VM118

The VM118 has the following features including Operates on +5V and +12V Power Supplies;Programmable Write-Current Source;TTL-Compatible Control Lines;Wrtte-Unsafe Detection Cirouitry;Low Input Noise;For Use With Center-Tapped Thin-Film Heads;Power-Up/Power-Down Write Protection;Optional Internal Head Damping Resistors;Available in 2, 4 and 6 Channels.

The VM118 is a bipolar, monolRhic read/write preamp circufl designed for use with cellar-tapped thin-lilm 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.The VM118NM118R operates as a writecurrent switch in write mode and as a low-noise differential amplifier in the read mode. Channel selection Is controlled by HS0,HSi 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.In the write mode, the VM118 operates as a write-current switch. Wrke current is supplied by an internal current source. The magnkude of the write current is determined by an external resistor connected between WC and ground. The head current is swkched between the X and Y side of a selected head by falling transitions on WDI (write data input). When swkching to the wrke mode from the read mode, the write data flip-flop Is inkialized to pass head current through the X side of the head.

In the read mode, the VM118 circuit operates as a low-noise differential amplifier. The write current source is fumed 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.