ds1847b-050t-r Maxim Integrated Products, Inc., ds1847b-050t-r Datasheet - Page 6

• Manufacturer Part Number: ds1847b-050t-r
• Description: Ds1847 Dual Temperature-controlled Nv Variable Resistor
• Manufacturer: Maxim Integrated Products, Inc.

PROGRAMMING THE LOOK-UP TABLE (LUT)
written in the LUT to achieve a given resistance at a specific temperature.
DS1847-050
a = 3.78964 for the 50kW resistor
a = 19.74866 for the 10kW resistor
DS1847-010
a = 8.394533 for both 10kW resistors
R = resistance desired at the output terminal
C = temperature in degrees Celsius
u, v, w, x, y, and z are calibration constants programmed into each of the corresponding look-up tables.
Their addresses and LSB values are given in Table 1. Resistor 1 variables are found in Look-Up Table 1
of the EEPROM, and Resistor 2 variables are found in Look-Up Table 2. After these values are read, they
should be overwritten with the appropriate temperature-specific resistance settings.
LOOK-UP VARIABLE ADDRESSES Table 1
When shipped from the factory, all other memory locations in the LUTs are programmed to FFh (except
bytes 00h-07h of Table 1 and 2 which may be factory programmed to values other than FFh).
Note: Memory locations 44h – 47h, which cover the temperature range (+96ºC to +102ºC), are outside
of the specified operating temperature range (-40ºC to +95ºC). However, the values stored in these
locations will act as valid resistance settings if the temperature exceeds +95ºC. Therefore, Dallas
Semiconductor recommends that the user programs a resistance value into all LUT locations. Failure to
do so will result in the part being set to the default value.
The following equation can be used to determine which resistor position setting, 00h – FFh, should be
LUT (HEX)
Address in
2A – 2B
2C – 2D
2E – 2F
28 – 29
30 – 31
32 – 33
Variable
w
u
v
x
y
z
pos
(
a
,
R
10
LSB
,
10
10
10
2
2
C
-8
-8
-10
)
-6
-9
-7
=
R
( )
-
x
u
·
·
[
1
[
1
+
+
y
v
·
·
6 of 17
(
C
(
C
-
-
25
25
)
)
+
+
z
w
·
·
(
C
(
C
-
-
25
25
)
2
)
]
2
]
-
a