BA6387K Datasheet, PDF (8/13 Pages) Rohm – Preservo amplifier for CD players

Optical disc ICs
(2) FE amplifier and focus search
BA6387K
160k
30p
30p
160k
−
+
25
2k
28
2k
26
2k
27
2k
29
31
60k
−
+
60k
−
+
10k
+
−
ON
LOOP ON
OFF
+
−
20k
FOK
ON
OFF
I / 10
I
I
8
1µF
Fig.3 Focus error block
13
11
×3
The voltage for focus search is obtained by the charging
and discharging of the capacitor attached to pin 8. The
charging current is I / 10 and the discharging current is I.
The FEO output amplitude (VSERCH) at this time is
determined by the formula given below.
VSERCH = ± I × 15kΩ × 2 (VB reference)
Moreover, from Fig.3, I can be approximated by the
formula given below.
Set R11 so that I becomes 2µA or greater. Apply biasing
to the focus error signal from pin 29. If no adjustment
occurs, pin 29 = VB .
The timing charts when the focus loop turns ON or OFF
are given on the next page.
I = ^{VCC - 1.4} × ¹
65k + R11
3