Datasheet

Data Sheet AD5235
Rev. F | Page 23 of 32
Because the AD5235 can also be supplied by dual supplies, the
general equation defining the output voltage at V
W
with respect
to ground for any given input voltages applied to Terminal A
and Terminal B is
B
AB
W
VV
D
DV +×=
1024
)(
(3)
Equation 3 assumes that V
W
is buffered so that the effect of wiper
resistance is minimized. Operation of the digital potentiometer in
divider mode results in more accurate operation over temperature.
Here, the output voltage is dependent on the ratio of the internal
resistors and not the absolute value; therefore, the drift improves
to 15 ppm/°C. There is no voltage polarity restriction between
Terminal A, Terminal B, and Terminal W as long as the
terminal voltage (V
TERM
) stays within V
SS
< V
TERM
< V
DD
.
PROGRAMMING EXAMPLES
The following programming examples illustrate a typical sequence
of events for various features of the AD5235. See Table 7 for the
instructions and data-word format. The instruction numbers,
addresses, and data appearing at the SDI and SDO pins are in
hexadecimal format.
Table 14. Scratchpad Programming
SDI SDO Action
0xB00100 0xXXXXXX Writes Data 0x100 into RDAC1 register,
Wiper W1 moves to 1/4 full-scale
position.
0xB10200 0xB00100 Loads Data 0x200 into RDAC2 register,
Wiper W2 moves to 1/2 full-scale
position.
Table 15. Incrementing RDAC Followed by Storing the
Wiper Setting to EEMEM
SDI SDO Action
0xB00100 0xXXXXXX Writes Data 0x100 into RDAC1
register, Wiper W1 moves to 1/4 full-
scale position.
0xE0XXXX 0xB00100 Increments RDAC1 register by one to
0x101.
0xE0XXXX 0xE0XXXX Increments RDAC1 register by one to
0x102. Continue until desired wiper
position is reached.
0x20XXXX 0xXXXXXX Stores RDAC2 register data into
EEMEM1. Optionally, tie
WP
to GND to
protect EEMEM values.
The EEMEM values for the RDACs can be restored by power-
on, by strobing the
PR
pin, or by the two commands shown in
Table 16.
Table 16. Restoring the EEMEM Values to RDAC Registers
SDI SDO Action
0x10XXXX 0xXXXXXX Restores the EEMEM1 value to the
RDAC1 register.
Table 17. Using Left-Shift by One to Increment 6 dB Steps
SDI SDO Action
0xC0XXXX 0xXXXXXX Moves Wiper 1 to double the
present data contained in the
RDAC1 register.
0xC1XXXX 0xC0XXXX Moves Wiper 2 to double the
present data contained in the
RDAC2 register.
Table 18. Storing Additional User Data in EEMEM
SDI SDO Action
0x32AAAA 0xXXXXXX Stores Data 0xAAAA in the extra
EEMEM location USER1. (Allowable to
address in 13 locations with a
maximum of 16 bits of data.)
0x335555 0x32AAAA Stores Data 0x5555 in the extra
EEMEM location USER2. (Allowable to
address in 13 locations with a
maximum of 16 bits of data.)
Table 19. Reading Back Data from Memory Locations
SDI SDO Action
0x92XXXX
0xXXXXXX
Prepares data read from USER1
EEMEM location.
0x00XXXX 0x92AAAA NOP Instruction 0 sends a 24-bit word
out of SDO, where the last 16 bits
contain the contents in USER1 EEMEM
location.
Table 20. Reading Back Wiper Settings
SDI SDO Action
0xB00200
0xXXXXXX
Writes RDAC1 to midscale.
0xC0XXXX 0xB00200 Doubles RDAC1 from midscale to full
scale.
0xA0XXXX 0xC0XXXX Prepares reading wiper setting from
RDAC1 register.
0xXXXXXX
0xA003FF
Reads back full-scale value from SDO.
EVAL-AD5235SDZ EVALUATION KIT
Analog Devices, Inc., offers a user-friendly EVAL-AD5235SDZ
evaluation kit that can be controlled by a PC in conjunction
with the SDP platform. The driving program is self-contained;
no programming languages or skills are needed.