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DS1841

Temperature-Controlled, NV, I

Logarithmic Resistor

Rev 0; 11/07

________________________________________________________________

Maxim Integrated Products

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

General Description

The DS1841 is a 7-bit, logarithmic, nonvolatile (NV) digi-

tal resistor that features an on-chip temperature sensor

and associated analog-to-digital converter (ADC). The

integrated temperature sensor indexes a 72-byte NV

lookup table (LUT) encompassing a temperature range

from -40°C to +100°C. The LUT output can drive the

resistor directly or be added to an NV initial-value regis-

ter (IVR) to drive the resistor. This flexible LUT-based

architecture allows the DS1841 to provide a tempera-

ture-compensated resistor output with arbitrary slope.

Programming is accomplished by an I

C-compatible

interface, which can operate at speeds of up to 400kHz.

Applications

Optical Transceivers

Linear and Nonlinear Compensation

Instrumentation and Industrial Controls

Mechanical Potentiometer Replacement

Features

♦ 22kΩ to 3.7kΩ Adjustable Logarithmic Resistor

with a 3.6kΩ Fixed Resistor

♦ 128 Wiper Tap Points

♦ On-Chip Temperature Sensor and ADC

♦ 72-Byte Lookup Table (LUT)

♦ I

C-Compatible Serial Interface

♦ Address Pins Allow Up to Four DS1841s to Share

the Same I

C Bus

♦ Digital Supply of 2.7V to 5.5V

♦ -40°C to +100°C Operating Range

♦ 3mm x 3mm, 10-Pin TDFN Package

134

10 8 7

SCL RH RW

SDA

*EP

*EXPOSED PAD

N.C.

GND

RGND

TDFN

3.0mm × 3.0mm × 0.8mm

TOP VIEW

DS1841

Pin Configuration

Ordering Information

0.1μF

3.3V

APD BIAS CONTROL APPLICATION

OUT

SDA

SCL

GND

100pF

RGND

APD

4.7kΩ

DC-DC

CONVERTER

DS1841

Typical Operating Circuit

Denotes a lead-free package.

T&R = Tape and reel.

Registers and Modes are capitalized for clarity.

PART TEMP RANGE PIN-PACKAGE

DS1841T+ -40°C to +100°C 10 TDFN

DS1841T+T&R -40°C to +100°C 10 TDFN

Summary of content (16 pages)

PAGE 1
Rev 0; 11/07 Temperature-Controlled, NV, I2C, Logarithmic Resistor The DS1841 is a 7-bit, logarithmic, nonvolatile (NV) digital resistor that features an on-chip temperature sensor and associated analog-to-digital converter (ADC). The integrated temperature sensor indexes a 72-byte NV lookup table (LUT) encompassing a temperature range from -40°C to +100°C. The LUT output can drive the resistor directly or be added to an NV initial-value register (IVR) to drive the resistor.
PAGE 2
DS1841 Temperature-Controlled, NV, I2C, Logarithmic Resistor ABSOLUTE MAXIMUM RATINGS Voltage Range on SDA, SCL, and VCC Relative to GND .........................................-0.5V to +6.0V Voltage Range on RH, RW, A0, and A1 Relative to GND ................................-0.5V to (VCC + 0.5V) Operating Temperature Range .........................-40°C to +100°C Programming Temperature Range .........................0°C to +70°C Storage Temperature Range .............................
PAGE 3
Temperature-Controlled, NV, I2C, Logarithmic Resistor (VCC = +2.7V to +5.5V, TA = -40°C to +100°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP Temperature Error Update Rate (Temperature and Supply Conversion Time) tFRAME MAX UNITS ±5 °C 16 ms ANALOG VOLTAGE MONITORING CHARACTERISTICS (VCC = +2.7V to +5.5V, TA = -40°C to +100°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP Supply Resolution LSB Full-scale voltage of 6.5536V 25.
PAGE 4
DS1841 Temperature-Controlled, NV, I2C, Logarithmic Resistor I2C AC ELECTRICAL CHARACTERISTICS (See Figure 3) (continued) (VCC = +2.7V to +5.5V, TA = -40°C to +100°C, timing referenced to VIL(MAX) and VIH(MIN).) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS 10 20 ms tW A0, A1 Setup Time t SU:A Before START 0.6 μs A0, A1 Hold Time tHD:A After STOP 0.
PAGE 5
Temperature-Controlled, NV, I2C, Logarithmic Resistor UPDATE MODE BIT = 0 100 50 LUT MODE AND LUT ADDER MODE UPDATE MODE BIT = 1 150 UPDATE MODE BIT = 0 100 3.5 4.0 4.5 5.0 UPDATE MODE BIT = 0 100 SDA SDA==SCL VCC==VCC 5V RGND, RH, RH, RH,RW RWARE AREFLOATING FLOATING 0 0 3.0 150 SDA SDA = SCL = SCL = V=CC VCC = 5V RGND, RH, RH, RH,RW RWARE AREFLOATING FLOATING 0 5.5 -40 -20 0 20 40 60 80 0 100 200 300 TEMPERATURE (°C) SCL FREQUENCY (kHz) WIPER RESISTANCE (RW) vs.
PAGE 6
Temperature-Controlled, NV, I2C, Logarithmic Resistor DS1841 Pin Description PIN NAME 1 SDA I2C Serial Data. Input/output for I2C data. 2 GND Ground 3 VCC Power Supply 4 A1 5 A0 Address Select Inputs. Determines I2C slave address. Device address is 01010A1 A0X (see the Slave Address Byte and Address Pins sections for more details). 6 RGND 7 RW Wiper Terminal 8 RH Terminal with Fixed Resistor Added in Series with Digital Resistor No Connection 9 N.C.
PAGE 7
Temperature-Controlled, NV, I2C, Logarithmic Resistor in the IVR is added to the values stored in the LUT. The dashed line/arrow shown in the LUT Drive Mode Block Diagram is not active in LUT Mode. When in LUT Mode, on power-up the IVR value is recalled into the WR. This value remains there until completion of the first temperature conversion following power-up. The temperature is measured every tFRAME. The temperature value is used to calculate an index that points to the corresponding value in the LUT.
PAGE 8
Temperature-Controlled, NV, I2C, Logarithmic Resistor DS1841 LUT Mode and LUT Adder Mode Block Diagram (Update Mode Bit = 1) VCC A0 CONTROL I 2C INTERFACE DATA A1 TEMP SENSOR TEMP 0Ch ADC VCC VOLTAGE VCC (V) 0Eh LUT ADDRESS REGISTER 72-BYTE LOOKUP TABLE (LUTAR) (LUT) 08h 80h–C7h WIPER REGISTER LUTVAL ∑ LUTVAL OR LUTVAL+IVR (WR) 09h* RGND POS 7Fh 1 OF 128 MULTIPLEXERS SCL SDA INITIAL VALUE REGISTER (IVR) 00h* ON POWER-UP CONTROL LOGIC/ REGISTERS IVR ONLY WHEN IN LUT ADDER MODE GND P
PAGE 9
Temperature-Controlled, NV, I2C, Logarithmic Resistor DECREASING TEMPERATURE MEMORY LOCATION LUT34 LUT33 LUT32 INCREASING TEMPERATURE LUT31 LUT30 1°C HYSTERESIS WINDOW 19 21 23 25 19 27 TEMPERATURE (°C) Figure 1. LUT Hysteresis Supply Current (ICC) The DS1841 has two supply current levels of power supply consumption. First, active current during I2C communications while in the LUT-Driven Mode is the “worst case” supply current, ICC.
PAGE 10
DS1841 Temperature-Controlled, NV, I2C, Logarithmic Resistor Memory Description The DS1841’s internal memory consists of both volatile and NV registers that are organized into eight byte rows. Three control registers as well as specialized data registers are used to control the wiper and drive the LUT.
PAGE 11
Temperature-Controlled, NV, I2C, Logarithmic Resistor FACTORY DEFAULT MEMORY TYPE 03h Reserved Bit 7 Bits 7 to 2 Bit 1 Bit 0 Reserved 00h Shadowed NV Reserved Reserved Reserved Reserved Adder Mode Update Mode Bit 0 Reserved. Adder Mode This bit is valid only if the Update Mode bit = 1. 0 = (Default) The LUTVAL or IVR value is directly loaded to WR though the mux. 1 = The LUTVAL is summed with the IVR value and is directly loaded to WR though the mux. Update Mode 0 = (Default) CR0 is enabled.
PAGE 12
DS1841 Temperature-Controlled, NV, I2C, Logarithmic Resistor Register 0Ah: Control Register 2 (CR2) FACTORY DEFAULT MEMORY TYPE 0Ah Reserved 00h Volatile Reserved Reserved Reserved Reserved Wiper Access Control LUTAR Mode Reserved Bit 7 Bits 7 to 3 Bit 2 Bit 1 Bit 0 Bit 0 Reserved. Wiper Access Control This bit is valid only in LUT Mode and in LUT Adder Mode.
PAGE 13
Temperature-Controlled, NV, I2C, Logarithmic Resistor FACTORY DEFAULT MEMORY TYPE 80h to C7h DS1841 Registers 80h to C7h: Temperature Lookup Register (LUT) 00h NV (See Table 3 for settings.) Bit 7 Bit 0 These registers at location 80h to C7h are NV and serve to temperature compensate RW over the operating temperature range of the DS1841. The LUT entries are unsigned 8-bit values if the Adder Mode bit = 0. If the Adder Mode bit = 1, LUT entries are two’s complement, signed 7-bit values.
PAGE 14
DS1841 Temperature-Controlled, NV, I2C, Logarithmic Resistor SDA tBUF tHD:STA tLOW tR tSP tF SCL tHD:STA STOP tSU:STA tHIGH tSU:DAT START REPEATED START tSU:STO tHD:DAT NOTE: TIMING IS REFERENCE TO VIL(MAX) AND VIH(MIN). Figure 3. I2C Timing Diagram Byte read: A byte read is an 8-bit information transfer from the slave to the master plus a 1-bit ACK or NACK from the master to the slave.
PAGE 15
Temperature-Controlled, NV, I2C, Logarithmic Resistor counter. To read a single byte from the slave, the master generates a START condition, writes the slave address byte with R/W = 1, reads the data byte with a NACK to indicate the end of the transfer, and generates a STOP condition. However, since requiring the master to keep track of the memory address counter is impractical, the following method should be used to perform reads from a specified memory location.
PAGE 16
DS1841 Temperature-Controlled, NV, I2C, Logarithmic Resistor tion, writes the slave address byte (R/W = 1), reads data with ACK or NACK as applicable, and generates a STOP condition. See Figure 4 for I2C Communication Examples. tance, which improves performance, and ceramic capacitors tend to have adequate high-frequency response for decoupling applications. Applications Information SDA is an I/O with an open-collector output that requires a pullup resistor to realize high-logic levels.