VM217

The VM217 has the following features including Power Up/Down Protection Circuitry;Operates On +5V and +12V Power Supplies;Programmable Write-Current Source;TTL-Compatible Control Lines;Write Unsafe Detection Circuitry;Low Input Noise;For Use With Center-Tapped Ferrite Heads;Optional Internal Head Damping Resistors;Available In 6 or 8 Channels.

The VM217 is a bipolar, monolithic read/write preamp circuit, designed for use with center-tapped ferrite recording heads. The circuit provides a low-noise read data path for signals from the disk in the read mode and provides write-current control for data written on the disk in the write mode.In the write mode, the VM217 operates as a write current switch.  Write current is supplied by an internal current source. The magnitude of the write current is determined by an external resistor, R WC,connected between WC and ground. The head current is switched between the X and Y side of a selected head by falling transitions on WDI (write data input). When switching to the write mode from the read mode, the write data flip-flop is initialized to pass head current through the X side of the head.

In the read mode the circuit operates as a low-noise differential amplifier. The write current source is turned off and the write data flip-flop is set. The selected head provides a differential input. The RDX and RDY pins provide differential emitter follower outputs which are in phase with the X and Y inputs.Write current is deactivated for both the read and the idle mode so that external gating is not required.The VM217 operates as a write-current switch in the write mode and as a low-noise differential amplifier in the read mode. Channel selection is controlled by HSO, HS1 and HS2 lines and mode select is controlled by the CS and R/W select lines.  Both CS and R/W have internal pull-up resistors to prevent accidental write conditions. Unsafe write conditions are indicated by the WUS line. The VM217 also incorporates power up/down protection circuitry to prevent write-current spikes in the event of sudden power up or power down conditions.