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TDA5155

Pre-amplifier for Hard Disk Drive (HDD) with MR-read/inductive write heads

Philips Electronics 

Philips Semiconductors

Pre-amplifier for Hard Disk Drive (HDD)

with MR-read/inductive write heads

Preliminary specification

TDA5155

8.8 Head unsafe

The HUS pin is an open collector output. Therefore when

the pin is not connected to an external pull-up resistor,

HUS is LOW. HUS pins can be connected together in case

of operation with more than one amplifier. It is used to

detect abnormal or unexpected operation.

Sleep mode: HUS is HIGH, to permit working with more

than one amplifier.

Standby mode: HUS is HIGH, to permit working with

more than one amplifier.

Read mode:

• If in the configuration register d3 = 1, HUS is HIGH

• If in the configuration register d3 = 0, HUS goes LOW

for:

– Selection of a wrong head (H10 to H15)(1)

– Rext pin open, short-circuited to ground or to VCC

(read current too low or too high)

– Low VCC and VCC(WD) conditions. A low supply

voltage detector is placed close to the VCC and

VCC(WD) pins.

Detection of low VCC (main supply): a VCC supply voltage

below 4.0 V ±5% is flagged at the HUS pin. The voltage

detection range is then 4.2 to 3.8 V with an hysteresis of

110 mV ±10%. Detection of low VCC(WD) (write drivers

supply): a fault will be flagged at the HUS pin if VCC(WD)

drops 0.8 V ±10% below VCC. One must be aware that

such a detection is only aimed to warn for a catastrophic

situation. Indeed, VCC(WD) should never be below VCC.

Test mode: HUS is HIGH except when the TAS detector

is ON. If a thermal asperity is detected, HUS goes LOW.

Servo write mode: HUS is LOW.

Write mode:

• If in the configuration register d3 = 1, HUS is LOW

• If in the configuration register d3 = 0, HUS goes HIGH

for:

– Selection of a wrong head (H10 to H15)(1)

– Rext pin open, short-circuited to ground or to VCC

(write current too low or too high)

– Write Data Input frequency too low (WDIx-WDIy)

– Write head Wx, Wy open, Wx or Wy short-circuited to

ground(2)

– Write driver still left biased while not selected

– Low VCC and VCC(WD) conditions (write current inhibit

can be active or inactive).

The same detector is used for read and write mode.

The write current may be inhibited if d2 = 0 in the

configuration register.

The HUS line indicates an unsafe condition as long as the

fault is present, in read mode as well as in write mode.

It indicates again a safe condition only 0.5 µs to 1 µs after

the last fault has disappeared.

(1) Head numbers 0 to 9 are correct, 10 to 15 are signalled as

unsafe.

(2) Switching to write mode makes HUS LOW. After the transient

the HUS detection circuitry is activated. The target for the

head open detection time is 15 ns.

8.9 HUS survey

MODE

Sleep mode

Standby mode

Active mode

HUS

−

−

Read

Write

STATE

−

−

Read mode

A-test mode(1)

TAS mode

Write mode

A-test mode(1)

Servo mode(2)

Notes

1. A-test mode = analog test mode.

2. In servo mode, the performance of the IC is not guaranteed.

DATA BIT D3

0

1

HIGH

HIGH

ACTIVE

HIGH

ACTIVE

ACTIVE

HIGH

LOW

HIGH

HIGH

HIGH

HIGH

ACTIVE

LOW

HIGH

LOW

1997 Apr 08

14

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