ISL22446 Datasheet, PDF (11/15 Pages) Intersil Corporation – Quad Digitally Controlled Potentiometer XDCP

ISL22446
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 is recalled and
loaded into the corresponding WRi to set the wiper 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 ISL22446 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 SPI
serial interface as described in the following sections. The
SPI interface register address bits have to be set to 0000b,
0001b, 0010b or 0011b to access the WR of DCP0, DCP1,
DCP2 or DCP3 respectively. The WRi and IVRi can be read
or written to directly using the SPI serial interface as
described in the following sections.
Memory Description
The ISL22446 contains seven non-volatile and five volatile 8-bit
registers. The memory map of ISL22446 is shown in Table 1.
The four non-volatile registers (IVRi) at address 0, 1, 2 and 3,
contain initial wiper value and volatile registers (WRi) contain
current wiper position. In addition, three non-volatile General
Purpose registers from address 4 to address 6 are available.
TABLE 1. MEMORY MAP
ADDRESS
NON-VOLATILE
VOLATILE
8
—
ACR
7
Reserved
TABLE 1. MEMORY MAP (Continued)
ADDRESS
NON-VOLATILE
VOLATILE
6
General Purpose
5
General Purpose
4
General Purpose
Not Available
Not Available
Not Available
3
IVR3
2
IVR2
1
IVR1
0
IVR0
WR3
WR2
WR1
WR0
The non-volatile IVRi and volatile WRi registers are
accessible with the same address.
The Access Control Register (ACR) contains information
and control bits described in Table 2.
The VOL bit (ACR[7]) determines whether the access is to
wiper registers WR or initial value registers IVR.
TABLE 2. ACCESS CONTROL REGISTER (ACR)
BIT # 7 6 5 4
3
2
1
0
Bit Name VOL SHDN WIP 0
0
0
0
0
If VOL bit is 0, the non-volatile IVR register is accessible. If
VOL bit is 1, only the volatile WR is accessible. Note, value
is written to IVR register also is written to the WR. The
default value of this bit is 0.
The SHDN bit (ACR[6]) disables or enables Shutdown mode.
This bit is logically ANDed with SHDN pin. When this bit is 0,
DCP is in Shutdown mode. Default value of SHDN bit is 1.
The WIP bit (ACR[5]) is read only bit. It indicates that non-
volatile write operation is in progress. The WIP bit can be
read repeatedly after a non-volatile write to determine if the
write has been completed. It is impossible to write to the
IVRi, WRi or ACR while WIP bit is 1.
Shutdown Mode
The device can be put in Shutdown mode either by pulling the
SHDN pin to GND or setting the SHDN bit in the ACR register
to 0. The truth table for Shutdown mode is in Table 3.
TABLE 3.
SHDN pin
SHDN bit
Mode
High
1
Normal operation
Low
1
Shutdown
High
0
Shutdown
Low
0
Shutdown
SPI Serial Interface
The ISL22446 supports an SPI serial protocol, mode 0. The
device is accessed via the SDI input and SDO output with data
clocked in on the rising edge of SCK, and clocked out on the
falling edge of SCK. CS must be LOW during communication
with the ISL22446. SCK and CS lines are controlled by the host
or master. The ISL22446 operates only as a slave device.
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FN6181.2
September 9, 2009