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| Magnetic disk ICs Read / Write amplifier for FDD BH6626FS The BH6626FS is a read / write IC designed for floppy disk drives and has an internal active filter for memory systems in which saddle margins are important. Any of multiple write current settings can be selected, and both density switching and inner track / outer track switching are done internally. FApplications Floppy disc drives (1MB and 2MB) FFeatures 1) Active filter switched internally. 2) Time domain filter with internal switch set according to transfer rate. 3) Density switching and inner track / outer track switching are done internally. FAbsolute maximum ratings (unless otherwise noted, Ta = 25_C) FRecommended operating conditions 522 Magnetic disk ICs FBlock diagram BH6626FS 523 Magnetic disk ICs FPin descriptions and Input / output circuits BH6626FS 524 Magnetic disk ICs BH6626FS 525 Magnetic disk ICs BH6626FS 526 Magnetic disk ICs BH6626FS FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5V) Supply current 527 Magnetic disk ICs Low level voltage detection circuit BH6626FS Recovery time Preamplifier 528 Magnetic disk ICs Preamplifier / L.P.F / differentiator (B.P.F) BH6626FS Comparator and waveform shaping Write circuit 529 Magnetic disk ICs Erase output BH6626FS Logic input FMode table Total filter peak frequency setting f0 = a / (RRCC [k] +0.09) [kHz] a= 412 1M outer track 439 1M inner track 790 2M outer track 867 2M inner track 732 outer track(with OPTION 1), OPTION 2 836 inner track (with OPTION 1) TDF time constant setting 250 [kbps] : T = 939 500 [kbps] : T = 403 Write current setting Iwr = RRCC [k] +667 [ns] RRCC [k] +474 [ns] 24.0 RWCC [k] [mA] 530 Magnetic disk ICs FFilter characteristic BH6626FS 531 Magnetic disk ICs FMeasurement circuit BH6626FS FCircuit 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 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. 532 Magnetic disk ICs FOperation 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. BH6626FS FElectrical characteristic curves 533 Magnetic disk ICs BH6626FS FExternal dimensions (Units: mm) 534 |
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