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| 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 FBlock diagram BA6386K 514 Optical disc ICs FPin descriptions BA6386K 515 Optical disc ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 2.5V) BA6386K 516 Optical disc ICs BA6386K 517 Optical disc ICs FMeasurement circuit BA6386K 518 Optical disc ICs FCircuit operation (1) RF amplifier, FOK comparator BA6386K RFO is shifted downwards from VB by 0.9V. However, the resistance between pins 23 and 24 is set to 20k and if this resistance is changed, use external components to adjust the shift back to 0.9V. Have the feedback resistance 10k or greater. If the DC component of RF rises 0.3V, then FOK becomes high. 519 Optical disc ICs (2) FE amplifier and focus search BA6386K 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 15k 2 (VB reference) Set R11 so that I becomes 2A 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. Moreover, from Fig. 3, I can be approximated by the formula given below. I= VCC*1.4 65k)R11 1 3 520 Optical disc ICs (1) LOOP ON timing When FOK turns high, the fall of FE' is detected and the FOCUS LOOP turns ON. BA6386K (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 BA6386K 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 1.4k)R18 When R18 = 10k, Iagc = 50A and VAGC = 1V. When defect turns high, Tr1 turns OFF. 522 Optical disc ICs (4) DET block BA6386K When defect is high, the bottom hold (long) charging current is 50A. The scratch depth (VSC) can be adjusted by changing the resistance at pin 9. 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). VSC = 4k 523 Optical disc ICs FApplication example BA6386K 524 Optical disc ICs FElectrical characteristics curves BA6386K FExternal dimensions (Units: mm) 525 |
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