AD7376

The AD7376 provides a single channel, 128-position digitallycontrolled variable resistor (VR) device. This device performs the same electronic adjustment function as a potentiometer or variable resistor. These products were optimized for instrument and test equipment applications where a combination of high voltage with a choice between bandwidth or power dissipation are available as a result of the wide selection of end-to-end terminal resistance values. The AD7376 contains a fixed resistor with a wipercontact that taps the fixed resistor value at a point determined by a digital code loaded into the SPI-compatible serial-input register. The resistance between the wiper and either endpoint of the fixed resistor varies linearly with respect to the digital code transferred into the VR latch. The variable resistor offers a completely programmable value of resistance between the A terminal and the wiper or the B terminal and the wiper. The fixed A to B terminal resistance of 10 kW, 50 kW, 100 kW or 1 MW has a nominal temperature coefficient of 300 ppm/°C.

The VR has its own VR latch which holds its programmed resistance value. The VR latch is updated from an internal serial-toparallel shift register which is loaded from a standard 3-wire
serial-input digital interface. Seven data bits make up the data word clocked into the serial data input register (SDI). Only the last seven bits of the data word loaded are transferred into the 7-bitVRlatchwhen the CS strobe is returned to logic high. A serial data output pin (SDO) at the opposite end of the serial register allows simple daisy-chaining in multipleVRapplications
without additional external decoding logic. The reset (RS ) pin forces the wiper to the midscale position by loading 40H into the VR latch. The SHDN pin forces the resistor to an end-to-end open circuit condition on the A terminal and shorts the wiper to the B terminal, achieving a microwatt power shutdown state. When shutdown is returned to logic high, the previous latch settings put the wiper in the same resistance setting prior to shutdown as long as power to VDD is not removed. The digital interface is still active in shutdown so that code changes can be made that will produce a new wiper position when the device is taken out of shutdown. The AD7376 is available in both surface mount (SOL-16) andthe 14-lead plastic DIP package. For ultracompact solutions selected models are available in the thin TSSOP package. All parts are guaranteed to operate over the extended industrial temperature range of 40°C to +85°C. For operation at lower supply voltages (+3 V to +5 V), see the AD8400/AD8402/AD8403 products.