DP8464B datasheet(6/26 Pages) NSC

6 / 26 page

Pin Definitions

(All pin numbers refer to the 24 pin dual-in-line package)

Name

Function

Power Supply

9VCC

The supply is a12Vg10%

Digital

Digital signals should be referenced

Ground

to this pin

Analog

Analog signals should be referenced

Ground

to this pin

Analog Signals

Amp Ina

These are the differential inputs to

Amp Inb

the Amplifier The output of the read

write head amplifier should be capac-

itively coupled to these pins

Amp Outa

These are the differential outputs of

Amp Outb

the Amplifier These outputs should

be capacitively coupled to the gating

channel filter (if required) and to the

time channel filter

Gate

These are the differential inputs to

Channel

the AGC block and the gating chan-

Inputs

nel These inputs must be capacitive-

ly coupled from the Amp Out

Time

These are the differential inputs to

Channel

the differentiator in the time channel

Inputa

In most applications a filter between

Time

the Amp Out (pins 18 and 19) and

Channel

these inputs is required to band limit

Inputb

the noise and to correct for any

phase distortion introduced by the

read circuitry In all cases this input

must be capacitively coupled to pre-

vent disturbing the DC input level

1Cda

The external differentiator network is

Cdb

connected between these two pins

Set

The DC voltage on this pin sets the

Hysteresis

amount of hysteresis on the differen-

tial comparator Typically this voltage

can be established by a simple resis-

tive divider from the positive supply

4VREF

The AGC circuit adjusts the gain of

the amplifier to make the differential

peak to peak voltage on the Gate

Channel Input equal to four times the

DC voltage on this pin This voltage

can be established by a simple resis-

tive divider from the positive supply

No connection

CAGC

The external capacitor for the AGC is

connected between this pin and Ana-

log Ground

Name

Function

Digital Signals

Set Pulse

An external capacitor to control the

Width

pulse width of the Encoded Data Out

is connected between this pin and

Digital Ground

Read Write

If this pin is low the Pulse Detector is

in the read mode and the chip is ac-

tive When this pin goes high the

pulse detector is forced into a stand-

by mode This is a standard TTL in-

put

Time

This is the TTL output from the bi-di-

Pulse

rectional one shot following the dif-

Out

ferentiator In most applications this

can be connected directly to the

Time Pulse In

Time

This is the TTL input to the clock of

Pulse

the D flip-flop Usually this is con-

nected directly to the Time Pulse Out

Channel

This is the buffered output of the dif-

Alignment

ferential comparator with hysteresis

This is usually used in the initial sys-

tem design and is not used in produc-

tion

Encoded

This is the standard TTL output

Data Out

whose leading edge indicates the

time position of the peaks

Application Information

GENERAL DESCRIPTION

All pin numbers refer to 24 pin dual-in-line package

The DP8464B Disk Pulse Detector utilizes analog and digital

circuitry to detect amplitude peaks of the signal received

from the ReadWrite Amplifier The analog signal from a

disk is a series of pulses the peaks of which correspond to

1’s or flux reversals on the magnetic medium The pulse

detector must accurately determine the time position of

these peaks The peaks are indicated by the positive lead-

ing edge of a TTL compatible output pulse This task is com-

plicated by variable pulse amplitudes depending on the me-

dia type head position head type and readwrite amplifier

circuit gain Additionally as the bit density on the disk in-

creases the amplitude decreases and significant bit interac-

tion occurs resulting in pulse distortion and shifting of the

peaks

The graph in

Figure 1 shows how the pulse amplitude varies

with the number of flux reversals per inch (or recording den-

sity) for a given head disk system The predominant disk

applications are associated with the first two regions on this

graph Regions 1 and 2 Typical waveforms received by the

pulse detector for these regions are shown next to the

graph

DP8464B Datasheet(PDF) 6 Page - National Semiconductor (TI)

DP8464B Datasheet(HTML) 6 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL