bt865a Conexant Systems, Inc., bt865a Datasheet - Page 57

• Manufacturer Part Number: bt865a
• Description: Ycrcb To Ntsc/pal Digital Video Encoder
• Manufacturer: Conexant Systems, Inc.

Bt864A/Bt865A Data Sheet
Figure 3-2. Example Power Plane Layout
3.3
3.3.1
3.3.2
3.3.3
100138C
02/17/03
Decoupling
Device Decoupling
Power Supply Decoupling
COMP Decoupling
For optimum performance, all capacitors should be located as close as possible to the
device, and the shortest possible leads (consistent with reliable operation) should be
used to reduce the lead inductance. Chip capacitors are recommended for minimum
lead inductance. Radial lead ceramic capacitors may be substituted for chip capacitors
and are better than axial lead capacitors for self-resonance. Values are chosen to have
self-resonance above the pixel clock.
The best power supply performance is obtained with a 0.1
decoupling each group of VDD pins to GND, and the VAA pin to AGND. The
capacitors should be placed as close as possible to the device VAA, VDD, AGND, and
GND pins and connected with short, wide traces.
The 47
the 0.1
When a linear regulator is used, the power-up sequence must be verified to prevent
latchup. A linear regulator is recommended to filter the analog power supply if the
power supply noise is greater than or equal to 200 mV . This is especially important
when a switching power supply is used, and the switching frequency is close to the
raster scan frequency. About 5% of the power supply hum and ripple noise less than
1 MHz will couple onto the analog outputs.
The COMP pin must be decoupled to the VAA pin, typically with a 0.1
capacitor. Low-frequency supply noise will require a larger value. The COMP capacitor
must be as close as possible to the COMP and the VAA pin. A surface-mount ceramic chip
capacitor is preferred for minimal lead inductance. Lead inductance degrades the noise
rejection of the circuit. Short, wide traces will also reduce lead inductance.
µ
µ
F capacitors are for high-frequency power supply noise rejection.
F capacitor shown in
Conexant
13
864A/865A
Analog
CONN
Figure 3-1
1
Ferrite
Bead
is for low-frequency power supply ripple;
µ
F ceramic capacitor
100138_029
PC Board Considerations
µ
F ceramic
3-3