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| Optical disc ICs Preservo amplifier for CD players BA6387K The BA6387K 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 and 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) 576 Optical disc ICs FBlock diagram BA6387K 577 Optical disc ICs FPin descriptions BA6387K 578 Optical disc ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 2.5V) BA6387K 579 Optical disc ICs BA6387K 580 Optical disc ICs FMeasurement circuit BA6387K 581 Optical disc ICs FCircuit operation (1) RF amplifier, FOK comparator BA6387K 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. 582 Optical disc ICs (2) FE amplifier and focus search BA6387K 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 3 583 Optical disc ICs (1) LOOP ON timing When FOK turns high, the fall of FE' is detected and the FOCUS LOOP turns ON. BA6387K (2) LOOP OFF timing After FOK turns low, the FOCUS LOOP turns OFF after the delay T (s) shown in the figure below. 584 Optical disc ICs (3) APC block and AGC block BA6387K 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 (50A 20k) = 1V. When defect turns high, Tr1 turns OFF. When FON (pin 11) is low, the LD output (pin 6) becomes high. 585 Optical disc ICs (4) DET block BA6387K 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 VSC = 4k The peak hold voltage will not go below (GND ) 0.9V) and the bottom hold voltage will not go below (VCC * 0.9V). 586 Optical disc ICs FApplication example BA6387K 587 Optical disc ICs FElectrical characteristics curves BA6387K FExternal dimensions (Units: mm) 588 |
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