Magnetic disk ICs Read / Write amplifier for FDD BH6627FS The BH6627FS is a 4-mode read / zwrite IC designed for floppy disk drives. This IC has an internal active filter that can be set to any of multiple settings according to transfer rate, and internal switches for density and inner track / outer track. Write current can be set to any of multiple settings. Applications Floppy disk drives (1MB, 1.6MB and 2MB drives) Features 1) Internal active filter with four settings that can be selected for multiple Q and f0. 2) Time domain filter with internal switch set 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 535 Magnetic disk ICs Block diagram 536 BH6627FS Magnetic disk ICs BH6627FS Pin descriptions 537 Magnetic disk ICs 538 BH6627FS Magnetic disk ICs BH6627FS 539 Magnetic disk ICs 540 BH6627FS Magnetic disk ICs BH6627FS Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V) 541 Magnetic disk ICs 542 BH6627FS Magnetic disk ICs BH6627FS 543 Magnetic disk ICs BH6627FS Read characteristics Total filter peak frequency setting f0 = a / (RRCC [kΩ] +0.09) [kHz] FILC “H” a = 313 330 376 387 675 844 765 748 “L” 313 330 376 387 627 765 706 754 250 [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 = 758 RRCC [kΩ] +604 [ns] 500 [kbps] : T = 683 RRCC [kΩ] +434 [ns] 500 [kbps] : T = 333 RRCC [kΩ] +388 [ns] Write current switching ratio Write current setting Iwr = 544 24.0 RWCC [kΩ] [mA] Magnetic disk ICs BH6627FS Filter characteristic 545 Magnetic disk ICs BH6627FS 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 546 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 BH6627FS 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 547 Magnetic disk ICs External dimensions (Units: mm) 548 BH6627FS