ADN2850BCP250-RL7 Analog Devices Inc, ADN2850BCP250-RL7 Datasheet - Page 19

• Manufacturer Part Number: ADN2850BCP250-RL7
• Description: IC DGTL RHEO DL 25K 9BIT16LFCSP
• Manufacturer: Analog Devices Inc

Specifications of ADN2850BCP250-RL7

• Rohs Status: RoHS non-compliant
• Taps: 1024
• Resistance (ohms): 250K
• Number Of Circuits: 2
• Temperature Coefficient: 35 ppm/°C Typical
• Memory Type: Non-Volatile
• Interface: 4-Wire SPI Serial
• Voltage - Supply: 3 V ~ 5.5 V, ±2.25 V ~ 2.75 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-LFCSP
• Resistance In Ohms: 250K
• For Use With: EVAL-ADN2850-25EBZ - BOARD EVALUATION FOR ADN2850-25

PROGRAMMING THE VARIABLE RESISTOR
The nominal resistance of the RDAC between Terminal W and
Terminal B, R
1024 positions (10-bit resolution). The final digits of the part
number determine the nominal resistance value, for example,
25 kΩ = 24.4 Ω; 250 kΩ = 244 Ω.
The 10-bit data-word in the RDAC latch is decoded to select one of
the 1024 possible settings. The following description provides the
calculation of resistance, R
The first connection of the wiper starts at Terminal B for
Data 0x000. R
it is independent of the nominal resistance. The second connection
is the first tap point where R
for Data 0x001. The third connection is the next tap point
representing R
and so on. Each LSB data value increase moves the wiper up the
resistor ladder until the last tap point is reached at R
25006 Ω. See Figure 32 for a simplified diagram of the equivalent
RDAC circuit.
The general equation that determines the programmed output
resistance between Terminal Bx and Terminal Wx is
where:
D is the decimal equivalent of the data contained in the RDAC
register.
R
R
Table 13. R
D (Dec)
1023
512
1
0
Note that, in the zero-scale condition, a finite wiper resistance
WB_NOM
W
100
is the wiper resistance.
75
50
25
0
R
0
WB
is the nominal resistance value
(
D
)
WB
R
25,006
12,530
54.4
30
=
WB
WB
WB
WB
1024
(D) at Selected Codes for R
(D) (Ω)
(0) is 30 Ω because of the wiper resistance, and
, is available with 25 kΩ and 250 kΩ with
D
(2) = 48.8 Ω + 30 Ω = 78.8 Ω for Data 0x002,
Figure 33. R
256
×
R
WB
WB
_
Output State
Full scale
Midscale
1 LSB
Zero scale (wiper contact resistor)
CODE (Decimal)
WB
NOM
, at different codes of a 25 kΩ part.
WB
(1) becomes 24.4 Ω + 30 Ω = 54.4 Ω
(D) vs. Decimal Code
512
+
R
W
WB_NOM
768
R
WB
= 25 kΩ
WB
(1023) =
1023
Rev. C | Page 19 of 28
(1)
of 30 Ω is present. Care should be taken to limit the current
flow between W and B in this state to no more than 20 mA to
avoid degradation or possible destruction of the internal switches.
The typical distribution of R
±0.2% within the same package. Device-to-device matching is
process lot dependent upon the worst case of ±30% variation.
However, the change in R
35 ppm/°C temperature coefficient.
PROGRAMMING EXAMPLES
The following programming examples illustrate a typical sequence
of events for various features of the ADN2850. See Table 8 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
0xB00100
0xB10200
Table 15. Incrementing RDAC Followed by Storing the
Wiper Setting to EEMEM
SDI
0xB00100
0xE0XXXX
0xE0XXXX
0x20XXXX
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
0x10XXXX
.
SDO
0xXXXXXX
0xB00100
SDO
0xXXXXXX
SDO
0xXXXXXX
0xB00100
0xE0XXXX
0xXXXXXX
WB
Action
Writes Data 0x100 into RDAC1 register,
Wiper W1 moves to 1/4 full-scale
position.
Loads Data 0x200 into RDAC2 register,
Wiper W2 moves to 1/2 full-scale
position.
Action
Restores the EEMEM1 value to the
RDAC1 register.
Action
Writes Data 0x100 into RDAC1
register, Wiper W1 moves to 1/4 full-
scale position.
Increments RDAC1 register by one to
0x101.
Increments RDAC1 register by one to
0x102. Continue until desired wiper
position is reached.
Stores RDAC2 register data into
EEMEM1. Optionally, tie WP to GND to
protect EEMEM values.
at full scale with temperature has a
WB_NOM
from channel to channel is
ADN2850