MAXIM DS1847 User Manual
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A
DS1847
Dual Temperature-Controlled
NV Variable Resisto
www.maxim-ic.com
FEATURES
§ Two linear taper, temperature-controlled
variable resistors
§ DS1847-050
- One 50kW, 256 position
- One 10kW, 256 position
§ DS1847-010
- Two 10kW, 256 position
§ Resistor settings changeable every 2°C
§ Access to temperature data and device
control via a 2-wire interface
§ Operates from 3V or 5V supplies
§ Packaging: 14-pin TSSOP, 16-ball CSBGA
§ Operating temperature: -40ºC to +95ºC
§ Programming temperature: 0ºC to +70ºC
PIN ASSIGNMENT
SDA 1 14 Vcc
SCL 2 13 H0
A0 3 12 NC
A1 4 11 H1
A2 5 10 L1
WP 6 9 NC
GND 7 8 L0
14-Pin TSSOP (173-mil)
Top View
B
C
D
1 2 3 4
16-Ball CSBGA (4mm x 4mm)
DESCRIPTION
The DS1847 Dual Temperature-Controlled Nonvolatile (NV) Variable Resistor consists of two 256-
position linear, variable resistors. The DS1847-050 consists of one 10kW and one 50kW, while the
DS1847-010 consists of two 10kW resistors; both incorporate a direct-to-digital temperature sensor. The
device provides an ideal method for setting and temperature-compensating bias voltages and currents in
control applications using a minimum of circuitry.
The variable resistors settings are stored in EEPROM memory and can be accessed over the industry
standard 2-wire serial bus. The value of each variable resistor is determined by a temperature-addressed
look-up table, which can assign a unique value to each resistor for every 2°C increment over the -40°C to
+95°C range. The output of the digital temperature sensor is also available as a 13-bit, 2’s complement
value over the serial bus. The interface I/O pins consist of SDA and SCL.
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PIN DESCRIPTIONS
Name TSSOP BGA Description
VCC 14 A3 Power Supply Terminal. The DS1847 will support supply
voltages ranging from +3.0V to +5.5V.
GND 7 D1 Ground Terminal.
SDA 1 B2 2-Wire Serial Data Interface. The serial data pin is for serial data
transfer to and from the DS1847. The pin is open drain and may
be wire-ORed with other open drain or open collector interfaces.
SCL 2 A2 2-Wire Serial Clock Input. The serial clock input is used to
clock data into the DS1847 on rising edges and clock data out on
falling edges.
WP 6 C1 Write Protect Input. If open or set to logic 1, all memory, control
registers, and Look-up tables
are write protected. If set to a logic 0, the device is not write protected and
can be written to. The WP pin is pulled high internally.
A0 3 A1 Address Input. Pins A0, A1, and A2 are used to specify the
address of each DS1847 when used in a multi-dropped
configuration.
A1 4 B1 Address Input.
A2 5 C2 Address Input.
H0 13 A4 High terminal of Resistor 0. For both resistors, it is
not required that the high terminal be connected to a potential
greater than the low terminal. Voltage applied to the high terminal
of each resistor cannot exceed VCC, or go below ground.
H1 11 B3 High terminal of Resistor 1.
L0 8 D3 Low terminal of Resistor 0. For both resistors, it is
not required that the low terminal be connected to a potential less
than the high terminal. Voltage applied to the low terminal of each
resistor cannot exceed VCC, or go below ground.
L1 10 C4 Low terminal of Resistor 1.
NC 9 D4 No Connect.
NC 12 B4 No Connect.
NC C3 No Connect.
NC D2 No Connect.
DS1847
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DS1847 BLOCK DIAGRAM Figure 1
A
WP
A0
A1
A2
SD
SCL
V
CC
Gnd
2-Wire
Interface
Digital
Temperature
Sensor
0h
47h
72x8 bit
EEPROM
Resistor 0
Look-up Table
(Table 1)
E0h
E1h
E2h
E3h
E4h
E5hE6h
E7h
E8hEFh
Resistor 0 Setting
F0h
F1h
F2hFFh
72x8 bit
EEPROM
Resistor 1
Look-up Table
(Table 2)
Table Select Byte
Configuration
Byte
Temperature
MSB Byte
Temperature
LSB Byte
Address Pointer
User Memory
Internal Address
Select
User Memory
Resistor 1 setting
User Memory
256 Position
Digitally-
Controlled
10kW or 50kW
Resistor 0
256 Position
Digitally-
Controlled 10kW
Resistor 1
DS1847
H0
L0
H1
L1
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DS1847
Memory
Name of Location Function of Location
Location
00h to 47h
(Table Select
Byte, E0h, must
be set to 01h or
02h to access the
Look-Up Tables)
User Defined Look-Up Table
(LUT)
This block contains the user defined temperature
settings of the resistors. Values between 00h and
FFh can be written to either table to set the 256
position variable resistors. The first address
location, 00h, is used to set the resistor at -40°C.
Each successive memory location will contain the
resistor setting for the previous temperature +2°C.
For example, memory address 01h is the address
that will set the resistor in a –38°C environment.
For default memory settings and programming
the look-up table, refer to the Programming the
Look-Up Table (LUT) section of the datasheet.
E0h Table Select Byte Writing to this byte determines which of the two
72x8 EEPROM look-up tables is selected for
reading or writing.
01h (Look-Up Table 1 selected)
02h (Look-Up Table 2 selected)
E1h Configuration Byte
TAU TEN AEN
TAU – Temperature/Address Update
TEN – Temperature Update Enable
AEN – Address Update Enable
Default setting is 03h, TAU = 1, TEN = 1 and
AEN = 1.
TAU becomes a 1 after a temperature and address
update has occurred as a result of a temperature
conversion. The user can write this bit to 0 and
check for a transition from 0 to 1 in order to
verify that a conversion has occurred.
If TEN = 0, the temperature conversion feature is
disabled. The user sets the resistor in “manual
mode” by writing to addresses F0h and
F1h to control resistors 0 and 1, respectively.
With AEN = 0 the user can operate in a test
mode. Address updates made from the
temperature sensor will cease. The user can load a
memory location into E4h and verify that the
values in locations F0h and F1h are the expected
user-defined values.
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DS1847
Memory
Name of Location Function of Location
Location
E2h Temperature MSB This byte contains the MSB of the 13-bit 2s
complement temperature output from the
temperature sensor.
S 27 26 25 24 23 22 21
E3h Temperature LSB This byte contains the LSB of the 13-bit 2s
complement temperature output from the
temperature sensor.
20 2-1 2-2 2-3 2-4 X X X
For example temperature readings, refer to Table
2.
E4h Address Pointer Calculated, current resistor address (0h – 47h).
The user-defined resistor setting at this location in
the respective look-up table will be loaded into
F0h and F1h to set the two resistors.
E5h to E6h User Memory General purpose user memory (SRAM)
E7h Address Select Internal or external device address select. This
byte allows the user to use the external address
pins or an internal register location to determine
the device address.
A2 A1 A0 ENB
ENB = 0 and external A2, A1, A0 grounded,
device will use internal address bits (A2, A1, A0)
in this register
ENB = 1, external A2, A1, A0 = any setting,
device will use external address pins
Default setting is 01h. The device uses external
pins to determine its address.
E8h to EFh User Memory General purpose user memory (SRAM)
F0h Resistor 0 Setting In the user-controlled setting mode, this block
contains the resistor 0 setting.
F1h Resistor 1 Setting In the user-controlled setting mode, this block
contains the resistor 1 setting.
F2h to FFh User memory General purpose user memory (SRAM)
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DS1847
[
]
PROGRAMMING THE LOOK-UP TABLE (LUT)
The following equation can be used to determine which resistor position setting, 00h – FFh, should be
written in the LUT to achieve a given resistance at a specific temperature.
),,(
CRpos
=
() ( ) ( )
[]
()()
CwCvuR
CzCyx
-·+-·+·
2
25251
-·+-·+·-
2
25251
aa -
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
Address in
LUT (HEX)
28 – 29 u 2-8
2A – 2B v 10-6
2C – 2D w 10-9
2E – 2F x 2-8
30 – 31 y 10-7
32 – 33 z 10
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.
Variable LSB
-10
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