Optical disc ICs Preservo amplifier for CD players BA6386K The BA6386K is a preservo amplifier for CD players. By using this paired with a ROHM DSP, a servo and main signal system can be configured with few external components and low power consumption. FApplications CD players FFeatures 1) Internal RF AGC circuits. 2) Internal APC circuit. 3) Internal auto asymmetry circuit. 4) Internal disc defect detector. 5) Internal focus protect function against disc defects. FAbsolute maximum ratings (Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 513 Optical disc ICs Block diagram 514 BA6386K Optical disc ICs BA6386K Pin descriptions 515 Optical disc ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 2.5V) 516 BA6386K Optical disc ICs BA6386K 517 Optical disc ICs Measurement circuit 518 BA6386K Optical disc ICs BA6386K Circuit operation (1) RF amplifier, FOK comparator RFO is shifted downwards from VB by 0.9V. However, the resistance between pins 23 and 24 is set to 20kΩ and if this resistance is changed, use external components to adjust the shift back to 0.9V. Have the feedback resistance 10kΩ or greater. If the DC component of RF rises 0.3V, then FOK becomes high. 519 Optical disc ICs (2) BA6386K FE amplifier and focus search 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. I= 520 VCC*1.4 65k)R11 1 3 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. Optical disc ICs BA6386K (1) LOOP ON timing When FOK turns high, the fall of FE’ is detected and the FOCUS LOOP turns ON. (2) LOOP OFF timing After FOK turns low, the FOCUS LOOP turns OFF after the delay T (s) shown in the figure below. 521 Optical disc ICs (3) APC block and AGC block The initial setting for V1 is 1.2V. When PL-BL (the RF AC amplitude) exceeds a certain value (VAGC), then AGC lowers V1 and suppresses the laser power. The value of VAGC is Iagc 20k, where Iagc is set by the formula given below. Iagc = 1.2 1.4kR18 When R18 = 10kΩ, Iagc = 50µA and VAGC = 1V. When defect turns high, Tr1 turns OFF. 522 BA6386K Optical disc ICs (4) BA6386K DET block When defect is high, the bottom hold (long) charging current is 50µA. The scratch depth (VSC) can be adjusted by changing the resistance at pin 9. VSC = 1.2 R9)200 The peak hold voltage will not go below (GND ) 0.9V) and the bottom hold voltage will not go below (VCC * 0.9V). 4k 523 Optical disc ICs Application example 524 BA6386K Optical disc ICs BA6386K Electrical characteristics curves External dimensions (Units: mm) 525