DS1847E-050+ ,Dual Temperature-Controlled NV Variable ResistorPIN DESCRIPTIONS Name TSSOP BGA Description V 14 A3 Power Supply Terminal. The DS1847 ..
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DS1847E-050+
Dual Temperature-Controlled NV Variable Resistor
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)
FEATURES Two linear taper, temperature-controlled
variable resistors
DS1847-050 One 50k, 256 position One 10k, 256 position
DS1847-010 Two 10k, 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
DESCRIPTION The DS1847 Dual Temperature-Controlled Nonvolatile (NV) Variable Resistor consists of two256-
position linear, variable resistors. The DS1847-050 consists of one 10kand one 50k, while the
DS1847-010 consists of two 10k 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.
DS1847
Dual Temperature-Controlled
NV Variable Resistor
1 2 3 4
Top View
16-Ball CSBGA (4mm x 4mm)
DS1847
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
DS1847 BLOCK DIAGRAM Figure 1
2-Wire
Interface
Digital
Temperature
Sensor
256 Position
Digitally-
Controlled
10k or 50k
Resistor 0
256 Position
Digitally-
Controlled 10k
Resistor 1
SDA
SCL
L0
72x8 bit
EEPROM
Resistor 0
Look-up Table
(Table 1)
72x8 bit
EEPROM
Resistor 1
Look-up Table
(Table 2)
VCC
Gnd
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
E0h
E1h
E2h
E3h
E4h
E5h-
E6h
E7h
E8h-
EFh
F0h
F1h
F2h-
FFh
0h
47h
DS1847
Memory
Location
Name of Location Function of 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 – 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.
TAU TEN AEN
DS1847
Memory
Location
Name of Location Function of Location
E2h Temperature MSB This byte contains the MSB of the 13-bit 2s
complement temperature output from the
temperature sensor.
E3h Temperature LSB This byte contains the LSB of the 13-bit 2s
complement temperature output from the
temperature sensor.
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.
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)
A2 A1 A0 ENB0 2-1 2-2 2-3 2-4 X X X
S 27 26 25 24 23 22 21
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. 2251251),,(zCyxwCvuRCRpos
DS1847-050
= 3.78964 for the 50k resistor
= 19.74866 for the 10k resistor
DS1847-010
= 8.394533 for both 10k 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)
Variable LSB
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 10-10
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.
DS1847
TEMPERATURE CONVERSION
The direct-to-digital temperature sensor measures temperature through the use of an on-chip temperature
measurement technique with an operating range from -40°C to +95°C. Temperature conversions are
initiated upon power-up, and the most recent result is stored in address locations E2h and E3h, which are
updated every 10ms. Temperature conversion will not occur during an active read or write to memory.
The value of each resistor is determined by the temperature-addressed look-up table that assigns a unique
value to each resistor for every 2°C increment with a 1°C hysteresis at a temperature transition over the
operating temperature range. This can be seen in Figure 2.
TEMPERATURE CONVERSION HYSTERESIS Figure 2
EXAMPLE TEMPERATURE READINGS Table 2
TEMP BINARY DATA HEX DATA
+95ºC 0010 1111 1000 0000 2F80h
+25.0625ºC 0000 1100 1000 1000 0C88h
-10.125ºC 1111 1010 1111 0000 FAF0h
-40ºC 1110 1100 0000 0000 EC00h
2 4 6 8 10 12
TEMPERATURE (C)
M6
MEMO
CAT
Increasing temp
Decreasing temp
DS1847
2-WIRE OPERATION
Clock and Data Transitions: The SDA pin is normally pulled high with an external resistor or device.
Data on the SDA pin may only change during SCL low time periods. Data changes during SCL high
periods will indicate a start or stop conditions depending on the conditions discussed below. Refer to the
timing diagram (Figure 4) for further details.
Start Condition: A high-to-low transition of SDA with SCL high is a start condition that must precede
any other command. Refer to the timing diagram (Figure 4) for further details.
Stop Condition: A low-to-high transition of SDA with SCL high is a stop condition. After a read
sequence, the stop command places the DS1847 into a low-power mode. Refer to the timing diagram
(Figure 4) for further details.
Acknowledge Bit: All address and data byte are transmitted via a serial protocol. The DS1847 pulls the
SDA line low during the ninth clock pulse to acknowledge that it has received each word.
Standby Mode: The DS1847 features a low-power mode that is automatically enabled after power-on,
after a stop command, and after the completion of all internal operations.
2-Wire Interface Reset: After any interruption in protocol, power loss, or system reset, the following
steps reset the DS1847:
1. Clock up to nine cycles.
2. Look for SDA high in each cycle while SCL is high.
3. Create a START condition while SDA is high.
Device Addressing: The DS1847 must receive an 8-bit device address word following a START
condition to enable a specific device for a read or write operation. The address word is clocked into the
DS1847 MSB to LSB. The address word consists of Ah (1010) followed by A2, A1, and A0 then the
R/W (READ/WRITE) bit. If the R/W bit is high, a read operation is initiated. If the R/W is low, a write
operation is initiated. For a device to become active, the values of A2, A1 and A0 must be the same as the
hard-wired address pins on the DS1847. Upon a match of written and hard-wired addresses, the DS1847
will output a zero for one clock cycle as an acknowledge. If the address does not match, the DS1847
returns to a low-power mode.
Write Operations: After receiving a matching address byte with the R/W bit set low, the device goes
into the write mode of operation. The master must transmit an 8-bit EEPROM memory address to the
device to define the address where the data is to be written. After this byte has been received, the DS1847
will transmit a zero for one clock cycle to acknowledge the receipt of the address. The master must then
transmit an 8-bit data word to be written into this address. The DS1847 will again transmit a zero for one
clock cycle to acknowledge the receipt of the data. At this point, the master must terminate the write
operation with a STOP condition. The DS1847 then enters an internally timed write process tw to the
EEPROM memory. All inputs are disabled during this byte write cycle.
The DS1847 is capable of an 8-byte page write. A page write is initiated the same way as a byte write, but
the master does not send a STOP condition after the first byte. Instead, after the slave acknowledges
receipt of the data byte, the master can send up to seven more bytes using the same nine-clock sequence.
DS1847
The master must terminate the write cycle with a STOP condition or the data clocked into the DS1847
will not be latched into permanent memory.
Acknowledge Polling: Once the internally-timed write has started and the DS1847 inputs are disabled,
acknowledge polling can be initiated. The process involves transmitting a START condition followed by
the device address. The R/W bit signifies the type of operation that is desired. The read or write sequence
will only be allowed to proceed if the internal write cycle has completed and the DS1847 responds with a
zero.
Read Operations: After receiving a matching address byte with the R/W bit set high, the device goes
into the read mode of operation. There are three read operations: current address read, random read, and
sequential address read.
CURRENT ADDRESS READ
The DS1847 has an internal address register that maintains the address used during the last read or write
operation, incremented by one. This data is maintained as long as VCC is valid. If the most recent address
was the last byte in memory, then the register resets to the first address. This address stays valid between
operations as long as power is available.
Once the device address is clocked in and acknowledged by the DS1847 with the R/W bit set to high, the
current address data word is clocked out. The master does not respond with a zero, but does generate a
STOP condition afterwards.
RANDOM READ
A random read requires a dummy byte write sequence to load in the data word address. Once the device
and data address bytes are clocked in by the master and acknowledged by the DS1847, the master must
generate another START condition. The master now initiates a current address read by sending the device
address with the read/write bit set high. The DS1847 will acknowledge the device address and serially
clocks out the data byte.
SEQUENTIAL ADDRESS READ
Sequential reads are initiated by either a current address read or a random address read. After the master
receives the first data byte, the master responds with an acknowledge. As long as the DS1847 receives
this acknowledge after a byte is read, the master may clock out additional data words from the DS1847.
After reaching address FFh, it resets to address 00h.
The sequential read operation is terminated when the master initiates a stop condition. The master does
not respond with a zero.
For a more detailed description of 2-wire theory of operation, refer to the next section.
