VM311

The VM311 has the following features including Enhanced System Write to Read Recovery Time;Power-Up/Power-Down Write Protection;Operates on +5V and +12V Power Supplies;Write-Unsafe Detection Circuitry;Programmable Write-Current Source;For Use With Center-Tapped Ferrite or MIG Heads;Optional Internal Head Damping Resistors;Available in 4, 6 or 8 Channels;Mirror Image Pinout Option Available.

The VM311 is a bipolar, monolithic read/write preamp circuit, designed for use with center-tapped ferrite or MIG 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 faun crondition is corrected, ft takes two negative transitions on WDI to clear the WUS line. To further protect accidental writing to the disk, a voRage fault detection circuit ensures no write current 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 (Iw 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 VM311 circuit operates as a low-noise differential amplifier. The write-current source of VM311 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 Goth the read and idle mode so that external gating is not required.Read-to-Write Recovery should be enhanced when doing a DC erase. Layout of the chip minimizes thermal effects on the read amp for improved write-to-read recovery.