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ISL22346WFRT20Z Fiches technique(PDF) 11 Page - Intersil Corporation |
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ISL22346WFRT20Z Fiches technique(HTML) 11 Page - Intersil Corporation |
11 / 16 page 11 FN6177.2 September 3, 2009 Pin Descriptions Potentiometers Pins RHI AND RLI (i = 0, 1, 2 OR 3) The high (RHi) and low (RLi) terminals of the ISL22346 are equivalent to the fixed terminals of a mechanical potentiometer. RHi and RLi are referenced to the relative position of the wiper and not the voltage potential on the terminals. With WRi set to 127 decimal, the wiper will be closest to RHi, and with the WRi set to 0, the wiper is closest to RLi. RWI (i = 0, 1, 2 OR 3) RWi is the wiper terminal and is equivalent to the movable terminal of a mechanical potentiometer. The position of the wiper within the array is determined by the WRi register. SHDN The SHDN pin forces the resistor to end-to-end open circuit condition on RHi and shorts RWi to RLi. When SHDN is returned to logic high, the previous latch settings put RWi at the same resistance setting prior to shutdown. This pin is logically ANDed with SHDN bit in ACR register. I2C interface is still available in shutdown mode and all registers are accessible. This pin must remain HIGH for normal operation. Bus Interface Pins SERIAL DATA INPUT/OUTPUT (SDA) The SDA is a bidirectional serial data input/output pin for I2C interface. It receives device address, operation code, wiper address and data from an I2C external master device at the rising edge of the serial clock SCL, and it shifts out data after each falling edge of the serial clock. SDA requires an external pull-up resistor, since it is an open drain input/output. SERIAL CLOCK (SCL) This is the serial clock input of the I2C serial interface. SCL requires an external pull-up resistor, since it is an open drain input. DEVICE ADDRESS (A2 - A0) The address inputs are used to set the least significant 3 bits of the 7-bit I2C interface slave address. A match in the slave address serial data stream must match with the Address input pins in order to initiate communication with the ISL22346. A maximum of 8 ISL22346 devices may occupy the I2C serial bus. Principles of Operation The ISL22346 is an integrated circuit incorporating four DCPs with their associated registers, non-volatile memory and an I2C serial interface providing direct communication between a host and the potentiometers and memory. The resistor arrays are comprised of individual resistors connected in series. At either end of the array and between each resistor is an electronic switch that transfers the potential at that point to the wiper. The electronic switches on the device operate in a “make before break” mode when the wiper changes tap positions. When the device is powered down, the last value stored in IVRi will be maintained in the non-volatile memory. When power is restored, the contents of the IVRi are recalled and loaded into the corresponding WRi to set the wipers to the initial value. DCP Description Each DCP is implemented with a combination of resistor elements and CMOS switches. The physical ends of each DCP are equivalent to the fixed terminals of a mechanical potentiometer (RH and RL pins). The RW pin of each DCP is connected to intermediate nodes, and is equivalent to the wiper terminal of a mechanical potentiometer. The position of the wiper terminal within the DCP is controlled by volatile Wiper Register (WR). Each DCP has its own WR. When the WR of a DCP contains all zeroes (WR[6:0]= 00h), its wiper terminal (RW) is closest to its “Low” terminal (RL). When the WR register of a DCP contains all ones (WR[6:0]= 7Fh), its wiper terminal (RW) is closest to its “High” terminal (RH). As the value of the WR increases from all zeroes (0) to all ones (127 decimal), the wiper moves monotonically from the position closest to RL to the closest to RH. At the same time, the resistance between RW and RL increases monotonically, while the resistance between RH and RW decreases monotonically. While the ISL22346 is being powered up, all four WRs are reset to 40h (64 decimal), which locates RW roughly at the center between RL and RH. After the power supply voltage becomes large enough for reliable non-volatile memory reading, all WRs will be reload with the value stored in corresponding non-volatile Initial Value Registers (IVRs). The WRs can be read or written to directly using the I2C serial interface as described in the following sections. The I2C interface Address Byte has to be set to 00h, 01h, 02h or 03h to access the WR of DCP0, DCP1, DCP2 or DCP3 respectively. RL RW RH FIGURE 15. DCP CONNECTION IN SHUTDOWN MODE ISL22346 |
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