MAXIM DS1848 User Manual

A
y
DS1848
Dual Temperature-Controlled
NV Variable Resistor & Memor
www.maxim-ic.com
FEATURES
§ Two linear taper, temperature-controlled variable resistors
§ DS1848-050
- One 50kW, 256 position
- One 10kW, 256 position
§ DS1848-010
- 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
§ 128 bytes of user EEPROM
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)
B
C
D
Top View
1 2 3 4
16-Ball CSBGA (4mm x 4mm)
DESCRIPTION
The DS1848 Dual Temperature-Controlled Nonvolatile (NV) Variable Resistor consists of two 256­position linear, variable resistors. The DS1848-050 consists of one 10kW and one 50kW, while the DS1848-010 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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DS1848
PIN DESCRIPTIONS
Name TSSOP BGA Description VCC 14 A3 Power Supply Terminal. The DS1848 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 DS1848. 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 DS1848 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 DS1848 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.
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DS1848
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DS1848 BLOCK DIAGRAM Figure 1
WP
A0
A1
A2
SD
SCL
Vcc
Gnd
2-Wire
Interface
0h
7Fh
Digital
Temperature
Sensor
128x8 bit
USER
EEPROM
(Table 0)
E0h
E1h
Table Select Byte
Configuration Byte
Temperature MSB
E2h
Temperature LSB
E3h
E4h
E5h-
Byte
Byte
Address Pointer
User Memory
E6h
Internal Address Sel
E7h
E8h-
User Memory
EFh
F0h
F1h
F2h-
FFh
Resistor 0 Setting
Resistor 1 setting
User Memory
72x8 bit
EEPROM
Resistor 0
Look-up Table
(Table 1)
72x8 bit
EEPROM
Resistor 1
Look-up Table
(Table 2)
256 Position
Digitally-
Controlled
10kW or 50kW
Resistor 0
256 Position
Digitally-
Controlled 10k
Resistor 1
0h
47h
H0
L0
H1
W
L1
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DS1848
Memory Location Name of Location Function of Location
00h to 47h
(the Table Select Byte, E0h, must be set to 01h or 02h to access the Look­Up Tables)
00h to 7Fh (the Table Select Byte, E0h, must be set to 00h to access the User EEPROM Memory)
User Defined Look-Up Table (LUT)
User Memory
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.
This block is for general-purpose user memory. When shipped from the factory, memory locations 60h – 6Bh contain the same information as found in Look-Up Table 1, memory locations 28h – 33h. Memory locations 6Ch – 77h contain the same information as found in Look-Up Table 2, memory locations 28h – 33h.
E0h Table Select Byte Writing to this byte determines if one of the two
72x8 EEPROM look-up tables or the user EEPROM memory is selected for reading or writing. 00h (User EEPROM selected) 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.
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DS1848
Memory Location Name of Location Function of Location
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.
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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DS1848
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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 -
DS1848-050
a = 3.78964 for the 50kW resistor a = 19.74866 for the 10kW resistor
DS1848-010 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 below. 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. Copies of these values can also be found in the User EEPROM memory.
LOOK-UP VARIABLE ADDRESSES Table1
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 program 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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