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AS1507

Data Sheet - D e t a i l e d D e s c r i p t i o n

8 Detailed Description

The AS1507 contains two resistor arrays with 255 resistive elements each (tap points), and has a total end-to-end

resistance of 10, 50, or 100k

Ω (see Ordering Information on page 16).

The device provides high, low, and wiper terminals for a standard voltage-divider configuration. Pins HIGH, LOW, and

A 3-wire, SPI-compatible serial interface controls movement of the wiper among the 256 tap points. The EEPROM

stores the wiper position and recalls the stored wiper position upon power-up. The EEPROM typically holds wiper data

for 150 years and up to 10M wiper store cycles.

Analog Circuit

The 256 tap points are accessible to the wiper along the resistor string between pins HIGH and LOW (similar to the

end terminals of a mechanical potentiometer). The wiper tap point is selected by programming 8 data bits and a control

byte via the 3-wire serial interface (see Programming the Device on page 10).

Note: Integrated power-on reset circuitry loads the wiper position from the EEPROM at power-up.

Digital Interface

The AS1507 uses an SPI-compatible 3-wire interface for command settings of the device consisting of two input sig-

nals (chip-select - CSN, and data clock - SCLK) and one bi-directional data pin (SDIO). Driving CSN low enables serial

interface and the command/data are passed into the device synchronously by each SCLK rising edge.

There are 16-bit commands for write data into the wiper register or the non-volatile memory, and 8-bit commands for

transferring data between wiper register and non-volatile memory and to read the data stored in the wiper register or

non-volatile memory. The 8-bit commands can be implemented in 16-bit command structure alternatively. In this case

the first 8 bits shifted through the SPI interface are not significant. The data byte passed at writing commands repre-

sents the position of the wiper.

After loading the 8- or 16-bit command while CSN is low, the loaded command is executed at the next rising edge of

CSN, simultaneously the serial interface is disabled. The CSN signal must be low during the whole serial input stream

through the SPI, otherwise data on the SPI interface are corrupted.

Note: If the data-in stream does not exactly contain 8 or 16 digits, no command is executed at the rising edge of

CSN.

Figure 20. Serial Data Timing

Standby Mode

Low-power standby mode is enabled at CSN high. After a read access standby mode is entered 2 cycles of SCLK

leakage power dissipation of the device.

This power dissipation is defined with 0.1uA (typ) at 25ºC.

...

...

...

CSN

SCLK

SDIO