The AD8400/AD8402/AD8403 offer a single, dual or quad channel, 256-bit digitally controlled variable resistance (VR) device. These devices perform the same electronic adjustment function as a potentiometer or variable resistor. The AD8400 contains a single variable resistor in a compact SO-8 package. The AD8402 contains two independent variable resistors in a space saving SO-14 surface mount package. The AD8403 contains four independent variable resistors in 24-lead PDIP, SOIC and TSSOP packages. Each section contains a fixed resistor that determines the wiper contact, and the tap is registered at a point where the fixed resistor value is loaded into the control serial input with a digital code. The resistance between the wiper and the two endpoints is fixed and the resistance changes linearly. The digital code is transferred to the VR latch. Each variable resistor provides a fully programmable resistance value between Terminal A and the wiper or Terminal B and the wiper. "Fixed A to B 1 kW, 10 kW, 50 kW or 100 kW termination resistors have a ±1% channel-to-channel matching tolerance nominal 500 PPM/°C temperature coefficient Unique switching circuit minimizes the Traditional switching is inherently designed with high fault resistors, avoiding any make-before-break or break-off, beforemake operation. Each VR has its own VR latch, holding its programmed resistance value. These VR latches are updated from SPI compatible The serial-to-parallel shift register is loaded from the standard 3-wire serial input digital interface. 10 data bits make up the data word clocked into the serial input register. The first two bits of data word decoding determine the address to be loaded VR latch, last 8 bits are data. Serial register data output pin on the other end allows simple daisy-chaining of multiple VR applications without additional external decode logic. Reset (RS) pin to force wiper The midpoint position of the VR latch is loaded into 80H. The resistance of the SHDN pin forces end-to-end, an open-circuit condition on terminal A shorts the wiper on terminal B, achieving a microwatt power-off state. When SHDN is logic high, the previous latch setting The same resistive wiper settings were used before shutdown. The digital interface is still active at shutdown, so that code changes that will generate new wipers when the device is in the shutdown position. The AD8400 is available in SO-8 surface mount and 8 leaded plastic DIP packages. The AD8402 is available in both surface mount (SO-14) and 14-lead plastic DIP packages, while the AD8403 is available in narrow body 24-lead plastic DIP and 24-lead surface mount packages. AD8402/AD8403 Also available in 1.1mm ultra-thin TSSOP-14/TSSOP-24 packages for PCMCIA applications. All parts are guaranteed to operate over the extended industrial temperature range of -40°C to +85°C.