ADI AD8402ARUZ100

The AD8400/AD8402/AD8403 are single-channel/dual-channel/quad-channel, 256-position, digitally controlled variable resistance (VR) devices that perform the same electronic adjustment function as mechanical potentiometers or rheostats. The AD8400 contains one VR in a compact SOIC-8 package. The AD8402 contains two independent VRs in a space-saving SOIC-14 surface-mount package. The AD8403 contains four independent VRs available in 24-pin PDIP, SOIC, and TSSOP packages. Each device contains a fixed resistor with a wiper contact that taps the fixed resistance value at a position determined by the digital code loaded into the control serial input register. The resistance between the wiper and either end of the fixed resistor varies linearly with the digital code transferred to the VR latch. Between the A terminal and wiper, or the B terminal and wiper, each VR provides a fully programmable resistance. The channel-to-channel matching tolerance of the A-to-B end-to-end resistance (1 kΩ, 10 kΩ, 50 kΩ, or 100 kΩ) is ±1%, with a nominal temperature coefficient of 500 ppm/°C. A unique switching circuit minimizes the large glitches inherent in conventional switched-resistor designs, eliminating any make-before-break or break-before-make switching.

Each VR has its own VR latch that stores its programmed resistance value. These VR latches are updated by an SPI-compatible serial-to-parallel shift register that is loaded from a standard 3-wire serial digital interface. A 10-bit data word is transferred to the serial input register. This data word is decoded such that the first 2 bits determine the VR latch address to be loaded, and the remaining 8 bits are data. Using the serial data output pin at the opposite end of the shift register, multiple VRs can be daisy-chained in a simple configuration without additional external decoding logic.

The reset (RS) pin forces the wiper to the midscale position by loading 80H into the VR latches. The SHDN pin forces the A-terminal resistance to an end-to-end open circuit and shorts the wiper to the B terminal, achieving a shutdown state with milliwatt-level power consumption. When SHDN returns to a logic high, the previous latch settings restore the wiper to its pre-shutdown resistance value. The digital interface remains active during shutdown to allow code changes, so that when the device exits shutdown, the wiper will be at the new position.

The AD8400 is available in an SOIC-8 surface-mount package. The AD8402 is available in surface-mount (SOIC-14) and 14-pin PDIP packages. The AD8403 is available in narrow-body 24-pin PDIP and 24-pin surface-mount packages. The AD8402/AD8403 are also available in 1.1 mm thin TSSOP-14/TSSOP-24 packages for PCMCIA applications. All devices are guaranteed over the extended industrial temperature range of −40°C to +125°C.

• 256-position variable resistor
• Replaces 1, 2, or 4 potentiometers
• 1 kΩ, 70 kΩ, 50 kΩ, 100 kΩ
• Power consumption (shutdown mode): less than 0.5 μA
• 3-wire SPI-compatible serial data input
• Data update load rate: 10 MHz
• 2.7 V to 5.5 V single-supply operation
• Automotive-qualified

• Mechanical potentiometer replacement
• Programmable filters, delays, time constants
• Volume control, panning
• Line impedance matching
• Power supply adjustment