ISL23428_15 Datasheet, PDF (14/21 Pages) Intersil Corporation – Dual, 128-Tap, Low Voltage Digitally Controlled Potentiometer (XDCP™)

ISL23428
SERIAL DATA OUTPUT (SDO)
The SDO is a serial data output pin. During a read cycle, the data
bits are shifted out on the falling edge of the serial clock SCK and
will be available to the master on the following rising edge of SCK.
The output type is configured through ACR[1] bit for Push-Pull or
Open Drain operation. Default setting for this pin is Push-Pull. An
external pull-up resistor is required for Open Drain output
operation. When CS is HIGH, the SDO pin is in tri-state (Z) or
high-tri-state (Hi-Z) depends on the selected configuration.
CHIP SELECT (CS)
CS LOW enables the ISL23428, placing it in the active power
mode. A HIGH to LOW transition on CS is required prior to the
start of any operation after power-up. When CS is HIGH, the
ISL23428 is deselected and the SDO pin is at high impedance,
and the device will be in the standby state.
V_LOGIC
Digital power source for the logic control section. It supplies an
internal level translator for 1.2V to 5.5V serial bus operation. Use
the same supply as the I²C logic source.
Principles of Operation
The ISL23428 is an integrated circuit incorporating two DCPs
with its associated registers and an SPI serial interface providing
direct communication between a host and the potentiometer.
The resistor array is 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.
Voltage at any DCP pins, RHi, RLi or RWi, should not exceed V_CC
level at any conditions during power-up and normal operation.
The V_LOGIC pin is the terminal for the logic control digital power
source. It should use the same supply as the SPI logic source
which allows reliable communication with a wide range of
microcontrollers and is independent from the V_CC level. This is
extremely important in systems where the master supply has
lower levels than DCP analog supply.
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
(RHi and RLi pins). The RWi pin of the 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 an 8-bit volatile Wiper Register
(WRi). When the WR of a DCP contains all zeroes
(WRi[7:0] = 00h), its wiper terminal (RWi) is closest to its “Low”
terminal (RLi). When the WRi register of a DCP contains all ones
(WRi[7:0] = 7Fh), its wiper terminal (RWi) is closest to its “High”
terminal (RHi). As the value of the WRi increases from all zeroes
(0) to all ones (127 decimal), the wiper moves monotonically
from the position closest to RLi to the position closest to RHi. At
the same time, the resistance between RWi and RLi increases
monotonically, while the resistance between RHi and RWi
decreases monotonically.
While the ISL23428 is being powered up, both WRi are reset to
40h (64 decimal), which positions RWi at the center between RLi
and RHi.
The WRi can be read or written to directly using the SPI serial
interface, as described in the following sections.
Memory Description
The ISL23428 contains three volatile 8-bit registers: Wiper Register
WR0, Wiper Register WR1, and Access Control Register (ACR).
Memory map of ISL23428 is shown in Table 1. The Wiper Register
WR0 at address 0 contains current wiper position of DCP0; the
Wiper Register WR1 at address 1 contains current wiper position of
DCP1. The Access Control Register (ACR) at address 10h contains
information and control bits described in Table 2.
ADDRESS
(hex)
10
1
0
TABLE 1. MEMORY MAP
VOLATILE
REGISTER NAME
DEFAULT SETTING
(hex)
ACR
40
WR1
40
WR0
40
TABLE 2. ACCESS CONTROL REGISTER (ACR)
BIT # 7
6
5
4
3
2
1
0
NAME/ 0 SHDN 0 0
0
0 SDO 0
VALUE
The SDO bit (ACR[1]) configures type of SDO output pin. The
default value of SDO bit is 0 for Push-Pull output. The SDO pin
can be configured as Open Drain output for some applications. In
this case, an external pull-up resistor is required; reference the
“Serial Interface Specification” on page 7.
Shutdown Function
The SHDN bit (ACR[6]) disables or enables shutdown mode for all
DCP channels simultaneously. When this bit is 0, i.e., each DCP is
forced to end-to-end open circuit and each RW shorted to RL
through a 2kΩ serial resistor, as shown in Figure 25. Default value
of the SHDN bit is 1.
RH
RW
2kΩ
RL
FIGURE 25. DCP CONNECTION IN SHUTDOWN MODE
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FN7904.2
September 23, 2015