Out in Front: January 4, 1996

Advanced and next-generation hard-disk drives are using magnetoresistive (MR) heads for high density and speed, exceeding 100 Mbps transfer rates. These heads require preamps with different characteristics from those used with conventional inductive heads. Texas Instruments’ TLS243xx series (for two, four, six, eight, and 10 channels) uses a single-ended input that reduces the number of signal pins required, thus allowing a smaller package than that of a differential-input configuration. You can place the smaller package on the head stack to increase performance with less noise. In addition, the preamp requires no negative supply.

Overall performance of these single-ended preamps, which use differential circuitry internally, is better than all-differential designs. The preamp provides thermal asperity detection, adjusting internal thresholds to accommodate self-heating of the head from head/platter friction and the head’s consequent parameter shifts. The preamps use a current-bias, current-sense architecture and require a 5V supply; idle current is 9 mA. The devices come in TSSOP packages with 30 to 56 contacts, depending on channel count. Input noise is 0.55 nV/[sq root sign]Hz, and -3-dB bandwidth is 140 MHz. The six-channel TLS24306 costs $6 (1000).
-- by Bill Schweber

Texas Instrument Inc, Dallas, TX. (800) 477-8924, ext 4500