Magnetic disk ICs Read / Write amplifier for FDD BH6628AFS The BH6628AFS is a 4-mode read / write IC designed for floppy disk drives and has an active filter that can be set according to transfer rate. Any of multiple write current settings can be selected, and inner track / outer track switching is done internally. Applications Floppy disk drives (1MB, 1.6MB and 2MB) Features 1) Internal active filter with multiple settings that can be selected for multiple Q and f0. 2) Time domain filter that is internally switchable according to transfer rate. 3) Any of multiple write current settings can be selected, and inner track/outer track switching is done internally. Absolute maximum ratings (Ta = 25C) Recommended operating conditions (Ta = 25C) 549 Magnetic disk ICs Block diagram 550 BH6628AFS Magnetic disk ICs BH6628AFS Pin descriptions and input/output circuits 551 Magnetic disk ICs 552 BH6628AFS Magnetic disk ICs BH6628AFS 553 Magnetic disk ICs 554 BH6628AFS Magnetic disk ICs BH6628AFS Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V) 555 Magnetic disk ICs 556 BH6628AFS Magnetic disk ICs BH6628AFS 557 Magnetic disk ICs BH6628AFS Read characteristics Total filter peak frequency setting f0 = a / (RRCC [kΩ] +0.09) [kHz] FILC “H” a = 351 380 420 451 729 842 729 780 “OPEN” 318 353 378 416 694 807 729 786 “L” 351 380 420 451 729 842 729 786 250 [kbps] outer track 250 [kbps] inner track 300 [kbps] outer track 300 [kbps] inner track 500 [kbps] outer track (when F2 = H) 500 [kbps] inner track (when F2 = H) 500 [kbps] outer track (when F2 = L) 500 [kbps] inner track (when F2 = L) TDF time constant setting 250 [kbps] : T = 796 RRCC [kΩ] +607 [ns] 300 [kbps] : T = 614 RRCC [kΩ] +552 [ns] 500 [kbps] : T = 331 RRCC [kΩ] +448 [ns] Write current switching ratio (Write current setting) Iwr = 558 24.0 RWCC [kΩ] [mA] Magnetic disk ICs BH6628AFS Filter characteristic 559 Magnetic disk ICs BH6628AFS Measurement circuit Circuit operation (1) Read The input signal from the head coils from each side of the disc is amplified by the preamplifier and then differentiated. The filter time constant can be set externally. After differentiation, the differential output is input to the comparator. The time domain filter detects zero cross, and the output is converted to read data. The monostable multivibrator width can be set externally, while the read data pulse width is a constant 400ns. (2) Write Input write data are converted to toggle movements by 560 the internal flip-flops, operating the write driver. The write driver current is supplied by the write current generator, but the externally set current can be controlled according to density and by selecting inner track / outer track. (3) Erase An open collector output pin is used, and the erase current is set with a resistor between it and the head. (4) Power supply When the low level voltage detector detects a drop in the supply voltage, writing and erasing are prohibited. Magnetic disk ICs BH6628AFS Operation notes (1) Use a short pattern for VCC, and a sufficiently wide AGND and DGND. Keep the impedance between VCC and GND low by inserting a bypass capacitor. (2) Use a pattern that will minimize interference between digital signals and the head. Electrical characteristic curves 561 Magnetic disk ICs External dimensions (Units: mm) 562 BH6628AFS