VM310

The VM310 has the following features including Enhanced System Write to Read Recovery Time;Power-Up/Power-Down Write Protection;Plug Compatible to the VTC VM117;Operates on +5V and +12V Power Supplies;Write-Unsafe Detection Circuitry;Programmable Write-Current Source;TTL-Compatible Control Lines;Low input Noise of 1 .4n V/ yHZ  maximum;For Use With Center-Tapped Ferrite Heads;Optional Internal Head Damping Resistors;Available in 2, 4, or 6 Channels;Mirror Image Pinout Option Available.

The VM310 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. After the fault condition is corrected, it takes two negative transitions on WDI to clear the WUS line. To further protect accidental writing to the disk, a voltage fault detection circuit ensures no write currant during power loss or power sequencing. An enhanced write to read recovery time is achieved by maintaining a constant common mode level on the RDX, RDY outputs between write and read modes.Write mode power dissipation may be minimized by connecting a resistor (RCT) between VDD2 and VDD1. The optimum value for RCT is 120x40/Iw (1w in mA). At write currents below 15mA, the read mode dissipation is higher than write mode and need not be used. In this case VDD2 is connected to VDD1.

In the read mode the VM310 circuit operates as a low-noise differential amplifier. The write-current source of VM310 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 and should be AC coupled to the load.  Write current is deactivated for both the read and idle mode so that external gating is not required.In the idle mode (CS=high level) both the read amp and write driver are disabled and the devices power dissipation is minimal. The internal write current reference is disabled and the RDX, RDY outputs are in a high impedance state.  Hence,for multiply chip usage. The RDX, RDY outputs maybe wire OR'ed, and a common write current resistor (RWC) may be used to set the write current.