DS1847
Dual Temperature-Controlled
NV Variable Resistor
www.maxim-ic.com
FEATURES
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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
SCL
A0
A1
A2
WP
GND
1
2
3
4
5
6
7
14
13
12
11
10
9
8
Vcc
H0
NC
H1
L1
NC
L0
14-Pin TSSOP (173-mil)
Top View
A
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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011806
DS1847
PIN DESCRIPTIONS
Name TSSOP BGA
V
CC
14
A3
GND
SDA
SCL
WP
7
1
2
6
D1
B2
A2
C1
Description
Power Supply Terminal.
The DS1847 will support supply
voltages ranging from +3.0V to +5.5V.
Ground Terminal.
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.
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.
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.
Address Input.
Pins A0, A1, and A2 are used to specify the
address of each DS1847 when used in a multi-dropped
configuration.
Address Input.
Address Input.
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 V
CC
, or go below ground.
High terminal of Resistor 1.
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 V
CC
, or go below ground.
Low terminal of Resistor 1.
No Connect.
No Connect.
No Connect.
No Connect.
A0
A1
A2
H0
3
4
5
13
A1
B1
C2
A4
H1
L0
11
8
B3
D3
L1
NC
NC
NC
NC
10
9
12
C4
D4
B4
C3
D2
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DS1847
DS1847 BLOCK DIAGRAM
Figure 1
WP
A0
A1
A2
SDA
SCL
V
CC
Gnd
2-Wire
Interface
0h
72x8 bit
EEPROM
Resistor 0
Look-up Table
(Table 1)
E0h
E1h
E2h
72x8 bit
EEPROM
Resistor 1
Look-up Table
(Table 2)
47h
Table Select Byte
Configuration
Byte
Temperature
MSB Byte
Temperature
LSB Byte
Address Pointer
User Memory
Internal Address
Select
User Memory
Resistor 0 Setting
Resistor 1 setting
User Memory
256 Position
Digitally-
Controlled
10kW or 50kW
Resistor 0
256 Position
Digitally-
Controlled 10kW
Resistor 1
Digital
Temperature
Sensor
E3h
E4h
E5h-
E6h
E7h
E8h-
EFh
F0h
F1h
F2h-
FFh
H0
L0
H1
L1
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DS1847
Memory
Location
00h to 47h
(Table Select
Byte, E0h, must
be set to 01h or
02h to access the
Look-Up Tables)
Name of Location
User Defined Look-Up Table
(LUT)
Function of Location
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.
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)
TAU TEN AEN
E0h
Table Select Byte
E1h
Configuration Byte
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
Location
E2h
Name of Location
Temperature MSB
Function of Location
This byte contains the MSB of the 13-bit 2s
complement temperature output from the
temperature sensor.
S 2
7
2
6
2
5
2
4
2
3
2
2
2
1
This byte contains the LSB of the 13-bit 2s
complement temperature output from the
temperature sensor.
2
0
2
-1
2
-2
2
-3
2
-4
X X X
For example temperature readings, refer to Table
2.
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.
General purpose user memory (SRAM)
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
E3h
Temperature LSB
E4h
Address Pointer
E5h to E6h
E7h
User Memory
Address Select
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.
General purpose user memory (SRAM)
In the user-controlled setting mode, this block
contains the resistor 0 setting.
In the user-controlled setting mode, this block
contains the resistor 1 setting.
General purpose user memory (SRAM)
E8h to EFh
F0h
F1h
F2h to FFh
User Memory
Resistor 0 Setting
Resistor 1 Setting
User memory
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