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AD5293
Rev. D | Page 19 of 24
RESET
A low-to-high transition of the hardware RESET pin loads the
RDAC register with midscale. The AD5293 can also be reset
through software by executing Command 3 (see
).
The control register is restored with default bits (see
).
RESISTOR PERFORMANCE MODE
This mode activates a new, patented 1% end-to-end resistor
tolerance that ensures a ±1% resistor tolerance on each code,
that is, code = half scale, RWB =10 kΩ ± 100 Ω. See Table 2 and Table 4 to verify which codes achieve ±1% resistor tolerance.
The resistor performance mode is activated by programming
SDO PIN AND DAISY-CHAIN OPERATION
The serial data output pin (SDO) serves two purposes: it can
be used to read the contents of the wiper setting and control
register using Command 2, and Command 5, respectively (see
Table 11) or the SDO pin can be used in daisy-chain mode.
Data is clocked out of SDO on the rising edge of SCLK. The
SDO pin contains an open-drain N-channel FET that requires
a pull-up resistor if this pin is used. To place the pin in high
impedance and minimize the power dissipation when the pin
is used, the 0x8001 data word followed by Command 0 should
be sent to the part.
Table 10 provides a sample listing for the
sequence of the serial data input (DIN). Daisy chaining mini-
mizes the number of port pins required from the controlling IC.
As shown in
Figure 45, users need to tie the SDO pin of one
package to the DIN pin of the next package. Users may need to
increase the clock period, because the pull-up resistor and the
capacitive loading at the SDO-to-DIN interface may require
additional time delay between subsequent devices.
When two AD5293s are daisy-chained, 32 bits of data are required.
The first 16 bits go to U2, and the second 16 bits go to U1. The
SYNC pin should be held low until all 32 bits are clocked into
their respective serial registers. The SYNC pin is then pulled
high to complete the operation.
Keep the SYNC pin low until all 32 bits are clocked into their
respective serial registers. The SYNC pin is then pulled high to
complete the operation.
DIN
SDO
SCLK
RP
2.2k
DIN
SDO
U1
U2
AD5293
SYNC
VLOGIC
MICRO-
CONTROLLER
SCLK
SS
MOSI
SYNC
07
67
5-
03
9
Figure 45. Daisy-Chain Configuration Using SDO
Table 10. Minimize Power Dissipation at the SDO Pin
DIN
Action
0xXXXX
Last user command sent to the digipot
0x8001
0xXXXX
Prepares the SDO pin to be placed in high impedance mode
0x0000
High impedance
The SDO pin is placed in high impedance
1 X = don’t care.
Table 11. Command Operation Truth Table
Command Bits[B13:B10]
Command
C3
C2
C1
C0
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
Operation
0
X
NOP command. Do nothing.
1
0
1
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
Write contents of serial register data
to RDAC.
2
0
1
0
X
Read RDAC wiper setting from SDO
output in the next frame.
3
0
1
0
X
Reset. Refresh RDAC with midscale code.
4
0
1
0
X
D2
D1
X
Write contents of serial register data
to control register.
5
0
1
X
Read control register from SDO output
in the next frame.
6
1
0
X
D0
Software power-down.
D0 = 0 (normal mode).
D0 = 1 (device placed in shutdown
mode).
1 X = don’t care.
Table 12. Control Register Bit Map
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
1 X = don’t care.