Datasheet BH6625FS Datasheet (ROHM)

Magnetic disk 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 .

Applications
Floppy disk drives (1MB, 1.6MB and 2MB)

Features

1) Internal active filter with multiple settings that can be
selected for multiple Q and f

2) Time domain filter that is internally switchable ac­cording to transfer rate.

0.

3) Any of multiple write current settings can be selected,
and inner track / outer track switching is done inter­nally.

Absolute maximum ratings (unless otherwise noted, Ta = 25C)

Recommended operating conditions (Ta = 25C)

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Magnetic disk ICs BH6625FS

Block diagram

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Magnetic disk ICs BH6625FS

Pin descriptions and input / output circuits

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Magnetic disk ICs BH6625FS

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Magnetic disk ICs BH6625FS

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Magnetic disk ICs BH6625FS

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Magnetic disk ICs BH6625FS

Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V)
Supply current

Low level voltage detection circuit

Recovery time

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Magnetic disk ICs BH6625FS

Preamplifier

Preamplifier / L.P.F / differentiator (B.P.F)

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Magnetic disk ICs BH6625FS

Write circuit

Erase output

Logic input

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Magnetic disk ICs BH6625FS

Read characteristics

Total filter peak frequency setting

f

0 = a / (RRCC [kΩ] +0.09) [kHz]

FILC “H” “OPEN” “L”

a = 300 353 290 250 [kbps] outer track

339 380 339 250 [kbps] inner track
357 420 345 300 [kbps] outer track
401 451 401 300 [kbps] inner track
677 646 629 500 [kbps] outer track (when F2 = H)
882 836 732 500 [kbps] inner track (when F2 = H)
803 702 732 500 [kbps] outer track (when F2 = L)
748 754  500 [kbps] inner track (when F2 = L)

TDF time constant setting

250 [kbps] : T = 940  RRCC [kΩ] +590 [ns]
300 [kbps] : T = 745  RRCC [kΩ] +550 [ns]
500 [kbps] : T = 377  RRCC [kΩ] +476 [ns]

Write current switching ratio

Write current setting

Iwr = [mA]

24.0

RWCC [kΩ]

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Magnetic disk ICs BH6625FS

Filter characteristic

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Magnetic disk ICs BH6625FS

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
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.

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Magnetic disk ICs BH6625FS

Operation notes
(1) Use a short pattern for VCC, and a sufficiently wide
AGND and DGND. Keep the impedance between V
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

CC

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Magnetic disk ICs BH6625FS

External dimensions (Units: mm)

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