
Series Resistance). When those capacitors have the polarity, each positive polarity pins should be connected to CP and
VSS side.
The negative power supply circuit generates the negative voltage to use the clock that corresponds to the input video
signal. When there is no video input signal and the negative voltage is insufficient (CVEE > -0.8V) in case of low quality
input signal (Note: 17), the negative power supply circuit generates the negative voltage by using the internal oscillator
circuit. The VOUT outputs –0.6V(typ) when there is no video signal input.
Note: 17. Low quality video signal has the following characteristics.
Input Sync Tip Level= -0.43V~ -0.14V (from the pedestal voltage)
Horizontal Line Sync Pulse=4.0μs ∼5.4μs, Equalizing Pulse=2.0μs ∼2.7μs, Serration Pulse=4.0μs ∼5.4μs
AK4254
CVDD1
Charge
Pump
Negative Power
CP1
CN1 CVSS1
CVEE1
Cb
(+)
1uF
1uF Ca
(+)
Figure 3. Negative Power Supply Circuit
MS0586-E-01
- 12 -
2007/08