CX25870/871
3.0 PC Board Considerations
Flicker-Free Video Encoder with Ultrascale Technology
3.6 Applications Information
Table 3-3. Hardware Modifications to Bt868/869-based PCB Required to Accommodate the CX25870/871 (2 of 3)
49
VDDMAX
VDD_VREF
Pin 49 has been renamed for the CX25870/1. For 3.3V swings on the interface signals
for CX25870/1-designs, this pin should be tied directly to 3.3V as was the case with
Bt868/9-designs.
For lower voltage swings for the digital interface signals, using a voltage divider circuit
or some other method, tie the CX25870/871’s VDD_VREF input (pin 49) to (VDDL / 2).
See Figure 3-5 for an illustration of this concept.
50
51
52
PAL
PAL
If the desired video output at power-up is PAL, then a 10 kΩ pull-up resistor is
recommended for this pin for CX25870/1-designs. No pull-up resistor was advocated
for Bt868/9-designs. If the desired video output at power-up is NTSC, then this pin
should be tied directly to GND.
SLAVE
SLEEP
SLAVE
SLEEP
If desired interface at power-up is slave or pseudo-master (i.e. slave video timing), then
a 10 kΩ pull-up resistor is recommended for this pin for CX25870/1-designs. No
pull-up resistor was advocated for Bt868/9-designs. If desired interface at power-up is
master (i.e. master video timing), then this pin should be tied directly to GND.
If desired power management state at power-up is Normal Operation, then this pin
should be tied directly to GND. If desired power management state at power-up is
Sleep, then a 10 kΩ pull-up resistor is recommended for this pin for
CX25870/1-designs. No pull-up resistor was advocated for Bt868/9-designs.
62
63
XTALOUT
XTALIN
XTALOUT
XTALIN
The recommended capacitor value from XTALIN to GND has been altered from 33 pF to
27 pF for a 20 pF load crystal. This ensures an output-to-input voltage gain sufficient to
make up signal losses through the crystal since the ratio of
CXTALOUT / CXTALIN = 1.1 to 1.5.
The buffered clock crystal output frequency, which can be measured from the
CX25870/1's XTL_BFO output port, should be within 25 ppM = +/- 337 Hz. of 13.5000
MHz. at all times. The high amount of tolerance is necessary so the encoder can
generate sufficient accuracy for the subcarrier frequencies for SECAM, PAL, and NTSC.
If this type of accuracy does not exist when using CXTALIN = 27 pF then CXTALIN should
be increased to 30 pF or 33 pF and the frequency re-measured. Different PCBs exhibit
different amounts of parasitic capacitance so one value for CXTALIN does not
necessarily fit for all designs.
For Bt868/9-designs, CXTALIN and CXTALOUT were recommended to be equal (33 pF).
The 1 MΩ resistor, a requirement of Bt868/9-designs as an external passive between
these 2 pins, is no longer necessary with CX25870/1-designs. If it is present, then this
has no adverse effects on the CX25870/1’s overall video performance.
65
66
N/C
N/C
AGND_DAC
DACD
Whether or not DACD is actually used as a video output within the CX25870/1 design,
this pin must be tied to GND.
For Bt868/9-based designs, this pin was a No Connect and for best performance
should be tied to GND or left open.
Pin 66 for the CX25870/1 is the fourth DAC = DACD.
If DACD is used, connect this output to a video connector. If DACD is not used, leave
this pin no connected for CX25870/1-designs. The circuitry for the low pass filter for
DACD will also need to be added for CX25870/1 designs.
For Bt868/9-based designs, this pin was a No Connect and for best performance
should be tied to GND or left open.
67
N/C
VAA_DACD
This is the power pin for DACD. Whether or not DACD is actually used within the
design, this pin must be tied to VDD=VAA=3.3V for all CX25870/1-designs.
For Bt868/9-based designs, this pin was a No Connect and for best performance
should be tied to GND or left open.
100381B
Conexant
3-13
CONEXANT [ CONEXANT SYSTEMS, INC ]
