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256-Position Two-Time Programmable I2C Digital Potentiometer AD5170
FEATURES
256-position TTP (two-time programmable) set-and-forget resistance setting allows second-chance permanent programming Unlimited adjustments prior to OTP (one-time programming) activation OTP overwrite allows dynamic adjustments with user defined preset End-to-end resistance: 2.5 k, 10 k, 50 k, 100 k Compact MSOP-10 (3 mm x 4.9 mm) package Fast settling time: tS = 5 s typ in power-up Full read/write of wiper register Power-on preset to midscale Extra package address decode pins AD0 and AD1 Single-supply 2.7 V to 5.5 V Low temperature coefficient: 35 ppm/C Low power, IDD = 6 A maximum Wide operating temperature: -40C to +125C Evaluation board and software are available Software replaces C in factory programming applications
FUNCTIONAL BLOCK DIAGRAM
A W B
VDD 1 GND
FUSE LINKS
2
RDAC REGISTER
AD0 AD1 SDA SCL
ADDRESS DECODE
/8
SERIAL INPUT REGISTER
04104-0-001
Figure 1.
APPLICATIONS
Systems calibration Electronics level setting Mechanical Trimmers(R) replacement in new designs Permanent factory PCB setting Transducer adjustment of pressure, temperature, position, chemical, and optical sensors RF amplifier biasing Automotive electronics adjustment Gain control and offset adjustment
The AD5170 is programmed using a 2-wire, I2C(R) compatible digital interface. Unlimited adjustments are allowed before permanently (there are actually two opportunities) setting the resistance value. During OTP activation, a permanent blow fuse command freezes the wiper position (analogous to placing epoxy on a mechanical trimmer). Unlike traditional OTP digital potentiometers, the AD5170 has a unique temporary OTP overwrite feature that allows for new adjustments even after the fuse has been blown. However, the OTP setting is restored during subsequent power-up conditions. This feature allows users to treat these digital potentiometers as volatile potentiometers with a programmable preset. For applications that program the AD5170 at the factory, Analog Devices offers device programming software running on Windows NT(R), 2000, and XP(R) operating systems. This software effectively replaces any external I2C controllers, thus enhancing the time-to-market of the user's systems.
1
GENERAL OVERVIEW
The AD5170 is a 256-position, two-time programmable (TTP) digital potentiometer1 that employs fuse link technology to enable two opportunities at permanently programming the resistance setting. OTP is a cost-effective alternative to EEMEM for users who do not need to program the digital potentiometer setting in memory more than once. This device performs the same electronic adjustment function as mechanical potentiometers or variable resistors with enhanced resolution, solid-state reliability, and superior low temperature coefficient performance.
The terms digital potentiometer, VR, and RDAC are used interchangeably.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
AD5170 TABLE OF CONTENTS
Electrical Characteristics -- 2.5 k ............................................... 3 Electrical Characteristics -- 10 k, 50 k, 100 k Versions..... 4 Timing Characteristics -- 2.5 k, 10 k, 50 k, 100 k Versions.............................................................................................. 5 Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Typical Performance Characteristics ............................................. 7 Test Circuits..................................................................................... 11 Theory of Operation ...................................................................... 12 One-Time Programming (OTP) .............................................. 12 Programming the Variable Resistor and Voltage ................... 12 Programming the Potentiometer Divider ............................... 13 ESD Protection ........................................................................... 14 Terminal Voltage Operating Range ......................................... 14 Power-Up Sequence ................................................................... 14 Power Supply Considerations................................................... 14 Layout Considerations............................................................... 15 Evaluation Software/Hardware..................................................... 16 Software Programming ............................................................. 16 I2C Interface .................................................................................... 18 I2C Compatible 2-Wire Serial Bus ........................................... 20 Pin Configuration and Function Descriptions........................... 22 Outline Dimensions ....................................................................... 23 Ordering Guide .......................................................................... 23
REVISION HISTORY
11/04--Data Sheet Changed from Rev. 0 to Rev. A Changes to Electrical Characteristics Table 1 ............................... 3 Changes to Electrical Characteristics Table 2 ............................... 4 Changes to One-Time Programming ......................................... 12 Changes to Figure 37, Figure 38, and Figure 39 ........................ 14 Changes to Power Supply Considerations................................... 14 Changes to Figure 40...................................................................... 15 Changes to Layout Considerations .............................................. 15 11/03--Revision 0: Initial Version
Rev. A | Page 2 of 24
AD5170 ELECTRICAL CHARACTERISTICS -- 2.5 k
VDD = 5 V 10% or 3 V 10%, VA = +VDD, VB = 0 V, -40C < TA < +125C, unless otherwise noted. Table 1.
Parameter Symbol Conditions DC CHARACTERISTICS--RHEOSTAT MODE Resistor Differential Nonlinearity2 R-DNL RWB, VA = no connect Resistor Integral Nonlinearity2 R-INL RWB, VA = no connect Nominal Resistor Tolerance3 RAB TA = 25C Resistance Temperature Coefficient (RAB/RAB)/T VAB = VDD, Wiper = no connect RWB (Wiper Resistance) RWB Code = 0x00, VDD = 5 V DC CHARACTERISTICS -- POTENTIOMETER DIVIDER MODE (Specifications apply to all VRs) Differential Nonlinearity4 DNL Integral Nonlinearity4 INL Voltage Divider Temperature Coefficient (VW/VW)/T Code = 0x80 Full-Scale Error VWFSE Code = 0xFF Zero-Scale Error VWZSE Code = 0x00 RESISTOR TERMINALS Voltage Range5 VA,VB,VW Capacitance6 A, B CA, CB f = 1 MHz, measured to GND, code = 0x80 Capacitance W CW f = 1 MHz, measured to GND, code = 0x80 Shutdown Supply Current7 IA_SD VDD = 5.5 V Common-Mode Leakage ICM VA = VB = VDD/2 DIGITAL INPUTS AND OUTPUTS Input Logic High VIH VDD = 5 V Input Logic Low VIL VDD = 5 V Input Logic High VIH VDD = 3 V Input Logic Low VIL VDD = 3 V Input Current IIL VIN = 0 V or 5 V Input Capacitance5 CIL POWER SUPPLIES Power Supply Range VDD RANGE OTP Supply Voltage VDD_OTP TA = 25C Supply Current IDD VIH = 5 V or VIL = 0 V OTP Supply Current IDD_OTP VDD_OTP = 5.5 V, TA = 25C Power Dissipation8 PDISS VIH = 5 V or VIL = 0 V, VDD = 5 V Power Supply Sensitivity PSS VDD = 5 V 10%, Code = midscale 9 DYNAMIC CHARACTERISTICS Bandwidth -3 dB BW_2.5K Code = 0x80 Total Harmonic Distortion THDW VA = 1 V rms, VB = 0 V, f = 1 kHz VW Settling Time tS VA = 5 V, VB = 0 V, 1 LSB error band Resistor Noise Voltage Density eN_WB RWB = 1.25 k, RS = 0
1 2
Min -2 -6 -20
Typ1 0.1 0.75 35 160
Max +2 +6 +55 200 +1.5 +2 0 10 VDD
Unit LSB LSB % ppm/C LSB LSB ppm/C LSB LSB V pF pF A nA V V V V A pF V V A mA W %/% MHz % s nV/Hz
-1.5 -2 -10 0 GND
0.1 0.6 15 -2.5 2
45 60 0.01 1 2.4
1
0.8 2.1 0.6 1 5 2.7 5.25 3.5 100 0.02 4.8 0.1 1 3.2 30 0.08 5.5 5.5 6
Typical specifications represent average readings at 25C and VDD = 5 V. Resistor position nonlinearity error, R-INL, is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. 3 VAB = VDD, Wiper (VW) = no connect. 4 INL and DNL are measured at VW with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. VA = VDD and VB = 0 V. DNL specification limits of 1 LSB maximum are guaranteed monotonic operating conditions. 5 Resistor terminals A, B, W have no limitations on polarity with respect to each other. 6 Guaranteed by design and not subject to production test. 7 Measured at the A terminal. The A terminal is open circuited in shutdown mode. 8 PDISS is calculated from (IDD x VDD). CMOS logic level inputs result in minimum power dissipation. 9 All dynamic characteristics use VDD = 5 V.
Rev. A | Page 3 of 24
AD5170 ELECTRICAL CHARACTERISTICS -- 10 k, 50 k, 100 k VERSIONS
VDD = 5 V 10% or 3 V 10%, VA = VDD; VB = 0 V, -40C < TA < +125C, unless otherwise noted. Table 2.
Parameter Symbol Conditions DC CHARACTERISTICS--RHEOSTAT MODE Resistor Differential Nonlinearity2 R-DNL RWB, VA = no connect R-INL RWB, VA = no connect Resistor Integral Nonlinearity2 Nominal Resistor Tolerance3 RAB TA = 25C Resistance Temperature Coefficient (RAB/RAB)/T VAB = VDD, wiper = no connect RWB (Wiper Resistance) RWB Code = 0x00, VDD = 5 V DC CHARACTERISTICS -- POTENTIOMETER DIVIDER MODE (Specifications apply to all VRs) Differential Nonlinearity4 DNL INL Integral Nonlinearity4 Code = 0x80 Voltage Divider Temperature (VW/VW)/T Coefficient Full-Scale Error VWFSE Code = 0xFF Zero-Scale Error VWZSE Code = 0x00 RESISTOR TERMINALS Voltage Range5 VA,VB,VW Capacitance6 A, B f = 1 MHz, measured to GND, code = 0x80 CA, CB CW f = 1 MHz, measured to GND, code = 0x80 Capacitance6 W Shutdown Supply Current7 IA_SD VDD = 5.5 V Common-Mode Leakage ICM VA = VB = VDD/2 DIGITAL INPUTS AND OUTPUTS Input Logic High VIH VDD = 5 V Input Logic Low VIL VDD = 5 V Input Logic High VIH VDD = 3 V Input Logic Low VIL VDD = 3 V Input Current IIL VIN = 0 V or 5 V CIL Input Capacitance6 POWER SUPPLIES Power Supply Range VDD RANGE OTP Supply Voltage8 VDD_OTP Supply Current IDD VIH = 5 V or VIL = 0 V OTP Supply Current9 IDD_OTP VDD_OTP = 5.5 V, TA = 25C Power Dissipation10 PDISS VIH = 5 V or VIL = 0 V, VDD = 5 V Power Supply Sensitivity PSS VDD = 5 V 10%, code = midscale DYNAMIC CHARACTERISTICS11 Bandwidth -3 dB BW RAB = 10 k, code = 0x80 RAB = 50 k, code = 0x80 RAB = 100 k, code = 0x80 Total Harmonic Distortion THDW VA =1 V rms, VB = 0 V, f = 1 kHz, RAB = 10 k VW Settling Time tS VA = 5 V, VB = 0 V, 1 LSB error band (10 k/50 k/100 k) Resistor Noise Voltage Density eN_WB RWB = 5 k, RS = 0
1 2
Min -1 -2.5 -20
Typ1 0.1 0.25 35 160
Max +1 +2.5 +20 200 +1 +1
Unit LSB LSB % ppm/C LSB LSB ppm/C LSB LSB V pF pF A nA V V V V A pF V V A mA W %/% kHz kHz kHz % s nV/Hz
-1 -1
0.1 0.3 15 -1 1
-2.5 0 GND
0 2.5 VDD
45 60 0.01 1 2.4
1
0.8 2.1 0.6 1 5 2.7 5.25 3.5 100 0.02 600 100 40 0.1 2 9 30 0.08 5.5 5.5 6
Typical specifications represent average readings at 25C and VDD = 5 V. Resistor position nonlinearity error, R-INL, is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. 3 VAB = VDD, Wiper (VW) = no connect. 4 INL and DNL are measured at VW with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. VA = VDD and VB = 0 V. DNL specification limits of 1 LSB maximum are guaranteed monotonic operating conditions. 5 Resistor terminals A, B, W have no limitations on polarity with respect to each other. 6 Guaranteed by design and not subject to production test. 7 Measured at the A terminal. The A terminal is open circuited in shutdown mode. 8 Different from operating power supply, power supply OTP is used one time only. 9 Different from operating current, supply current for OTP lasts approximately 400 ms for one time only. 10 PDISS is calculated from (IDD x VDD). CMOS logic level inputs result in minimum power dissipation. 11 All dynamic characteristics use VDD = 5 V.
Rev. A | Page 4 of 24
AD5170 TIMING CHARACTERISTICS -- 2.5 k, 10 k, 50 k, 100 k VERSIONS
VDD = 5 V 10% or 3 V 10%, VA = VDD; VB = 0 V, -40C < TA < +125C, unless otherwise noted. Table 3.
Parameter Symbol Conditions I2C INTERFACE TIMING CHARACTERISTICS1 (Specifications apply to all parts) SCL Clock Frequency fSCL tBUF Bus Free Time between STOP and START t1 tHD;STA Hold Time (Repeated START) t2 After this period, the first clock pulse is generated. tLOW Low Period of SCL Clock t3 tHIGH High Period of SCL Clock t4 tSU;STA Setup Time for Repeated START Condition t5 tHD;DAT Data Hold Time2 t6 tSU;DAT Data Setup Time t7 tF Fall Time of Both SDA and SCL Signals t8 tR Rise Time of Both SDA and SCL Signals t9 tSU;STO Setup Time for STOP Condition t10
1 2
Min
Typ
Max 400
Unit kHz s s s s s s ns ns ns s
1.3 0.6 1.3 0.6 0.6 0.9 100 300 300 0.6
See timing diagrams for locations of measured values. The maximum tHD;DAT has only to be met if the device does not stretch the LOW period (tLOW) of the SCL signal.
Rev. A | Page 5 of 24
AD5170 ABSOLUTE MAXIMUM RATINGS
TA = 25C, unless otherwise noted. Table 4.
Parameter VDD to GND VA, VB, VW to GND Terminal Current, Ax-Bx, Ax-Wx, Bx-Wx1 Pulsed Continuous Digital Inputs and Output Voltage to GND Operating Temperature Range Maximum Junction Temperature (TJMAX) Storage Temperature Lead Temperature (Soldering, 10 sec) Thermal Resistance2 JA: MSOP-10 Value -0.3 V to +7 V VDD 20 mA 5 mA 0 V to 7 V -40C to +125C 150C -65C to +150C 300C 230C/W
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
1
Maximum terminal current is bound by the maximum current handling of the switches, maximum power dissipation of the package, and maximum applied voltage across any two of the A, B, and W terminals at a given resistance. 2 Package power dissipation = (TJMAX - TA)/JA.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. A | Page 6 of 24
AD5170 TYPICAL PERFORMANCE CHARACTERISTICS
2.0 1.5
RHEOSTAT MODE INL (LSB)
0.5
TA = 25C RAB = 10k
POTENTIOMETER MODE DNL (LSB)
0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4
04104-0-002
RAB = 10k
1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 0 32 64
VDD = 2.7V
VDD = 2.7V; TA = -40C, +25C, +85C, +125C
VDD = 5.5V
96
128
160
192
224
256
0
32
64
96
128
160
192
224
256
CODE (DECIMAL)
CODE (DECIMAL)
Figure 2. R-INL vs. Code vs. Supply Voltages
Figure 5. DNL vs. Code vs. Temperature
0.5 0.4 TA = 25C RAB = 10k
1.0 0.8 TA = 25C RAB = 10k
RHEOSTAT MODE DNL (LSB)
0.3 0.2 VDD = 2.7V 0.1 0 -0.1 -0.2 -0.3 -0.4
04104-0-003
POTENTIOMETER MODE INL (LSB)
0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 VDD = 2.7V VDD = 5.5V
VDD = 5.5V
0
32
64
96
128
160
192
224
256
0
32
64
96
128
160
192
224
256
CODE (DECIMAL)
CODE (DECIMAL)
Figure 3. R-DNL vs. Code vs. Supply Voltages
Figure 6. INL vs. Code vs. Supply Voltages
0.5 0.4 RAB = 10k
0.5 0.4 TA = 25C RAB = 10k
0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4
POTENTIOMETER MODE DNL (LSB)
POTENTIOMETER MODE INL (LSB)
VDD = 5.5V TA = -40C, +25C, +85C, +125C
0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 VDD = 5.5V VDD = 2.7V
VDD = 2.7V TA = -40C, +25C, +85C, +125C
04104-0-004
0
32
64
96
128
160
192
224
256
0
32
64
96
128
160
192
224
256
CODE (DECIMAL)
CODE (DECIMAL)
Figure 4. INL vs. Code vs. Temperature
Figure 7. DNL vs. Code vs. Supply Voltages
Rev. A | Page 7 of 24
04104-0-007
-0.5
-0.5
04104-0-006
-0.5
-1.0
04104-0-005
-0.5
AD5170
2.0 RAB = 10k 1.5 VDD = 2.7V TA = -40C, +25C, +85C, +125C 4.50 RAB = 10k
1.0 0.5 0 -0.5 -1.0 -1.5
04104-0-008
ZSE, ZERO-SCALE ERROR (LSB)
3.75
RHEOSTAT MODE INL (LSB)
3.00
2.25
VDD = 2.7V, VA = 2.7V
VDD = 5.5V TA = -40C, +25C, +85C, +125C
1.50 VDD = 5.5V, VA = 5.0V 0.75
0
32
64
96
128
160
192
224
256
-25
-10
5
20
35
50
65
80
95
110
125
CODE (DECIMAL)
TEMPERATURE (C)
Figure 8. R-INL vs. Code vs. Temperature
Figure 11. Zero-Scale Error vs. Temperature
0.5 0.4 RAB = 10k
10
RHEOSTAT MODE DNL (LSB)
0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 0 32 64 96 128 160 192 224 256
04104-0-009
VDD = 2.7V, 5.5V; TA = -40C, +25C, +85C, +125C
IDD, SUPPLY CURRENT (A)
VDD = 5V
1 VDD = 3V
-7
26
59
92
125
CODE (DECIMAL)
TEMPERATURE (C)
Figure 9. R-DNL vs. Code vs. Temperature
Figure 12. Supply Current vs. Temperature
2.0 RAB = 10k
120 RAB = 10k
1.0 0.5 0 -0.5 -1.0 -1.5
04104-0-010
RHEOSTAT MODE TEMPCO (ppm/C)
1.5
100
FSE, FULL-SCALE ERROR (LSB)
80 60 VDD = 2.7V TA = -40C TO +85C, -40C TO +125C VDD = 5.5V TA = -40C TO +85C, -40C TO +125C
VDD = 5.5V, VA = 5.0V
40
VDD = 2.7V, VA = 2.7V
20
0 -20 0 32 64 96 128 160 192 224 256 CODE (DECIMAL)
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (C)
Figure 10. Full-Scale Error vs. Temperature
Figure 13. Rheostat Mode Tempco RWB/T vs. Code
Rev. A | Page 8 of 24
04104-0-013
-2.0 -40
04104-0-012
-0.5
0.1 -40
04104-0-011
-2.0
0 -40
AD5170
50
0
POTENTIOMETER MODE TEMPCO (ppm/C)
RAB = 10k 40 30 20 10 0 -10 -20
04104-0-014
-6 -12
0x80 0x40 0x20 0x10 0x08 0x04 0x02
VDD = 2.7V TA = -40C TO +85C, -40C TO +125C
-18
GAIN (dB)
-24 -30 -36 -42
VDD = 5.5V TA = -40C TO +85C, -40C TO +125C
0x01 -48 -54
0
32
64
96
128
160
192
224
256
1k
10k
100k FREQUENCY (Hz)
1M
CODE (DECIMAL)
Figure 14. Potentiometer Mode Tempco VWB/T vs. Code
Figure 17. Gain vs. Frequency vs. Code, RAB = 50 k
0 -6 -12 -18
GAIN (dB)
0
0x80 0x40 0x20 0x10
GAIN (dB)
-6 -12 -18 -24 -30 -36 -42 -48 -54
04104-0-015
0x80 0x40 0x20 0x10 0x08 0x04 0x02 0x01
-24 -30 -36 -42 -48 -54 -60 10k
0x08 0x04
0x02 0x01
100k FREQUENCY (Hz)
1M
10M
1k
10k
100k FREQUENCY (Hz)
1M
Figure 15. Gain vs. Frequency vs. Code, RAB = 2.5 k
Figure 18. Gain vs. Frequency vs. Code, RAB = 100 k
0 -6 -12 -18 0x80 0x40 0x20 0x10
0 -6 -12 -18 100k 60kHz 50k 120kHz 10k 570kHz 2.5k 2.2MHz
GAIN (dB)
0x08 -30 0x04 -36 -42 -48 -54
04104-0-016
GAIN (dB)
-24
-24 -30 -36 -42 -48 -54
0x02 0x01
1k
10k
100k FREQUENCY (Hz)
1M
1k
10k
100k FREQUENCY (Hz)
1M
10M
Figure 16. Gain vs. Frequency vs. Code, RAB = 10 k
Figure 19. -3 dB Bandwidth at Code = 0x80
Rev. A | Page 9 of 24
04104-0-019
-60
-60
04104-0-018
-60
04104-0-017
-30
-60
AD5170
10 TA = 25C
IDD, SUPPLY CURRENT (mA)
1 VDD = 5.5V
VW
0.1 VDD = 2.7V
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
DIGITAL INPUT VOLTAGE (V)
04104-0-020
Figure 20. IDD vs. Input Voltage
Figure 22. Midscale Glitch, Code 0x80 to 0x7F
VW
VW
SCL
04104-0-021
SCL
04104-0-023
Figure 21. Digital Feedthrough
Figure 23. Large Signal Settling Time
Rev. A | Page 10 of 24
04104-0-025
0.01
AD5170 TEST CIRCUITS
Figure 24 to Figure 29 illustrate the test circuits that define the test conditions used in the product specification tables.
DUT A V+ B W
VDD
04104-0-026
V+ = VDD 1LSB = V+/2N
VA
V+ = VDD 10%
DUT A W B V+
VMS PSRR (dB) = 20 LOG VDD VMS% PSS (%/%) = VDD%
(
)
04104-0-029
VMS
VMS
Figure 24. Test Circuit for Potentiometer Divider Nonlinearity Error (INL, DNL)
Figure 27. Test Circuit for Power Supply Sensitivity (PSS, PSSR)
NO CONNECT DUT AW B
04104-0-027
DUT A W
+15V
IW
OFFSET GND
VIN B AD8610 VOUT
04104-0-030
04104-0-032
VMS
2.5V
-15V
Figure 25. Test Circuit for Resistor Position Nonlinearity Error (Rheostat Operation; R-INL, R-DNL)
DUT A VMS2 B VMS1 W VW
IW = VDD/RNOMINAL
Figure 28. Test Circuit for Gain vs. Frequency
NC DUT VDD A W GND B ICM
04104-0-028
RW = [VMS1 - VMS2]/IW
VCM NC = NO CONNECT
NC
Figure 26. Test Circuit for Wiper Resistance
Figure 29. Test Circuit for Common-Mode Leakage Current
Rev. A | Page 11 of 24
AD5170 THEORY OF OPERATION
A I2C INTERFACE DAC REG. MUX DECODER W
SCL SDA
B COMPARATOR FUSES EN ONE-TIME PROGRAM/TEST CONTROL BLOCK FUSE REG.
Figure 30. Detailed Functional Block Diagram
The AD5170 is a 256-position, digitally controlled variable resistor (VR) that employs fuse link technology to achieve memory retention of resistance setting. An internal power-on preset places the wiper at midscale during power-on. If the OTP function has been activated, the device powers up at the user-defined permanent setting.
PROGRAMMING THE VARIABLE RESISTOR AND VOLTAGE
Rheostat Operation
The nominal resistance of the RDAC between Terminal A and Terminal B is available in 2.5 k, 10 k, 50 k, and 100 k. The nominal resistance (RAB) of the VR has 256 contact points accessed by the wiper terminal, plus the B terminal contact. The 8-bit data in the RDAC latch is decoded to select one of 256 possible settings.
A W A W A W
04103-0-027
ONE-TIME PROGRAMMING (OTP)
Prior to OTP activation, the AD5170 presets to midscale during initial power-on. After the wiper is set at the desired position, the resistance can be permanently set by programming the T bit high along with the proper coding (see Table 7 and Table 8) and one time VDD_OTP. Note that fuse link technology of the AD517x family of digital pots requires VDD_OTP between 5.25 V and 5.5 V to blow the fuses to achieve a given nonvolatile setting. On the other hand, VDD can be 2.7 V to 5.5 V during operation. As a result, system supply that is lower than 5.25 V requires external supply for one-time programming. Note that the user is allowed only one attempt in blowing the fuses. If the user fails to blow the fuses at the first attempt, the fuses' structures may have changed such that they may never be blown regardless of the energy applied at subsequent events. For details, see the Power Supply Considerations section. The device control circuit has two validation bits, E1 and E0, that can be read back to check the programming status (see Table 7). Users should always read back the validation bits to ensure that the fuses are properly blown. After the fuses have been blown, all fuse latches are enabled upon subsequent power-on; therefore, the output corresponds to the stored setting. Figure 30 shows a detailed functional block diagram.
B
B
04103-0-026
B
Figure 31. Rheostat Mode Configuration
Assuming a 10 k part is used, the wiper's first connection starts at the B terminal for data 0x00. Because there is a 50 wiper contact resistance, such a connection yields a minimum of 100 (2 x 50 ) resistance between Terminal W and Terminal B. The second connection is the first tap point, which corresponds to 139 (RWB = RAB/256 + 2 x RW = 39 + 2 x 50 ) for data 0x01. The third connection is the next tap point, representing 178 (2 x 39 + 2 x 50 ) for data 0x02, and so on. Each LSB data value increase moves the wiper up the resistor ladder until the last tap point is reached at 10,100 (RAB + 2 x RW).
Rev. A | Page 12 of 24
AD5170
A SD BIT RS
For RAB = 10 k and the B terminal open-circuited, the following output resistance, RWA, is set for the RDAC latch codes, as shown in Table 6. Table 6. Codes and Corresponding RWA Resistance
D (Dec.) 255 128 1 0 RWA () 139 5,060 9,961 10,060 Output State Full Scale Midscale 1 LSB Zero Scale
D7 D6 D5 D4 D3 D2 D1 D0
RS
RS W
RDAC
04104-0-034
LATCH AND DECODER
RS B
Typical device-to-device matching is process lot dependent and may vary by up to 30%. Since the resistance element is processed using thin film technology, the change in RAB with temperature has a very low 35 ppm/C temperature coefficient.
PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates a voltage divider at wiper-to-B and wiper-to-A proportional to the input voltage at A-to-B. Unlike the polarity of VDD to GND, which must be positive, voltage across A-B, W-A, and W-B can be at either polarity.
Figure 32. AD5170 Equivalent RDAC Circuit
The general equation that determines the digitally programmed output resistance between Terminal W and Terminal B is
RWB(D ) = D x RAB + 2 x RW 128
(1)
where D is the decimal equivalent of the binary code loaded in the 8-bit RDAC register, RAB is the end-to-end resistance, and RW is the wiper resistance contributed by the on resistance of the internal switch. In summary, if RAB = 10 k and the A terminal is opencircuited, the output resistance RWB is set for the RDAC latch codes, as shown in Table 5. Table 5. Codes and Corresponding RWB Resistance
D (Dec.) 255 128 1 0 RWB () 9,961 5,060 139 100 Output State Full Scale (RAB - 1 LSB + RW) Midscale 1 LSB Zero Scale (Wiper Contact Resistance)
VI A W VO
04104-0-035
B
Figure 33. Potentiometer Mode Configuration
Note that in the zero-scale condition, a finite wiper resistance of 100 is present. Care should be taken to limit the current flow between Terminal W and Terminal B in this state to a maximum pulse current of no more than 20 mA. Otherwise, degradation or possible destruction of the internal switch contact can occur. Similar to the mechanical potentiometer, the resistance of the RDAC between the wiper, Terminal W, and Terminal A also produces a digitally controlled complementary resistance, RWA. When these terminals are used, the B terminal can be opened. Setting the resistance value for RWA starts at a maximum value of resistance and decreases as the data loaded in the latch increases in value. The general equation for this operation is
RWA(D ) = 256 - D x RAB + 2 x RW 128
If ignoring the effect of the wiper resistance for approximation, connecting the A terminal to 5 V and the B terminal to ground produces an output voltage at the wiper-to-B starting at 0 V up to 1 LSB less than 5 V. Each LSB of voltage is equal to the voltage applied across Terminal AB divided by the 256 positions of the potentiometer divider. The general equation defining the output voltage at VW with respect to ground for any valid input voltage applied to Terminal A and Terminal B is
VW ( D) =
D 256 - D VA + VB 256 256
(3)
For a more accurate calculation, which includes the effect of wiper resistance, VW can be found as
VW (D) =
R (D ) RWB (D) V A + WA VB R AB R AB
(4)
(2)
Operation of the digital potentiometer in the divider mode results in a more accurate operation over temperature. Unlike the rheostat mode, the output voltage is dependent mainly on the ratio of the internal resistors, RWA and RWB, and not the absolute values. Thus, the temperature drift reduces to 15 ppm/C.
Rev. A | Page 13 of 24
AD5170
ESD PROTECTION
All digital inputs--SDA, SCL, AD0, and AD1--are protected with a series input resistor and parallel Zener ESD structures, as shown in Figure 34 and Figure 35.
340 LOGIC
04104-0-037
GND
Figure 34. ESD Protection of Digital Pins
A, B, W
04104-0-038
fuse programming supply (either an on-board regulator or rack-mount power supply) must be rated at 5.25 V to 5.5 V and able to provide a 100 mA current for 400 ms for successful onetime programming. Once fuse programming is completed, the VDD_OTP supply must be removed to allow normal operation at 2.7 V to 5.5 V and the device will consume current in A range. Figure 37 shows the simplest implementation of a dual supply requirement by using a jumper. This approach saves one voltage supply, but draws additional current and requires manual configuration.
5.5V R1 50k CONNECT J1 HERE FOR OTP VDD C1 10F R2 250k CONNECT J1 HERE AFTER OTP
04104-0-049
GND
C2 1nF
AD5170
Figure 35. ESD Protection of Resistor Terminals
TERMINAL VOLTAGE OPERATING RANGE
The AD5170 VDD to GND power supply defines the boundary conditions for proper 3-terminal digital potentiometer operation. Supply signals present on Terminal A, Terminal B, and Terminal W that exceed VDD or GND will be clamped by the internal forward-biased diodes (see Figure 36).
VDD
Figure 37. Power Supply Requirement
An alternate approach in 3.5 V to 5.25 V systems adds a signal diode between the system supply and the OTP supply for isolation, as shown in Figure 38.
5.5V APPLY FOR OTP ONLY D1 3.5V-5.25V C1 1F C2 1nF VDD
A W B
04104-0-039
AD5170
GND
Figure 36. Maximum Terminal Voltages Set by VDD and GND
POWER-UP SEQUENCE
Because the ESD protection diodes limit the voltage compliance at Terminal A, Terminal B, and Terminal W (see Figure 36), it is important to power VDD/GND before applying any voltage to Terminal A, Terminal B, and Terminal W. Otherwise, the diode will be forward biased such that VDD is powered unintentionally and may affect the rest of the user's circuit. The ideal power-up sequence is GND, VDD, the digital inputs, and then VA/VB/VW. The relative order of powering VA, VB, VW, and the digital inputs is not important as long as they are powered after VDD/GND.
Figure 38. Isolate 5.5 V OTP Supply from 3.5 V to 5.25 V Normal Operating Supply. The VDD_OTP must be removed once OTP is completed.
5.5V R1 10k 2.7V P1
APPLY FOR OTP ONLY
VDD P2 C1 10F C2 1nF
AD5170
P1=P2=FDV302P, NDS0610
04104-0-051
POWER SUPPLY CONSIDERATIONS
To minimize the package pin count, both the one-time programming and normal operating voltage supplies share the same VDD terminal of the AD5170. The AD5170 employs fuse link technology that requires 5.25 V to 5.5 V for blowing the internal fuses to achieve a given setting, but normal VDD can be anywhere between 2.7 V and 5.5 V after the fuse programming process. As a result, dual voltage supplies and isolation are needed if system VDD is lower than the required VDD_OTP. The
Figure 39. Isolate 5.5 V OTP Supply from 2.7 V Normal Operating Supply. The VDD_OTP supply must be removed once OTP is completed.
For users who operate their systems at 2.7 V, use of the bidirectional low threshold P-Ch MOSFETs is recommended for the supply's isolation. As shown in Figure 39, this assumes
Rev. A | Page 14 of 24
04104-0-050
AD5170
the 2.7 V system voltage is applied first, and the P1 and P2 gates are pulled to ground, thus turning on P1 and subsequently P2. As a result, VDD of the AD5170 approaches 2.7 V. When the AD5170 setting is found, the factory tester applies the VDD_OTP to both the VDD and the MOSFETs gates turning off P1 and P2. The OTP command is executed at this time to program the AD5170 while the 2.7 V source is protected. Once the fuse programming is completed, the tester withdraws the VDD_OTP and the setting for AD5170 is permanently fixed. AD5170 achieves the OTP function through blowing internal fuses. Users should always apply the 5.25 V to 5.5 V one-time program voltage requirement at the first fuse programming attempt. Failure to comply with this requirement may lead to a change in the fuse structures, rendering programming inoperable. Poor PCB layout introduces parasitics that may affect the fuse programming. Therefore, it is recommended to add a 10 F tantalum capacitor in parallel with a 1 nF ceramic capacitor as close as possible to the VDD pin. The type and value chosen for both capacitors are important. This combination of capacitor values provides both a fast response and larger supply current handling with minimum supply droop during transients. As a result, these capacitors increase the OTP programming success by not inhibiting the proper energy needed to blow the internal fuses. Additionally, C1 minimizes transient disturbance and low frequency ripple while C2 reduces high frequency noise during normal operation.
LAYOUT CONSIDERATIONS
It is good practice to employ compact, minimum lead length layout design. The leads to the inputs should be as direct as possible with a minimum conductor length. Ground paths should have low resistance and low inductance. Note that the digital ground should also be joined remotely to the analog ground at one point to minimize the ground bounce.
VDD C1 10F
+
VDD C2 1nF
AD5170
GND
04104-0-040
Figure 40. Power Supply Bypassing
Rev. A | Page 15 of 24
AD5170 EVALUATION SOFTWARE/HARDWARE
Figure 41. AD5170 Computer Software Interface
There are two ways of controlling the AD5170. Users can either program the devices with computer software or external I2C controllers.
SOFTWARE PROGRAMMING
Due to the advantages of the one-time programmable feature, users may consider programming the device in the factory before shipping the final product to end-users. ADI offers device programming software that can be implemented in the factory on PCs running Windows(R) 95 or later. As a result, external controllers are not required, which significantly reduces development time. The program is an executable file that does not require knowledge of any programming languages or programming skills. It is easy to set up and to use. Figure 41 shows the software interface. The software can be downloaded from www.analog.com.
The AD5170 starts at midscale after power-up prior to OTP programming. To increment or decrement the resistance, the user may simply move the scrollbars on the left. To write any specific value, the user should use the bit pattern in the upper screen and press the Run button. The format of writing data to the device is shown in Table 7. Once the desired setting is found, the user presses the Program Permanent button to blow the internal fuse links. To read the validation bits and data from the device, the user simply presses the Read button. The format of the read bits is shown in Table 8. To apply the device programming software in the factory, users must modify a parallel port cable and configure Pin 2, Pin 3, Pin 15, and Pin 25 for SDA_write, SCL, SDA_read, and DGND, respectively, for the control signals (Figure 42). Users should also lay out the PCB of the AD5170 with SCL and SDA pads, as shown in Figure 43, such that pogo pins can be inserted for factory programming.
Rev. A | Page 16 of 24
AD5170
13 25 12 24 11 23 10 22 9 21 8 20 7 19 6 18 5 17 4 16 3 15 2 14 1
AD5170
B A AD0 GND VDD W NC AD1 SDA SCL
04104-0-043
Figure 43. Recommended AD5170 PCB Layout. The SCL and SDA pads allow pogo pins to be inserted so that signals can be communicated through the parallel port for programming (Figure 42).
R3 100 R2 READ 100 R1 WRITE
04104-0-042
SCL SDA
100
Figure 42. Parallel Port Connection. Pin 2 = SDA_write, Pin 3 = SCL, Pin 15 = SDA_read, and Pin 25 = DGND.
Rev. A | Page 17 of 24
AD5170 I2C INTERFACE
Table 7. Write Mode
S 0 1 0 1 1 AD1 AD0 W Slave Address Byte A 2T SD T 0 OW X Instruction Byte X X A D7 D6 D5 D4 D3 D2 D1 D0 Data Byte A P
Table 8. Read Mode
S 0 1 0 1 1 AD1 AD0 R Slave Address Byte A D7 D6 D5 D4 D3 D2 D1 D0 Instruction Byte A E1 E0 X XXX Data Byte X X A P
S = Start Condition. P = Stop Condition. A = Acknowledge. AD0, AD1 = Package Pin Programmable Address Bits. X = Don't Care. W = Write. R = Read. 2T = Second fuse link array for two-time programming. Logic 0 corresponds to first trim. Logic 1 corresponds to second trim. Note that blowing trim #2 before trim #1 effectively disables trim #1 and in turn only allows one-time programming. SD = Shutdown connects wiper to B terminal and open circuits the A terminal. It does not change the contents of the wiper register.
T = OTP Programming Bit. Logic 1 permanently programs the wiper. OW = Overwrite the fuse setting and program the digital potentiometer to a different setting. Note that upon power-up, the digital potentiometer presets to either midscale or fuse setting depending on whether the fuse link has been blown. D7, D6, D5, D4, D3, D2, D1, D0 = Data Bits. E1, E0 = OTP Validation Bits. 0, 0 = Ready to Program. 1, 0 = Fatal Error. Some fuses not blown. Do not retry. Discard this unit. 1, 1 = Programmed Successfully. No further adjustments are possible.
Rev. A | Page 18 of 24
AD5170
t2
t8
SCL
t6
t9
t2
t3 t8 t9
t4
t7
t5
t10
SDA
t1
P S S P
Figure 44. I2C Interface Detailed Timing Diagram
1 SCL SDA
9
1
9
1
9
ACK BY AD5170 START BY MASTER FRAME 1 SLAVE ADDRESS BYTE FRAME 2 INSTRUCTION BYTE
ACK BY AD5170 FRAME 3 DATA BYTE
ACK BY AD5170
STOP BY MASTER
Figure 45. Writing to the RDAC Register
1 SCL SDA
9
1
9
1
9
ACK BY AD5170 START BY MASTER FRAME 1 SLAVE ADDRESS BYTE FRAME 2 INSTRUCTION BYTE
ACK BY MASTER FRAME 3 DATA BYTE
NO ACK BY MASTER
STOP BY MASTER
Figure 46. Reading Data from the RDAC Register
Rev. A | Page 19 of 24
04104-0-046
0
1
0
1
1
AD1 AD0 R/W
D7
D6
D5
D4
D3
D2
D1
D0
E1
E0
X
X
X
X
X
X
04104-0-045
0
1
0
1
1
AD1 AD0 R/W
A0
SD
T
0
OW
X
X
X
D7
D6
D5
D4
D3
D2
D1
D0
04104-0-044
AD5170
I2C COMPATIBLE 2-WIRE SERIAL BUS
The 2-wire I2C serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a START condition, which is when a high-to-low transition on the SDA line occurs while SCL is high (see Figure 45). The following byte is the slave address byte, which consists of the slave address followed by an R/W bit (this bit determines whether data is read from, or written to, the slave device). AD0 and AD1 are configurable address bits which allow up to four devices on one bus (see Table 7). The slave address corresponding to the transmitted address bits responds by pulling the SDA line low during the ninth clock pulse (this is termed the Acknowledge bit). At this stage, all other devices on the bus remain idle while the selected device waits for data to be written to, or read from, its serial register. If the R/W bit is high, the master will read from the slave device. If the R/W bit is low, the master will write to the slave device. 2. In the write mode, the second byte is the instruction byte. The first bit (MSB), 2T, of the instruction byte is the second trim enable bit. A logic low selects the first array of fuses, and a logic high selects the second array. This means that after blowing the fuses with trim#1, the user still has another chance to blow them again with trim#2. Note that using trim#2 before trim#1 effectively disables trim#1 and, in turn, only allows one-time programming. The second MSB, SD, is a shutdown bit. A logic high causes an open circuit at Terminal A while shorting the wiper to Terminal B. This operation yields almost 0 in rheostat mode or 0 V in potentiometer mode. It is important to note that the shutdown operation does not disturb the contents of the register. When brought out of shutdown, the previous setting is applied to the RDAC. Also, during shutdown, new settings can be programmed. When the part is returned from shutdown, the corresponding VR setting is applied to the RDAC. The third MSB, T, is the OTP (one-time programmable) programming bit. A logic high blows the poly fuses and programs the resistor setting permanently. For example, if the user wanted to blow the first array of fuses, the instruction byte would be 00100XXX. To blow the second array of fuses, the instruction byte would be 10100XXX. A logic low of the T bit simply allows the device to act as a typical volatile digital potentiometer. The fourth MSB must always be at Logic 0. 3. The fifth MSB, OW, is an overwrite bit. When raised to a logic high, OW allows the RDAC setting to be changed even after the internal fuses have been blown. However, once OW is returned to a logic zero, the position of the RDAC returns to the setting prior to overwrite. Because OW is not static, if the device is powered off and on, the RDAC presets to midscale or to the setting at which the fuses were blown, depending on whether the fuses have been permanently set. The remainder of the bits in the instruction byte are Don't Care bits (see Figure 45). After acknowledging the instruction byte, the last byte in write mode is the data byte. Data is transmitted over the serial bus in sequences of nine clock pulses (eight data bits followed by an Acknowledge bit). The transitions on the SDA line must occur during the low period of SCL and remain stable during the high period of SCL (see Figure 44). In the read mode, the data byte follows immediately after the acknowledgment of the slave address byte. Data is transmitted over the serial bus in sequences of nine clock pulses (a slight difference from the write mode, with eight data bits followed by an Acknowledge bit). Similarly, the transitions on the SDA line must occur during the low period of SCL and remain stable during the high period of SCL (see Figure 46). Following the data byte, the validation byte contains two validation bits, E0 and E1. These bits signify the status of the one-time programming (see Figure 46). 4. After all data bits have been read or written, a STOP condition is established by the master. A STOP condition is defined as a low-to-high transition on the SDA line while SCL is high. In write mode, the master pulls the SDA line high during the 10th clock pulse to establish a STOP condition (see Figure 45). In read mode, the master issues a No Acknowledge for the 9th clock pulse (i.e., the SDA line remains high). The master then brings the SDA line low before the 10th clock pulse, which goes high to establish a STOP condition (see Figure 46).
A repeated write function gives the user flexibility to update the RDAC output a number of times after addressing and instructing the part only once. For example, after the RDAC has acknowledged its slave address and instruction bytes in the write mode, the RDAC output updates on each successive byte. If different instructions are needed, the write/read mode has to start again with a new slave address, instruction, and data byte. Similarly, a repeated read function of the RDAC is also allowed.
Rev. A | Page 20 of 24
AD5170
Table 9. Validation Status
E1 0 1 1 E0 0 0 1 Status Ready for Programming. Fatal Error. Some fuses not blown. Do not retry. Discard this unit. Successful. No further programming is possible.
RP RP SDA MASTER SCL 5V SDA SCL SDA AD1 AD0 SCL 5V SDA AD1 AD0 SCL 5V SDA AD1
04104-0-047
5V
SCL
Multiple Devices on One Bus
Figure 47 shows four AD5170s on the same serial bus. Each has a different slave address because the states of their AD0 and AD1 pins are different. This allows each device on the bus to be written to, or read from, independently. The master device output bus line drivers are open-drain pull-downs in a fully I2C compatible interface.
AD1 AD0
AD0
AD5170
AD5170
AD5170
AD5170
Figure 47. Multiple AD5170s on One I2C Bus
Rev. A | Page 21 of 24
AD5170 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
B1 A2 AD0 3 GND 4 VDD 5
10 9
W NC AD1
04104-0-048
AD5170
TOP VIEW
8 7 6
SDA SCL
Figure 48. Pin Configuration
Table 10. Pin Function Descriptions
Pin 1 2 3 4 5 6 7 8 9 10 Mnemonic B A AD0 GND VDD SCL SDA AD1 NC W Description B Terminal. A Terminal. Programmable Address Bit 0 for Multiple Package Decoding. Digital Ground. Positive Power Supply. Serial Clock Input. Positive Edge Triggered. Serial Data Input/Output. Programmable Address Bit 1 for Multiple Package Decoding. No Connect. W Terminal.
Rev. A | Page 22 of 24
AD5170 OUTLINE DIMENSIONS
3.00 BSC
10 6
3.00 BSC
1 5
4.90 BSC
PIN 1 0.50 BSC 0.95 0.85 0.75 0.15 0.00 0.27 0.17 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187BA 1.10 MAX 8 0 0.80 0.60 0.40
SEATING PLANE
0.23 0.08
Figure 49. 10-Lead Mini Small Outline Package [MSOP] (RM-10) Dimensions shown in millimeters
ORDERING GUIDE
Model AD5170BRM2.5 AD5170BRM2.5-RL7 AD5170BRM10 AD5170BRM10-RL7 AD5170BRM50 AD5170BRM50-RL7 AD5170BRM100 AD5170BRM100-RL7 AD5170EVAL1
1
RAB (k) 2.5 2.5 10 10 50 50 100 100
Temperature -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C
Package Description MSOP-10 MSOP-10 MSOP-10 MSOP-10 MSOP-10 MSOP-10 MSOP-10 MSOP-10 Evaluation Board
Package Option RM-10 RM-10 RM-10 RM-10 RM-10 RM-10 RM-10 RM-10
Branding D0Y D0Y D0Z D0Z D0W D0W D0X D0X
The evaluation board is shipped with the 10 k RAB resistor option; however, the board is compatible with all available resistor value options.
Rev. A | Page 23 of 24
AD5170 NOTES
Purchase of licensed I2C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the purchaser under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips.
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04104-0-11/04(A)
Rev. A | Page 24 of 24

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