1998 July 30
Philips Semiconductors Objective Specification, Revision 2.2
Pre-Amplifier for Hard Disk Drive with
MR-Read / Inductive Write Heads
TDA5360
12
10 BIASING OF THE MR ELEMENT
This preamplifier has been designed for SAL and GMR elements. Programming bit GMR in Reg. 01 select either a SAL
range (LOW) or a GMR range (HIGH).
By programming bit PORI in Reg. 01, the user can program either a constant current bias (LOW) or a constant power
bias (HIGH) for the MR element. The value of the current/power is programmed on 5 bits via Reg. 02.
If bit PORI in Reg. 01 is HIGH, a constant power bias is maintained accross the MR element.
The power is defined as :
Pw = R
MR
* I
MR
2
, where Pw is constant over temperature and process.
In power bias mode, two power ranges are possible :
For SAL heads 1.5mW to 9.25 mW in steps of 0.25mW
For GMR heads 375uW to 2.3 mW in steps of 0.0625mW
Note : whatever Power programmation is used, the I
MR
current flowing into the MR element will be within the min-
max range given below.
If bit PORI in Reg.01 is LOW, then the biasing scheme shall revert to constant current instead of constant power.
I
MR
is then constant over temperature and process.
In current bias mode, two current ranges are possible :
For SAL heads : 4 to 10.2 mA in steps of 0.2 mA
For GMR heads : 3 to 6.1 mA in steps of 0.1 mA
Note : In GMR mode, I
MR
current is guaranted up to 5.1mA
6.1mA can be reached under certain supplies/Rmr conditions.
10.1 MR Head Resistance and Temperature Measurement
By programming RANGE0,RANGE1 bits in Reg. 08, the user can select either a Rmr measurement or a Temperature
measurement (junction temperature).
Setting DIGON bit HIGH launch a digitazation
The settling time of the digitization operation is less than TBD ยตs.
A 5 bit code is then available in Reg. 08, as long as DIGON stays HIGH,
Setting DIGON bit LOW, reset the 5 bit code.
In case of Rmr measurement, the user have access to two Rmr range by programming RANGE0 and RANGE1 bits.
In case of Temperature too high condition (T > 140
o
C), during a Temperature measurement, a Fault is triggered on FLT
line and a error code is available in Reg. 07.
