CXA1720Q Datasheet, PDF (15/26 Pages) Sony Corporation – Read/Write Amplifier (with Built-in Filters) for FDDs

CXA1720Q
Comparator
The comparator detects the crosspoint of the filter differential output.
Time domain filter
The time domain filter converts the comparator output to Read data.
This filter is equipped with two monostable multivibrators. Monostable multivibrator No. 1 eliminates
unnecessary pulses, and monostable multivibrator No. 2 determines the pulse width of Read data.
The monostable multivibrator No. 1 pulse width TA is determined by the resistor RA between Pin 12 and
A.GND. TA can be switched as follows by the setting of Pin 9:
HIGH DENSITY = “H” TA LOW = 84RA + 180 (nS) RA (kΩ)
HIGH DENSITY = “L” TA HIGH = 42RA + 110 (nS)
The pulse width for monostable multivibrator No. 2 is fixed at 400 ns.
(2) Write System
Write data input through Pin 2 is frequency-divided by the T flip-flop and generates the head recording
current. The recording current can be switched by the setting of Pin 9.
The Write current Iw is set by the resistor RW connected between Pin 25 and VCC and between Pin 27 and
VCC.
IW = 11.6/RW (mA)
RW (kΩ)
Furthermore, the Write current compensation IWC is set by the resistor RWC connected between Pin 25 and Pin
26, and between Pin 27 and Pin 28.
IWC = 10.8/RWC (mA) RWC (kΩ)
(3) Erase System
Pins 30 and 31 are open collector outputs; the Erase current is set by the resistance between these pins
and the Erase head.
(4) Power ON/OFF Detection System
The power ON/OFF detection system detects a reduced voltage.
When VCC is below the stipulated voltage, the Write system and Erase system cease operation, disabling
the Write and Erase functions
Notes on Operation
• Select the voltage gain so that the pre-amplifier output amplitude is 1 Vp-p or less.
If the pre-amplifier output amplitude exceeds 1 Vp-p, the filter output waveform becomes distorted.
• Observe the following points when mounting this IC.
• Connect a VCC decoupling capacitor of approximately 0.1 µF close to the IC.
• The ground should be as large as possible.
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