Datasheet

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General Description

The DS3906 is intended for low resistance, small step-

size applications. It contains three nonvolatile (NV), low-

temperature coefficient, variable digital resistors that

are capable of ohm and subohm increments when

used in parallel with a fixed external resistor. All three of

the DS3906’s resistors have 64 positions (plus a high-Z

state) with a pseudo-log response cleverly chosen to

have a linear equivalent resistance when paired with an

external resistor (see graphs below). The DS3906 also

contains 16 bytes of user EEPROM that, in addition to

the resistors, are controlled through an I

C-compatible

serial interface. Three address pins allow up to eight

DS3906s to be placed on the same I

C bus.

The DS3906 can also be factory cutomized to provide a

variety of transfer functions depending on user

requirements. Contact mixedsignal.apps@dalsemi.com

for additional information.

Applications

Low Ohm, Fine Resolution Driver Control for LED

Display Panels

Low Ohm, Fine Resolution Instrumentation Control

Features

♦ Three Programmable Resistors for Low Step-Size

Applications (Ohm and Subohm)

♦ Resistor Settings are NV

♦ 16-Byte NV User Memory (EEPROM)

♦ I

C-Compatible Serial Interface

♦ Up to 8 Devices Can be Multidropped on the

Same I

C Bus

♦ Low Power Consumption

♦ Wide Operating Voltage (2.7V to 5.5V)

♦ Operating Temperature Range: -40°C to +85°C

DS3906

Triple NV Low Step Size Variable

Resistor Plus Memory

______________________________________________ Maxim Integrated Products 1

TOP VEIW

101

SDA

μSOP

83H0SCL

H1V

H2GND

DS3906

Pin Configuration

DS3906

R0 R

EXT0

R1 R

EXT1

R2 R

EXT2

RESISTOR 0 AND 1 RESISTANCE vs. POSITION

(WITH AND WITHOUT EXTERNAL RESISTOR)

RESISTOR POSITION (dec)

EFFECTIVE

= R

0, 1

|| R

EXT

(Ω)

0, 1

WITHOUT R

EXT

(Ω)

483216

100

120

140

160

180

200

500

100

1500

2000

2500

3000

064

0, 1

|| (R

EXT

= 150Ω)

0, 1

|| (R

EXT

= 105Ω)

0, 1

|| (R

EXT

= 50Ω)

0, 1

WITHOUT R

EXT

RESISTOR 2 RESISTANCE vs. POSITION

(WITH AND WITHOUT EXTERNAL RESISTOR)

RESISTOR POSITION (dec)

EFFECTIVE

= R

|| R

EXT

(Ω)

483216

100

150

200

250

300

350

064

WITHOUT R

EXT

(Ω)

600

800

1000

1200

1400

1600

400

|| (R

EXT

= 400Ω)

|| (R

EXT

= 310Ω)

|| (R

EXT

= 250Ω)

WITHOUT R

EXT

Resistor Plots

Rev 1; 2/06

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

+Denotes lead-free package.

T&R denotes tape-and-reel package.

Ordering Information

Typical Operating Circuit appears at end of data sheet.

PART TEMP RANGE PIN-PACKAGE

DS3906U -40°C to +85°C 10 µSOP

DS3906U+ -40°C to +85°C 10 µSOP

DS3906U+T&R -40°C to +85°C 10 µSOP

DS3906U/T&R -40°C to +85°C 10 µSOP

Summary of content (14 pages)

PAGE 1
Rev 1; 2/06 Triple NV Low Step Size Variable Resistor Plus Memory Features The DS3906 is intended for low resistance, small stepsize applications. It contains three nonvolatile (NV), lowtemperature coefficient, variable digital resistors that are capable of ohm and subohm increments when used in parallel with a fixed external resistor.
PAGE 2
DS3906 Triple NV Low Step Size Variable Resistor Plus Memory ABSOLUTE MAXIMUM RATINGS Voltage on VCC, SDA, SCL, and H0-H2 Pins Relative to Ground.............................................-0.5V to +6.0V Voltage on A0, A1, and A2 Relative to Ground .....-0.5V to VCC + 0.5V, not to exceed +6.0V Resistor Current ....................................................................5mA Operating Temperature Range ...........................-40°C to +85°C EEPROM Programming Temperature Range .........
PAGE 3
Triple NV Low Step Size Variable Resistor Plus Memory DS3906 AC ELECTRICAL CHARACTERISTICS (See Figure 2) (VCC = +2.7V to 5.5V, TA = -40°C to +85°C, unless otherwise noted. Timing referenced to VIL(MAX) and VIH(MIN).) PARAMETER SYMBOL CONDITIONS TYP UNITS 400 kHz fSCL Bus Free Time Between Stop and Start Conditions tBUF 1.3 µs tHD:STA 0.6 µs tLOW 1.3 µs Low Period of SCL High Period of SCL 0 MAX SCL Clock Frequency Hold Time (Repeated) Start Condition (Note 5) MIN tHIGH 0.
PAGE 4
Typical Operating Characteristics (VCC = +5.0V, TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. SUPPLY VOLTAGE SUPPLY CURRENT vs. TEMPERATURE 120 100 80 60 VCC = 3.3V 120 100 80 60 40 40 20 20 SDA/SCL = VCC ADDRESS PINS CONNECTED TO GND 3.70 3.20 4.20 4.70 5.20 80 60 VCC = SDA = 5V ADDRESS PINS CONNECTED TO GND 20 0 -40 -15 10 35 85 60 0 100 150 200 250 300 350 400 50 SCL FREQUENCY (kHz) RESISTORS (R0,1) vs. RESISTOR SETTING RESISTOR R2 vs.
PAGE 5
Triple NV Low Step Size Variable Resistor Plus Memory 250 200 150 100 50 0 50 30 20 40 RESISTOR SETTING (dec) 60 5 0 -5 -10 -15 -20 -25 70 0 10 50 30 20 40 RESISTOR SETTING (dec) 60 +25°C TO +85°C DS3906 toc11 160 140 120 100 80 60 40 20 0 70 0 50 30 20 40 RESISTOR SETTING (dec) 10 60 70 R0,1 RESISTANCE AT POSITION 2Fh vs. POWER-UP VOLTAGE 2000 1500 RESISTOR R2 AT POSITION 1Fh 1000 500 5000 R0,1 RESISTANCE AT POSITION 2Fh (Ω) DS3906 toc12 RESISTANCE vs.
PAGE 6
Typical Operating Characteristics (continued) (VCC = +5.0V, TA = +25°C, unless otherwise noted.) INL vs. RESISTOR SETTING FOR (R0 REXT) (R0 REXT) REXT = 87Ω 1.5 3000 1.0 DS3906 toc17 3500 >5.5MΩ RESISTOR R2 2.0 DS3906 toc16 4000 DNL vs. RESISTOR SETTING FOR (R0 REXT) DS3906 toc18 R2 RESISTANCE AT POSITION 1Fh vs. POWER-UP VOLTAGE (R0 REXT) REXT = 87Ω 0.8 0.6 1.0 0.4 EEPROM RECALL 2000 1500 0.5 DNL (LSB) 2500 INL (LSB) 0 -0.5 PROGRAMMED VALUE 1000 0.2 0 -0.2 -0.4 -1.0 -0.
PAGE 7
Triple NV Low Step Size Variable Resistor Plus Memory PIN NAME 1 A1 FUNCTION 2 SDA I2C Serial Data Open-Drain Input/Output 3 SCL I2C Serial Clock Input 4 VCC Power Supply Voltage 5 GND 6 H2 High Terminal of Resistor 2 7 H1 High Terminal of Resistor 1 8 H0 High Terminal of Resistor 0 9 A0 10 A2 I2C Address Input. Inputs A0, A1, and A2 determine the I2C slave address of the device. Ground I2C Address Input. Inputs A0, A1, and A2 determine the I2C slave address of the device.
PAGE 8
DS3906 Triple NV Low Step Size Variable Resistor Plus Memory makes the corresponding resistor go High-Z. Plots for both resistor sizes are shown on the front page of this data sheet. It can be seen that, when an external resistor is connected in parallel with the DS3906’s resistors, the effective resistance is linear and capable of achieving sub-ohm and ohm steps. The resistor settings are stored in EEPROM memory. It is important to point out that the DS3906 EEPROM is organized in 2-byte pages.
PAGE 9
Triple NV Low Step Size Variable Resistor Plus Memory DS3906 Table 3. DS3906 Resistor Settings (without external resistor) POSITION NOMINAL RESISTOR VALUES WITHOUT EXT RESISTOR (25°C) POSITION NOMINAL RESISTOR VALUES WITHOUT EXT RESISTOR (25°C) Dec Hex Resistors 0, 1 Resistor 2 Dec Hex Resistors 0, 1 Resistor 2 0 00 175.0 469.7 32 20 396.1 768.4 1 01 178.8 476.4 33 21 409.1 781.7 2 02 182.7 483.2 34 22 422.9 795.4 3 03 186.8 490.1 35 23 437.5 809.4 4 04 190.
PAGE 10
DS3906 Triple NV Low Step Size Variable Resistor Plus Memory External Resistor Selection/Considerations Using an external resistor in parallel with any of the DS3906’s resistors makes the effective resistance linear with small increments from position to position. Typical values for the external resistors are 87Ω for Resistor 0 and 1 and 258Ω for Resistor 2. The effective resistance will be the most linear when these values are used.
PAGE 11
Triple NV Low Step Size Variable Resistor Plus Memory Bit Read: At the end a write operation, the master must release the SDA bus line for the proper amount of setup time (see Figure 2) before the next rising edge of SCL during a bit read. The device shifts out each bit of data on SDA at the falling edge of the previous SCL pulse and the data bit is valid at the rising edge of the current SCL pulse. Remember that the master generates all SCL clock pulses including when it is reading bits from the slave.
PAGE 12
DS3906 Triple NV Low Step Size Variable Resistor Plus Memory Acknowledge Polling: Any time an EEPROM page is written, the DS3906 requires the EEPROM write time (tW) after the stop condition to write the contents of the page to EEPROM. During the EEPROM write time, the device does not acknowledge its slave address because it is busy. It is possible to take advantage of this phenomenon by repeatedly addressing the DS3906, which allows communication to continue as soon as the DS3906 is ready.
PAGE 13
Triple NV Low Step Size Variable Resistor Plus Memory Application Information Power Supply Decoupling To achieve best results, it is highly recommended that a decoupling capacitor is used on the I.C. power supply pins. Typical values of decoupling capacitors are 0.01µF and 0.1µF. Use a high-quality, ceramic, surface-mount capacitor, and mount it as close as possible to the VCC and GND pins of the I.C. to minimize lead inductance.
PAGE 14
DS3906 Triple NV Low Step Size Variable Resistor Plus Memory Package Information Chip Topology TRANSISTOR COUNT: 16,200 SUBSTRATE CONNECTED TO GROUND For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo. Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.