Magnetic disk ICs Read / Write amplifier for FDD BH6629BFS The BH6629BFS, a read / write IC designed for floppy disk drives, has a recording system that puts top priority on saddle margin. Offers multi-step switching of write current, while density and inner track / outer track edge are switched internally. Applications Floppy disk drives (1MB and 2MB drives) Features 1) Internal active filter switch. 2) Time domain filter (with internal switching based on transfer rate). 3) Internal switching of write current density and inner track / outer track. Absolute maximum ratings (unless otherwise noted, Ta = 25C) Recommended operating conditions (Ta = 25C) 563 Magnetic disk ICs Block diagram 564 BH6629BFS Magnetic disk ICs BH6629BFS Pin descriptions 565 Magnetic disk ICs 566 BH6629BFS Magnetic disk ICs BH6629BFS 567 Magnetic disk ICs 568 BH6629BFS Magnetic disk ICs BH6629BFS Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V) Supply current Low level voltage detection circuit Recovery time 569 Magnetic disk ICs Preamplifier Preamplifier / L.P.F / differentiator (B.P.F) 570 BH6629BFS Magnetic disk ICs BH6629BFS Comparator and waveform shaping Write circuit Erase output 571 Magnetic disk ICs BH6629BFS Logic input Mode table Total filter peak frequency setting f0 = a / (RRCC [kΩ +0.09) [kHz] a= 391 1M outer track 468 1M inner track 777 2M outer track 786 2M inner track 732 outer track (with OPTION 1), OPTION 2 777 inner track (with OPTION 1) TDF time constant setting 250 [kbps] : T = 939 RRCC [kΩ] +667 [ns] 500 [kbps] : T = 403 RRCC [kΩ] +474 [ns] Write current setting Iwr = 572 24.0 RWCC [kΩ] [mA] Magnetic disk ICs BH6629BFS Filter characteristic 573 Magnetic disk ICs BH6629BFS 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 574 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 BH6629BFS 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 575 Magnetic disk ICs External dimensions (Units: mm) 576 BH6629BFS