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MAX5477中文资料

General Description

The MAX5477/MAX5478/MAX5479 nonvolatile, dual, linear-taper, digital potentiometers perform the function of a mechanical potentiometer, but replace the mechanics with a simple 2-wire digital interface. Each device performs the same function as a discrete poten-tiometer or variable resistor and has 256 tap points.

The devices feature an internal, nonvolatile EEPROM used to store the wiper position for initialization during power-up. A write-protect feature prevents accidental overwrites of the EEPROM. The fast-mode I 2C-compati-ble serial interface allows communication at data rates up to 400kbps, minimizing board space and reducing interconnection complexity in many applications. Three address inputs allow a total of eight unique address combinations.

The MAX5477/MAX5478/MAX5479 provide three nomi-nal resistance values: 10k ?(MAX5477), 50k ?(MAX5478), or 100k ?(MAX5479). The nominal resistor temperature coefficient is 35ppm/°C end-to-end and 5ppm/°C ratiometric. The low temperature coefficient makes the devices ideal for applications requiring a low-temperature-coefficient variable resistor, such as low-drift, programmable gain-amplifier circuit configurations.The MAX5477/MAX5478/MAX5479 are available in 16-pin 3mm x 3mm x 0.8mm thin QFN and 14-pin 4.4mm x 5mm TSSOP packages. These devices operate over the extended -40°C to +85°C temperature range.

Applications

Mechanical Potentiometer Replacement Low-Drift Programmable-Gain Amplifiers Volume Control

Liquid-Crystal Display (LCD) Contrast Control

Features

?Power-On Recall of Wiper Position from Nonvolatile Memory ?EEPROM Write Protection

?Tiny 3mm x 3mm x 0.8mm Thin QFN Package ?35ppm/°C End-to-End Resistance Temperature Coefficient ?5ppm/°C Ratiometric Temperature Coefficient ?Fast 400kbps I 2C ?-Compatible Serial Interface ?1μA (max) Static Supply Current

Single-Supply Operation: +2.7V to +5.25V

?256 Tap Positions per Potentiometer ?±0.5 LSB DNL in Voltage-Divider Mode ?±1 LSB INL in Voltage-Divider Mode

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

________________________________________________________________Maxim Integrated Products

Functional Diagram

19-3379; Rev 2; 12/04

For pricing, delivery, and ordering information,please contact Maxim/Dallas Direct!at 1-888-629-4642, or visit Maxim’s website at https://www.wendangku.net/doc/e310837606.html,.

Pin Configurations appear at end of data sheet.

?Purchase of I 2C components from Maxim Integrated Products, Inc. or one of its sublicensed Associated

Companies, conveys a license under the Philips I 2C Patent Rights to use these components in an I 2C system, provided that the system conforms to the I 2C Standard Specification as defined by Philips.

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V DD = +2.7V to +5.25V, H_ = V DD , L_ = GND, T A = -40°C to +85°C, unless otherwise noted. Typical values are at V DD = +5V, T A =+25°C.) (Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

SDA, SCL, V DD to GND.........................................-0.3V to +6.0V All Other Pins to GND.................................-0.3V to (V DD + 0.3V)Maximum Continuous Current into H_, L_, and W_

MAX5477......................................................................±5.0mA MAX5478......................................................................±1.3mA MAX5479......................................................................±0.6mA

Continuous Power Dissipation (T A = +70°C)

16-Pin Thin QFN (derate 17.5mW/°C above +70°C) 1399mW 14-Pin TSSOP (derate 9.1mW/°C above +70°C).........727mW Operating Temperature Range ...........................-40°C to +85°C Maximum Junction Temperature.....................................+150°C Storage Temperature Range.............................-65°C to +150°C Lead Temperature (soldering, 10s).................................+300°C

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

_______________________________________________________________________________________3

ELECTRICAL CHARACTERISTICS (continued)

TIMING CHARACTERISTICS

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers 4_______________________________________________________________________________________

Note 1:All devices are production tested at T A = +25°C and are guaranteed by design and characterization for -40°C < T A < +85°C.Note 2:The DNL and INL are measured with the potentiometer configured as a voltage-divider with H_ = V DD and L_ = GND. The

wiper terminal is unloaded and measured with a high-input-impedance voltmeter.

Note 3:The DNL and INL are measured with the potentiometer configured as a variable resistor. H_ is unconnected and L_ =

GND. For V DD = +5V, the wiper is driven with 400μA (MAX5477), 80μA (MAX5478), or 40μA (MAX5479). For V DD = +3V,the wiper is driven with 200μA (MAX5477), 40μA (MAX5478), or 20μA (MAX5479).

Note 4:The wiper resistance is measured using the source currents given in Note 3.

Note 5:The devices draw current in excess of the specified supply current when the digital inputs are driven with voltages between

(V DD - 0.5V) and (GND + 0.5V). See Supply Current vs. Digital Input Voltage in the Typical Operating Characteristics .

Note 6:Wiper at midscale with a 10pF load (DC measurement). L_ = GND, an AC source is applied to H_, and the W_ output is

measured. A 3dB bandwidth occurs when the AC W_/H_ value is 3dB lower than the DC W_/H_ value.

Note 7:The programming current exists only during power-up and EEPROM writes.

Note 8:The SCL clock period includes rise and fall times (t R = t F ). All digital input signals are specified with t R = t F = 2ns and

timed from a voltage level of (V IL + V IH ) / 2.

Note 9:Digital timing is guaranteed by design and characterization, and is not production tested.

Note 10:This is measured from the STOP pulse to the time it takes the output to reach 50% of the output step size (divider mode).It

is measured with a maximum external capacitive load of 10pF.

Note 11:An appropriate bus pullup resistance must be selected depending on board capacitance. Refer to the I 2C-bus specifica-tion document linked to this web address: https://www.wendangku.net/doc/e310837606.html,/acrobat/literature/9398/39340011.pdf

Note 12:The idle time begins from the initiation of the STOP pulse.

TIMING CHARACTERISTICS (continued)

(V = +2.7V to +5.25V, H_ = V , L_ = G ND, T = -40°C to +85°C, unless otherwise noted. Typical values are at V = +5V,

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

_______________________________________________________________________________________5

SUPPLY CURRENT vs. TEMPERATURE

TEMPERATURE (°C)

S U P P L Y C U R R E N T (μA )

-15

0.10.20.30.40.50.60.70.80.91.00-40

0100502001503002503504504005000

128160192224256

WIPER RESISTANCE vs. INPUT CODE

M A X 5477/78/79 t o c 02

INPUT CODE

W I P E R R E S I S T A N C E (?)

TAP-TO-TAP SWITCHING TRANSIENT

1μs/div

SDA 2V/div

20mV/div

MAX5478C L = 10pF H_ = V DD

FROM TAP 00 TO TAP 04

TAP-TO-TAP SWITCHING TRANSIENT

MAX5477/78/79 toc04

400ns/div

SDA 2V/div

20mV/div

MAX5479C W_ = 10pF H_ = V DD

FROM TAP 00 TO TAP 04WIPER TRANSIENT AT POWER-ON

MAX5477/78/79 toc05

μs/div

V DD 2V/div W_1V/div

MAX5478TAP = 128

WIPER TRANSIENT AT POWER-ON

2μs/div

V DD 2V/div

W_1V/div

MAX5479TAP = 128

-0.3

-0.2-0.100.10.20.3

128160192224256INTEGRAL NONLINEARITY vs. CODE (VDM MODE)

CODE

I N L (L S B )

-0.3

-0.2-0.100.10.20.3

0643296128160192224256DIFFERENTIAL NONLINEARITY vs. CODE (VDM MODE)

CODE

D N L (L S B )

-0.3

-0.2-0.100.10.20.3

0643296128160192224256INTEGRAL NONLINEARITY vs. CODE (VRM MODE)

CODE

I N L (L S B )

Typical Operating Characteristics

(V DD = +5V, H_ = V DD , L_ = GND, T A = +25°C, unless otherwise noted.)

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers 6_______________________________________________________________________________________

-0.10

-0.08-0.0400.020.060.10

643296128160192224256DIFFERENTIAL NONLINEARITY vs. CODE (VRM MODE)

CODE

D N L (L S B )

-0.06-0.020.080.04-0.20

-0.12-0.16-0.04-0.080.0400.080.160.120.20

0649632128160192

224256INTEGRAL NONLINEARITY vs. CODE (VDM MODE)

CODE

I N L (L S B )-0.14

-0.02-0.04-0.06-0.08-0.10-0.1200.040.020.100.080.120.060.140643296128160

192224256DIFFERENTIAL NONLINEARITY vs. CODE (VDM MODE)

CODE

D N L (L S B )

-0.20

-0.12-0.16-0.04-0.080.0400.080.160.120.200

649632128160192

224256INTEGRAL NONLINEARITY vs. CODE (VRM MODE)

CODE

I N L (L S B )-0.20

-0.12-0.16

-0.04-0.080.0400.080.160.120.20

128160192

224256DIFFERENTIAL NONLINEARITY vs. CODE (VRM MODE)

CODE

D N L (L S B )CROSSTALK vs. FREQUENCY (MAX5478)

FREQUENCY (kHz)

C R O S S T A L K (d B )

100

0.1

-90-80-70-60-50-40-30-20-100-100

0.01

1000

CROSSTALK vs. FREQUENCY (MAX5479)

FREQUENCY (kHz)

C R O S S T A L K (d B )

1000

100

-90-80-70-60-50-40-30-20-100

-100

0.1

10,000

Typical Operating Characteristics (continued)

(V DD = +5V, H_ = V DD , L_ = GND, T A = +25°C, unless otherwise noted.)

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

_______________________________________________________________________________________7

MIDSCALE WIPER RESPONSE vs. FREQUENCY (MAX5478)

FREQUENCY (kHz)

G A I N (d B )

100

101

-7-6-5-4-3-2-1012-80.1

1000

MIDSCALE WIPER RESPONSE vs. FREQUENCY (MAX5479)

FREQUENCY (kHz)

G A I N (d B )

100101

-4

-3-2-1012-5

0.1

1000

THD+N vs. FREQUENCY

(MAX5478)

FREQUENCY (kHz)

T H D +N (%)

0.1

0.0010.010.11

0.0001

0.01

100

THD+N vs. FREQUENCY

(MAX5479)

FREQUENCY (kHz)

T H D +N (%)

0.1

0.001

0.01

0.1

0.0001

0.01

100

-0.5

-0.2-0.3-0.4-0.100.10.20.30.40.5-40

-15

85END-TO-END RESISTANCE % CHANGE vs. TEMPERATURE (MAX5478)

M A X 5477/78/79 t o c 21

TEMPERATURE (°C)E N D -T O -E N D R E S I S T A N C E C H A N G E (%)

-0.5

-0.2-0.3-0.4-0.100.10.20.30.40.5-40

-15

85END-TO-END RESISTANCE % CHANGE vs. TEMPERATURE (MAX5479)

M A X 5477/78/79 t o c 22

TEMPERATURE (°C)

E N D -T O -E N D R E S I S T A N C E C H A N G E (%)

350300250400450

550500600

0 1.00.5 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

SUPPLY CURRENT vs. DIGITAL INPUT VOLTAGE

DIGITAL INPUT VOLTAGE (V)

S U P P L Y C U R R E N T (μA )

20015010050Typical Operating Characteristics (continued)

(V DD = +5V, H_ = V DD , L_ = GND, T A = +25°C, unless otherwise noted.)

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers 8_______________________________________________________________________________________

Detailed Description

The MAX5477/MAX5478/MAX5479 contain two resistor arrays with 255 elements in each array. The MAX5477has a total end-to-end resistance of 10k ?, the MAX5478 has an end-to-end resistance of 50k ?, and the MAX5479 has an end-to-end resistance of 100k ?.

The MAX5477/MAX5478/MAX5479 provide access to the high, low, and wiper terminals for a standard volt-age-divider configuration. Connect H_, L_, and W_ in any desired configuration as long as their voltages remain between GND and V DD .

Figure 1. I 2C Serial-Interface Timing Diagram

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

_______________________________________________________________________________________

A simple 2-wire I 2C-compatible serial interface moves the wiper among the 256 tap points (Figure 2). A non-volatile memory stores the wiper position and recalls the stored wiper position upon power-up. The non-volatile memory is guaranteed for 50 years for wiper data retention and up to 200,000 wiper store cycles.

Analog Circuitry

The MAX5477/MAX5478/MAX5479 consist of two resistor arrays with 255 resistive elements; 256 tap points are accessible to the wipers, along the resistor string between H_ and L_. The wiper tap point is selected by programming the potentiometer through the I 2C inter-face. An address byte, a command byte, and 8 data bits program the wiper position for each potentiometer. The H_ and L_ terminals of the MAX5477/MAX5478/MAX5479 are similar to the two end terminals of a mechanical potentiometer. The MAX5477/MAX5478/MAX5479 feature power-on reset circuitry that loads the wiper position from the nonvolatile memory at power-up.

Digital Interface

The MAX5477/MAX5478/MAX5479 feature an internal,nonvolatile EEPROM that stores the wiper state for ini-tialization during power-up. The shift register decodes the command and address bytes, routing the data to the proper memory registers. Data written to a volatile memory register immediately updates the wiper posi-tion, or writes data to a nonvolatile register for storage (see Table 2).

The volatile register retains data as long as the device is powered. Removing power clears the volatile regis-ter. The nonvolatile register retains data even after power is removed. Upon power-up, the power-on reset circuitry controls the transfer of data from the non-volatile register to the volatile register.

A write-protect feature prevents accidental overwriting of the EEPROM. Connect WP to V DD or leave open to prevent any EEPROM write cycles. The wiper register only updates with the value in the EEPROM when WP =

Figure 3. Start and Stop Conditions

Figure 2. Potentiometer Configuration

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers 10

______________________________________________________________________________________

the EEPROM and to update the wiper position from either the value in the EEPROM or directly from the I 2C interface. Connecting WP to GND increases the supply current by 19.6μA (max).

Serial Addressing

The MAX5477/MAX5478/MAX5479 operate as slave devices that send and receive data through an I 2C-/SMBus?-compatible 2-wire serial interface. The inter-face uses a serial data access (SDA) line and a serial clock line (SCL) to achieve bidirectional communication between master(s) and slave(s). A master, typically a microcontroller, initiates all data transfers to the

MAX5477/MAX5478/MAX5479, and generates the SCL clock that synchronizes the data transfer (Figure 1).

The MAX5477/MAX5478/MAX5479 SDA line operates as both an input and an open-drain output. The SDA line requires a pullup resistor, typically 4.7k ?. The MAX5477/MAX5478/MAX5479 SCL line operates only as an input. The SCL line requires a pullup resistor (typ-ically 4.7k ?) if there are multiple masters on the 2-wire

interface, or if the master in a single-master system has an open-drain SCL output. SCL and SDA should not exceed V DD in a mixed-voltage system, despite the open-drain drivers.

Each transmission consists of a START (S) condition (Figure 3) sent by a master, followed by the MAX5477/MAX5478/MAX5479 7-bit slave address plus the NOP/W bit (Figure 4), 1 command byte and 1 data byte, and finally a STOP (P) condition (Figure 3).Start and Stop Conditions

Both SCL and SDA remain high when the interface is not busy. A master controller signals the beginning of a transmission with a START condition by transitioning SDA from high to low while SCL is high. The master controller issues a STOP condition by transitioning the SDA from low to high while SCL is high, when it finishes communicating with the slave. The bus is then free for another transmission (Figure 3).

Bit Transfer

One data bit is transferred during each clock pulse.The data on the SDA line must remain stable while SCL is high (Figure 5).

Acknowledge

The acknowledge bit is a clocked 9th bit that the recipient uses to handshake receipt of each byte of data (Figure 6). Thus, each byte transferred effectively requires 9 bits.The master controller generates the 9th clock pulse, and the recipient pulls down SDA during the acknowledge clock pulse, so the SDA line remains stable low during the high period of the clock pulse.

Slave Address

The MAX5477/MAX5478/MAX5479 have a 7-bit-long slave address (Figure 4). The 8th bit following the 7-bit

Figure 5. Bit Transfer

Figure 6. Acknowledge

SMBus is a trademark of Intel Corporation.

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

______________________________________________________________________________________11

slave address is the NOP/W bit. Set the NOP/W bit low for a write command and high for a no-operation command.The MAX5477/MAX5478/MAX5479 provide three address inputs (A0, A1, and A2), allowing up to eight devices to share a common bus (Table 1). The first 4bits (MSBs) of the MAX5477/MAX5478/MAX5479 slave addresses are always 0101. A2, A1, and A0 set the next 3 bits in the slave address. Connect each address input to V DD or G ND to set these 3 bits. Each device must have a unique address to share a common bus.

Message Format for Writing

Write to the MAX5477/MAX5478/MAX5479 by transmit-ting the device’s slave address with NOP/W (8th bit) set to zero, followed by at least 1 byte of information (Figure 7). The 1st byte of information is the command byte. The bytes received after the command byte are the data bytes. The 1st data byte goes into the internal register of the MAX5477/MAX5478/MAX5479 as select-ed by the command byte (Figure 8).

Command Byte

Use the command byte to select the source and desti-nation of the wiper data (nonvolatile or volatile memory registers) and swap data between nonvolatile and volatile memory registers (see Table 2).

Command Descriptions

VREG: The data byte writes to the volatile memory reg-ister and the wiper position updates with the data in the volatile memory register.

NVREG: The data byte writes to the nonvolatile memory register. The wiper position is unchanged.

NVREG xVREG : Data transfers from the nonvolatile memory register to the volatile memory register (wiper position updates).

VREGxNVREG: Data transfers from the volatile memory register into the nonvolatile memory register.

Nonvolatile Memory

The internal EEPROM consists of a 16-bit nonvolatile register that retains the value written to it prior to power down. The nonvolatile register is programmed with the midscale value at the factory. The nonvolatile memory is guaranteed for 50 years for wiper position retention and up to 200,000 wiper write cycles. A write-protect feature prevents accidental overwriting of the EEPROM.Connect WP to V DD or leave open to enable the write-protect feature. The wiper position only updates with the value in the EEPROM when WP = V DD . Connect WP to G ND to allow EEPROM write cycles and to update the wiper position from nonvolatile memory or directly from the I 2C serial interface.

Power-Up

Upon power-up, the MAX5477/MAX5478/MAX5479load the data stored in the nonvolatile memory register into the volatile memory register, updating the wiper position with the data stored in the nonvolatile memory register. This initialization period takes 10μs.

Figure 7. Command Byte Received

Figure 8. Command and Single Data Byte Received

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers 12

______________________________________________________________________________________

Table 2. Command Byte Summary

The MAX5477/MAX5478/MAX5479 feature a low-power standby mode. When the device is not being pro-grammed, it enters into standby mode and supply cur-rent drops to 500nA (typ).

Applications Information

The MAX5477/MAX5478/MAX5479 are ideal for circuits requiring digitally controlled adjustable resistance,such as LCD contrast control (where voltage biasing adjusts the display contrast), or for programmable fil-ters with adjustable gain and/or cutoff frequency.

Positive LCD Bias Control

Figures 9 and 10 show an application where the MAX5477/MAX5478/MAX5479 provide an adjustable,positive LCD bias voltage. The op amp provides buffer-

the potentiometer (Figure 9) or by a fixed resistor and a variable resistor (see Figure 10).

Programmable Filter

Figure 11 shows the MAX5477/MAX5478/MAX5479 in a 1st-order programmable application filter. Adjust the gain of the filter with R 2, and set the cutoff frequency with R 3. Use the following equations to calculate the gain (A) and the -3dB cutoff frequency (f C ):

Figure 9. Positive LCD Bias Control Using a Voltage-Divider Figure 10. Positive LCD Bias Control Using a Variable Resistor

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

Connect the high and low terminals of one potentiome-ter of a MAX5477 between the NULL inputs of a MAX410 and the wiper to the op amp’s positive supply to nullify the offset voltage over the operating tempera-ture range. Install the other potentiometer in the feed-back path to adjust the gain of the MAX410 (Figure 12).

Adjustable Voltage Reference

Figure 13 shows the MAX5477/MAX5478/MAX5479used as the feedback resistors in multiple adjustable voltage reference applications. Independently adjust the output voltages of the MAX6160 parts from 1.23V to V IN - 0.2V by changing the wiper positions of the MAX5477/MAX5478/MAX5479.

Figure 12. Offset Voltage Adjustment Circuit

Pin Configurations

Chip Information

TRANSISTOR COUNT: 12,651PROCESS: BiCMOS

M A X 5477/M A X 5478/M A X 5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface, Digital Potentiometers 14______________________________________________________________________________________

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to https://www.wendangku.net/doc/e310837606.html,/packages .)

MAX5477/MAX5478/MAX5479

Dual, 256-Tap, Nonvolatile, I 2C-Interface,

Digital Potentiometers

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.

15____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600?2004 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to https://www.wendangku.net/doc/e310837606.html,/packages .)