549
Magnetic disk ICs
Read / Write amplifier for FDD
BH6628AFS
The BH6628AFS is a 4-mode read/write IC designed for floppy disk drives and has an active filter that can be set accord-
ing 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 f0.
2) Time domain filter that is internally switchable ac-
cording to transfer rate.
3) Any of multiple write current settings can be selected,
and inner track/outer track switching is done internal-
ly.
Absolute maximum ratings (Ta = 25C)
Recommended operating conditions (Ta = 25C)
550
Magnetic disk ICs BH6628AFS
Block diagram
551
Magnetic disk ICs BH6628AFS
Pin descriptions and input/output circuits
552
Magnetic disk ICs BH6628AFS
553
Magnetic disk ICs BH6628AFS
554
Magnetic disk ICs BH6628AFS
555
Magnetic disk ICs BH6628AFS
Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V)
556
Magnetic disk ICs BH6628AFS
557
Magnetic disk ICs BH6628AFS
558
Magnetic disk ICs BH6628AFS
Read characteristics
Total filter peak frequency setting
f0 = a/ (RRCC [kΩ] +0.09) [kHz]
FILC “H” “OPEN” “L”
a = 351 318 351 250 [kbps] outer track
380 353 380 250 [kbps] inner track
420 378 420 300 [kbps] outer track
451 416 451 300 [kbps] inner track
729 694 729 500 [kbps] outer track (when F2 = H)
842 807 842 500 [kbps] inner track (when F2 = H)
729 729 729 500 [kbps] outer track (when F2 = L)
780 786 786 500 [kbps] inner track (when F2 = L)
TDF time constant setting
250 [kbps] : T = 796 RRCC [kΩ] +607 [ns]
300 [kbps] : T = 614 RRCC [kΩ] +552 [ns]
500 [kbps] : T = 331 RRCC [kΩ] +448 [ns]
Write current switching ratio
(Write current setting)
Iwr = [mA]
24.0
RWCC [kΩ]
559
Magnetic disk ICs BH6628AFS
Filter characteristic
560
Magnetic disk ICs BH6628AFS
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 differen-
tiated. 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 cur-
rent 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.
561
Magnetic disk ICs BH6628AFS
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 be-
tween digital signals and the head.
Electrical characteristic curves
External dimensions (Units: mm)
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Magnetic disk ICs BH6628AFS
Appendix
Appendix1-Rev1.0
The products listed in this document are designed to be used with ordinary electronic equipment or devices
(such as audio visual equipment, office-automation equipment, communications devices, electrical
appliances and electronic toys).
Should you intend to use these products with equipment or devices which require an extremely high level of
reliability and the malfunction of with would directly endanger human life (such as medical instruments,
transportation equipment, aerospace machinery, nuclear-reactor controllers, fuel controllers and other
safety devices), please be sure to consult with our sales representative in advance.
Notes
No technical content pages of this document may be reproduced in any form or transmitted by any
means without prior permission of ROHM CO.,LTD.
The contents described herein are subject to change without notice. The specifications for the
product described in this document are for reference only. Upon actual use, therefore, please request
that specifications to be separately delivered.
Application circuit diagrams and circuit constants contained herein are shown as examples of standard
use and operation. Please pay careful attention to the peripheral conditions when designing circuits
and deciding upon circuit constants in the set.
Any data, including, but not limited to application circuit diagrams information, described herein
are intended only as illustrations of such devices and not as the specifications for such devices. ROHM
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Products described herein are the objects of controlled goods in Annex 1 (Item 16) of Export Trade Control
Order in Japan.
In case of export from Japan, please confirm if it applies to "objective" criteria or an "informed" (by MITI clause)
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