ROHM BH6627FS

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
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Magnetic disk ICs
Block diagram
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BH6627FS
Magnetic disk ICs
BH6627FS
Pin descriptions
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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
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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