LC78620E Datasheet, PDF (13/34 Pages) Sanyo Semicon Device – Compact Disc Player DSP

LC78620E
Note: CLV servo control commands can set the TOFF pin low only in CLV mode. That pin will be at the high level
at all other times. Control of the TOFF pin by microprocessor command is only valid in CLV mode.
• CLV mode
In CLV mode the LC78620E detects the disk speed from the HF signal and provides proper linear speed using
several different control schemes by switching the DSP internal modes. The PWM reference period corresponds to
a frequency of 7.35 kHz. The V/P pin outputs a high level during rough servo and a low level during phase control.
Internal mode
Rough servo (velocity too low)
Rough servo (velocity too high)
Phase control (PCK locked)
CLV⁺
High
Low
PWM
CLV^–
Low
High
PWM
V/P
High
High
Low
• Rough servo gain switching
MSB
LSB
10101000
10101001
Command
DISC 8 SET
DISC 12 SET
RES = low
q
For 8 cm disks, the rough servo mode CLV control gain can be set about 8.5 dB lower than the gain used for 12 cm
disks.
• Phase control gain switching
MSB
LSB
10110001
10110010
10110011
10110000
Command
CLV PHASE COMPARATOR DIVISOR: 1/2
CLV PHASE COMPARATOR DIVISOR: 1/4
CLV PHASE COMPARATOR DIVISOR: 1/8
NO CLV PHASE COMPARATOR DIVISOR USED
RES = low
q
The phase control gain can be changed by changing the divisor used by the dividers in the stage immediately
preceding the phase comparator.
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