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| Communication ICs Read / Write amplifier for FDD BH6625FS The BH6625FS 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. FApplications Floppy disk drives (1MB, 1.6MB and 2MB) FFeatures 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. FAbsolute maximum ratings (unless otherwise noted, Ta = 25_C) FRecommended operating conditions (Ta = 25_C) 373 Communication ICs FBlock diagram BH6625FS 374 Communication ICs FPin descriptions and input / output circuits BH6625FS 375 Communication ICs BH6625FS 376 Communication ICs BH6625FS 377 Communication ICs BH6625FS 378 Communication ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5V) Supply current BH6625FS Low level voltage detection circuit Recovery time 379 Communication ICs Preamplifier BH6625FS Preamplifier / L.P.F / differentiator (B.P.F) 380 Communication ICs Write circuit BH6625FS Erase output Logic input 381 Communication ICs FRead characteristics BH6625FS Total filter peak frequency setting f0 = a / (RRCC [k] +0.09) [kHz] FILC "H" a = 300 339 357 401 677 882 803 748 "OPEN" 353 380 420 451 646 836 702 754 "L" 290 339 345 401 629 732 732 z 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 = 940 300 [kbps] : T = 745 500 [kbps] : T = 377 FWrite current switching ratio RRCC [k] +590 [ns] RRCC [k] +550 [ns] RRCC [k] +476 [ns] Write current setting Iwr = 24.0 RWCC [k] [mA] 382 Communication ICs FFilter characteristic BH6625FS 383 Communication ICs FMeasurement circuit BH6625FS 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. 384 Communication 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. BH6625FS FElectrical characteristic curves 385 Communication ICs BH6625FS FExternal dimensions (Units: mm) 386 |
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