256-Position I2C®-Compatible
Digital Potentiometer
AD5245
APPLICATIONS
Mechanical potentiometer replacement in new designs
LCD panel VCOM adjustment
LCD panel brightness and contrast control
Transducer adjustment of pressure, temperature, position,
chemical, and optical sensors
RF amplifier biasing
Automotive electronics adjustment
Gain control and offset adjustment
FUNCTIONAL BLOCK DIAGRAM
VDD
A
SCL
I2C INTERFACE
SDA
W
AD0
WIPER
REGISTER
B
POR
03436-001
256-position
End-to-end resistance 5 kΩ, 10 kΩ, 50 kΩ, 100 kΩ
Compact SOT-23-8 (2.9 mm × 3 mm) package
Fast settling time: tS = 5 µs typ on power-up
Full read/write of wiper register
Power-on preset to midscale
Extra package address decode pin AD0
Computer software replaces µC in factory programming
applications
Single supply: 2.7 V to 5.5 V
Low temperature coefficient 45 ppm/°C
Low power: IDD = 8 µA
Wide operating temperature: –40°C to +125°C
Evaluation board available
GND
Figure 1.
PIN CONFIGURATION
W 1
VDD 2
GND 3
SCL 4
8
AD5245
A
B
TOP VIEW
6 AD0
(Not to Scale)
5 SDA
7
03436-002
FEATURES
Figure 2.
GENERAL DESCRIPTION
The AD5245 provides a compact 2.9 mm × 3 mm packaged
solution for 256-position adjustment applications. These
devices perform the same electronic adjustment function as
mechanical potentiometers or variable resistors, with enhanced
resolution, solid-state reliability, and superior low temperature
coefficient performance.
Operating from a 2.7 V to 5.5 V power supply and consuming
less than 8 µA allows usage in portable battery-operated
applications.
Note that the terms digital potentiometer, VR, and RDAC are
used interchangeably.
The wiper settings are controllable through an I2C-compatible
digital interface, which can also be used to read back the wiper
register content. AD0 can be used to place up to two devices on
the same bus. Command bits are available to reset the wiper
position to midscale or to shut down the device into a state of
zero power consumption.
Rev. B
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: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.
AD5245
TABLE OF CONTENTS
Features .............................................................................................. 1
Test Circuits..................................................................................... 12
Applications....................................................................................... 1
Theory of Operation ...................................................................... 13
Functional Block Diagram .............................................................. 1
Programming the Variable Resistor......................................... 13
Pin Configuration............................................................................. 1
Programming the Potentiometer Divider............................... 14
General Description ......................................................................... 1
ESD Protection ........................................................................... 14
Revision History ............................................................................... 2
Terminal Voltage Operating Range ......................................... 14
Electrical Characteristics ................................................................. 3
Power-Up Sequence ................................................................... 14
5 kΩ Version.................................................................................. 3
Layout and Power Supply Bypassing ....................................... 14
10 kΩ, 50 kΩ, 100 kΩ Versions .................................................. 4
Constant Bias to Retain Resistance Setting............................. 15
Timing Characteristics..................................................................... 5
Evaluation Board ........................................................................ 15
5 kΩ, 10 kΩ, 50 kΩ, 100 kΩ Versions........................................ 5
I2C Interface .................................................................................... 16
Absolute Maximum Ratings............................................................ 6
I2C-Compatible 2-Wire Serial Bus ........................................... 16
ESD Caution.................................................................................. 6
Outline Dimensions ....................................................................... 19
Pin Configuration and Function Descriptions............................. 7
Ordering Guide .......................................................................... 19
Typical Performance Characteristics ............................................. 8
REVISION HISTORY
1/06—Rev. A to Rev. B
Changes to Table 3........................................................................... 5
Changes to Ordering Guide ......................................................... 19
3/04—Rev. 0 to Rev. A
Updated Format................................................................ Universal
Changes to Features......................................................................... 1
Changes to Applications ................................................................. 1
Changes to Figure 1......................................................................... 1
Changes to Electrical Characteristics—5 kΩ Version ................ 3
Changes to Electrical Characteristics—10 kΩ, 50 kΩ,
and 100 kΩ Versions ....................................................................... 4
Changes to Timing Characteristics ............................................... 5
Changes to Absolute Maximum Ratings ...................................... 6
Moved ESD Caution to Page .......................................................... 6
Changes to Pin Configuration and Function Descriptions ....... 7
Changes to Figures 22 and 23 ...................................................... 11
Moved Figure 25 to Figure 26 ...................................................... 11
Moved Figure 26 to Figure 27 ...................................................... 11
Moved Figure 27 to Figure 25 ...................................................... 11
Deleted Figures 31 and 32 ............................................................ 12
Changes to Figure 32, Figure 33 and Figure 34 ......................... 12
Changes to Rheostat Operation Section..................................... 13
Added Figure 35............................................................................. 13
Changes to Equation 1 and Equation 2 ...................................... 13
Changes to Table 6 and Table 7.................................................... 13
Added Figure 37 ............................................................................ 14
Changes to Equation 4 .................................................................. 14
Deleted Readback RDAC Value Section .................................... 14
Deleted Level Shifting for Bidirectional Interface Section ...... 14
Moved ESD Protection Section to Page ..................................... 14
Changes to Figure 38 and Figure 39............................................ 14
Moved Terminal Voltage Operating Range Section to Page.... 14
Changes to Figure 40..................................................................... 14
Moved Power-Up Sequence Section to Page ............................. 14
Moved Layout and Power Supply Bypassing Section to Page . 15
Added Constant Bias to Retain Resistance Setting Section..... 15
Added Figure 42 ............................................................................ 15
Added Evaluation Board Section ................................................ 15
Added Figure 43 ............................................................................ 15
Moved I2C Interface Section to Page........................................... 16
Changes to I2C Compatible 2-Wire Serial Bus Section ........... 16
Moved Table 5 and Table 6 to Page ............................................. 17
(Renumbered as Table 8 and Table 9)
Moved Figure 36, Figure 37, and Figure 38 to Page.................. 17
(Renumbered as Figure 44, Figure 45, and Figure 46)
Moved Multiply Devices on One Bus Section to Page ............. 18
Updated Ordering Guide ............................................................. 19
Updated Outline Dimensions...................................................... 19
Moved I2C Disclaimer to Page ..................................................... 20
5/03—Revision 0: Initial Version
Rev. B | Page 2 of 20
AD5245
ELECTRICAL CHARACTERISTICS
5 kΩ VERSION
VDD = 5 V ± 10% or 3 V ± 10%, VA = VDD, VB = 0 V, –40°C < TA < +125°C, 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 = 25°C
Resistance Temperature Coefficient
(∆RAB/RAB)/∆T × 106 VAB = VDD, wiper = no connect
Wiper Resistance
RW
DC CHARACTERISTICS—POTENTIOMETER DIVIDER MODE (Specifications Apply to All VRs)
Differential Nonlinearity4
DNL
Integral Nonlinearity4
INL
Voltage Divider Temperature Coefficient
(∆VW/VW)/∆T × 106
Code = 0x80
Full-Scale Error
VWFSE
Code = 0xFF
Zero-Scale Error
VWZSE
Code = 0x00
RESISTOR TERMINALS
Voltage Range5
VA, VB, VW
f = 1 MHz, measured to GND,
Capacitance A, B6
CA, CB
code = 0x80
f = 1 MHz, measured to GND,
Capacitance W6
CW
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 Capacitance6
CIL
POWER SUPPLIES
Power Supply Range
VDD RANGE
Supply Current
IDD
VIH = 5 V or VIL = 0 V
Power Dissipation8
PDISS
VIH = 5 V or VIL = 0 V, VDD = 5 V
Power Supply Sensitivity
PSS
VDD = +5 V ± 10%, code = midscale
DYNAMIC CHARACTERISTICS6, 9
Bandwidth –3 dB
BW_5K
RAB = 5 kΩ, 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 = 2.5 kΩ, RS = 0
1
Min
Typ1
Max
Unit
–1.5
–4
–30
±0.1
±0.75
+1.5
+4
+30
LSB
LSB
%
ppm/°C
Ω
45
50
–1.5
–1.5
–6
0
±0.1
±0.6
15
–2.5
2
GND
120
+1.5
+1.5
0
6
LSB
LSB
ppm/°C
LSB
LSB
VDD
V
90
95
0.01
1
pF
1
2.4
0.8
2.1
0.6
±1
5
2.7
3
±0.02
5.5
8
44
±0.05
1.2
0.1
1
6
Typical specifications represent average readings at 25°C 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, and 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 × VDD). CMOS logic level inputs result in minimum power dissipation.
9
All dynamic characteristics use VDD = 5 V.
2
Rev. B | Page 3 of 20
pF
µA
nA
V
V
V
V
µA
pF
V
µA
µW
%/%
MHz
%
µs
nV/√Hz
AD5245
10 kΩ, 50 kΩ, 100 kΩ VERSIONS
VDD = 5 V ± 10% or 3 V ± 10%, VA = VDD, VB = 0 V, –40°C < TA < +125°C, unless otherwise noted.
Table 2.
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 = 25°C
Resistance Temperature Coefficient
(∆RAB/RAB)/∆T × 106 VAB = VDD, wiper = no connect
Wiper Resistance
RW
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 × 106
Code = 0x80
Full-Scale Error
VWFSE
Code = 0xFF
Zero-Scale Error
VWZSE
Code = 0x00
RESISTOR TERMINALS
Voltage Range5
VA, VB, VW
Capacitance A, B6
CA, CB
f = 1 MHz, measured to GND,
code = 0x80
Capacitance W6
CW
f = 1 MHz, measured to GND,
code = 0x80
Shutdown Supply Current
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
6
Input Capacitance
CIL
POWER SUPPLIES
Power Supply Range
VDD RANGE
Supply Current
IDD
VIH = 5 V or VIL = 0 V
Power Dissipation7
PDISS
VIH = 5 V or VIL = 0 V, VDD = 5 V
Power Supply Sensitivity
PSS
VDD = 5 V ± 10%,
code = midscale
6, 8
DYNAMIC CHARACTERISTICS
Bandwidth –3 dB
BW
RAB = 10 kΩ/50 kΩ/100 kΩ,
code = 0x80
Total Harmonic Distortion
THDW
VA = 1 V rms, VB = 0 V, f = 1 kHz,
RAB = 10 kΩ
VW Settling Time (10 kΩ/50 kΩ/100 kΩ)
tS
VA = 5 V, VB = 0 V,
±1 LSB error band
Resistor Noise Voltage Density
eN_WB
RWB = 5 kΩ, RS = 0
1
Min
Typ1
Max
Unit
–1
–2
–30
±0.1
±0.25
+1
+2
+30
LSB
LSB
%
ppm/°C
Ω
45
50
–1
–1
–3
0
±0.1
±0.3
15
–1
1
GND
120
+1
+1
0
3
VDD
90
V
pF
95
pF
0.01
1
1
2.4
0.8
2.1
0.6
±1
5
2.7
3
±0.02
5.5
8
44
±0.05
Rev. B | Page 4 of 20
µA
nA
V
V
V
V
µA
pF
V
µA
µW
%/%
600/100/40
kHz
0.1
%
2
µs
9
nV/√Hz
Typical specifications represent average readings at 25°C 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
PDISS is calculated from (IDD × VDD). CMOS logic level inputs result in minimum power dissipation.
8
All dynamic characteristics use VDD = 5 V.
2
LSB
LSB
ppm/°C
LSB
LSB
AD5245
TIMING CHARACTERISTICS
5 KΩ, 10 KΩ, 50 KΩ, 100 KΩ VERSIONS
VDD = 5 V ± 10% or 3 V ± 10%, VA = VDD, VB = 0 V, –40°C < TA < +125°C, unless otherwise noted.
Table 3.
Parameter
Symbol
Conditions
I2C INTERFACE TIMING CHARACTERISTICS2, 3, 4 (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 Time
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
Typical specifications represent average readings at 25°C and VDD = 5 V.
Guaranteed by design and not subject to production test.
See timing diagram (Figure 44) for locations of measured values.
4
Standard I2C mode operation guaranteed by design.
2
3
Rev. B | Page 5 of 20
Min
Typ1
Max
Unit
400
kHz
µs
µs
1.3
0.6
1.3
0.6
0.6
0.9
100
300
300
0.6
µs
µs
µs
µs
ns
ns
ns
µs
AD5245
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 4.
Parameter
VDD to GND
VA, VB, VW to GND
Terminal Current, A to B, A to W, B to W1
Pulsed
Continuous
Digital Inputs and Output Voltage to GND
Operating Temperature Range
Maximum Junction Temperature (TJMAX)
Storage Temperature Range
Lead Temperature (Soldering, 10 sec)
Thermal Resistance2 θJA: SOT-23-8
Value
–0.3 V to +7 V
VDD
±20 mA
±5 mA
0 V to 7 V
–40°C to +125°C
150°C
–65°C to +150°C
245°C
230°C/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)/θJA.
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. B | Page 6 of 20
AD5245
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
GND 3
SCL 4
8
AD5245
A
B
TOP VIEW
6 AD0
(Not to Scale)
5 SDA
7
03436-002
W 1
VDD 2
Figure 3. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
Mnemonic
W
VDD
GND
SCL
SDA
AD0
B
A
Description
W Terminal. GND ≤ VW ≤ VDD.
Positive Power Supply.
Digital Ground.
Serial Clock Input. Positive edge triggered. Pull-up resistor required.
Serial Data Input/Output. Pull-up resistor required.
Programmable Address Bit 0 for Two-Device Decoding.
B Terminal. GND ≤ VB ≤ VDD.
A Terminal. GND ≤ VA ≤ VDD.
Rev. B | Page 7 of 20
AD5245
TYPICAL PERFORMANCE CHARACTERISTICS
1.0
5V
0.8
–40°C
+25°C
+85°C
+125°C
0.8
POTENTIOMETER MODE DNL (LSB)
0.4
0.2
0
–0.2
–0.4
–0.6
–1.0
0
32
64
96
128
160
192
224
256
CODE (Decimal)
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
03436-003
–0.8
0.6
0
96
128
160
192
224
256
Figure 7. DNL vs. Code vs. Temperature, VDD = 5 V
1.0
1.0
5V
3V
5V
3V
0.8
POTENTIOMETER MODE INL (LSB)
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
0
32
64
96
128
160
192
224
256
CODE (Decimal)
–1.0
03436-004
–1.0
0
128
160
192
224
1.0
256
5V
0.8
POTENTIOMETER MODE DNL (LSB)
0.6
96
Figure 8. INL vs. Code vs. Supply Voltages
–40°C
+25°C
+85°C
+125°C
0.8
64
CODE (Decimal)
Figure 5. R-DNL vs. Code vs. Supply Voltages
1.0
32
03436-007
RHEOSTAT MODE DNL (LSB)
64
CODE (Decimal)
Figure 4. R-INL vs. Code vs. Supply Voltages
0.4
0.2
0
–0.2
–0.4
–0.6
3V
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–0.8
–1.0
0
32
64
96
128
160
192
224
CODE (Decimal)
256
03436-005
POTENTIOMETER MODE INL (LSB)
32
Figure 6. INL vs. Code vs. Temperature, VDD = 5 V
–1.0
0
32
64
96
128
160
192
CODE (Decimal)
Figure 9. DNL vs. Code vs. Supply Voltages
Rev. B | Page 8 of 20
224
256
03436-008
RHEOSTAT MODE INL (LSB)
3V
0.6
03436-006
1.0
AD5245
1.0
0.6
2.0
ZSE, ZERO-SCALE ERROR (µA)
0.8
RHEOSTAT MODE INL (LSB)
2.5
–40 °C
+25°C
+85°C
+125°C
0.4
0.2
0
–0.2
–0.4
–0.6
1.5
VDD = 5.5V
1.0
VDD = 2.7V
0.5
0
32
64
96
128
160
192
224
0
–40
03436-009
–1.0
256
CODE (Decimal)
120
10
IDD SUPPLY CURRENT (µA)
RHEOSTAT MODE DNL (LSB)
0.6
80
Figure 13. Zero-Scale Error vs. Temperature
–40°C
+25°C
+85°C
+125°C
0.8
40
TEMPERATURE (°C)
Figure 10. R-INL vs. Code vs. Temperature, VDD = 5 V
1.0
0
03436-012
–0.8
0.4
0.2
0
–0.2
–0.4
–0.6
VDD = 5.5V
1
VDD = 2.7V
0
32
64
96
128
160
192
224
03436-010
–1.0
256
CODE (Decimal)
0.1
–40
40
80
120
TEMPERATURE (°C)
Figure 11. R-DNL vs. Code vs. Temperature, VDD = 5 V
Figure 14. Supply Current vs. Temperature
2.5
70
60
IA SHUTDOWN CURRENT (nA)
2.0
VDD = 2.7V
1.5
VDD = 5.5V
1.0
0.5
50
40
30
VDD = 5V
20
0
40
80
TEMPERATURE (°C)
120
Figure 12. Full-Scale Error vs. Temperature
0
–40
0
40
80
TEMPERATURE (°C)
Figure 15. Shutdown Current vs. Temperature
Rev. B | Page 9 of 20
120
03436-014
10
0
–40
03436-011
FSE, FULL-SCALE ERROR (LSB)
0
03436-013
–0.8
AD5245
REF LEVEL
0.000dB
0
0x40
–12
0x20
–18
100
0x10
–24
0x08
–30
50
MARKER 510 634.725Hz
MAG (A/R)
–9.049dB
0x80
–6
150
0x04
–36
0x02
0x01
–42
0
–48
32
64
96
128
160
192
224
03436-015
0
256
CODE (Decimal)
–60
1k
START 1 000.000Hz
Figure 16. Rheostat Mode Tempco ∆RWB/∆T vs. Code
10k
100k
1M
STOP 1 000 000.000Hz
03436-018
–54
–50
Figure 19. Gain vs. Frequency vs. Code, RAB = 10 kΩ
REF LEVEL
0.000dB
0
160
/DIV
6.000dB
140
0x80
–6
120
0x40
–12
100
0x20
–18
80
–24
60
–30
40
–36
20
–42
MARKER 100 885.289Hz
MAG (A/R)
–9.014dB
0x10
0x08
0x04
0x02
0x01
–48
0
–54
0
32
64
96
128
160
192
224
03436-016
–20
256
CODE (Decimal)
–60
1k
START 1 000.000Hz
/DIV
6.000dB
REF LEVEL
0.000dB
0
MARKER 1 000 000.000Hz
MAG (A/R)
–8.918dB
–18
–24
–30
0x20
–18
0x10
–24
0x08
–30
0x04
0x40
0x20
0x10
0x08
0x04
–36
0x02
0x01
–36
0x02
–42
–42
0x01
–48
–48
MARKER 54 089.173Hz
MAG (A/R)
–9.052dB
0x80
–12
0x40
–12
/DIV
6.000dB
–6
0x80
–6
100k
1M
STOP 1 000 000.000Hz
Figure 20. Gain vs. Frequency vs. Code, RAB = 50 kΩ
Figure 17. Potentiometer Mode Tempco ∆VWB/∆T vs. Code
REF LEVEL
0.000dB
0
10k
03436-019
POTENTIOMETER MODE TEMPCO (ppm/°C)
/DIV
6.000dB
–54
–54
1k
START 1 000.000Hz
10k
100k
1M
STOP 1 000 000.000Hz
03436-017
–60
–60
1k
START 1 000.000Hz
10k
100k
1M
STOP 1 000 000.000Hz
Figure 21. Gain vs. Frequency vs. Code, RAB = 100 kΩ
Figure 18. Gain vs. Frequency vs. Code, RAB = 5 kΩ
Rev. B | Page 10 of 20
03436-020
RHEOSTAT MODE TEMPCO (ppm/°C)
200
AD5245
REF LEVEL
–5.000dB
/DIV
0.500dB
–5.5
5kΩ – 1.026MHz
10kΩ – 511kHz
50kΩ – 101kHz
100kΩ – 54kHz
–6.0
–6.5
–7.0
–7.5
–8.0
1
–8.5
R = 50kΩ
VW
R = 5kΩ
–9.0
SCL
R = 10kΩ
R = 100kΩ
2
03436-024
–9.5
–10.0
100k
1M
START 1 000.000Hz
10M
STOP 1 000 000.000Hz
Figure 22. –3 dB Bandwidth @ Code = 0x80
60
Ch 2 5.00 V BW M 100ns
A CH2 3.00 V
03436-021
Ch 1 200mV BW
–10.5
10k
Figure 25. Large Signal Settling Time, Code 0xFF ≥ 0x00
CODE = 0x80, VA= VDD, VB = 0V
VA = 5V
VB = 0V
PSRR (–dB)
40
PSRR @ VDD = 3V DC ±10% p-p AC
1
VW
20
SCL
2
1k
10k
100k
1M
FREQUENCY (Hz)
Ch 1 100mV BW
03436-022
0
100
Ch 2 5.00 V BW M 200ns A CH1 152mV
Figure 26. Digital Feedthrough
Figure 23. PSRR vs. Frequency
900
03436-025
PSRR @ VDD = 5V DC ±10% p-p AC
VDD = 5V
800
VA = 5V
VB = 0V
700
500
1
CODE = 0x55
400
VW
300
CODE = 0xFF
SCL
200
0
10k
100k
1M
FREQUENCY (Hz)
10M
Ch 1 5.00V BW
Ch 2 5.00 V BW M 200ns
A CH1 3.00 V
Figure 27. Midscale Glitch, Code 0x80 ≥ 0x7F
Figure 24. IDD vs. Frequency
Rev. B | Page 11 of 20
03436-026
2
100
03436-023
IDD (µA)
600
AD5245
TEST CIRCUITS
Figure 28 to Figure 34 illustrate the test circuits that define the test conditions used in the product specification tables (Table 1 through Table 3).
V+ = VDD
1LSB = V+/2N
DUT
W
VOUT
B
OFFSET
GND
–15V
2.5V
Figure 32. Test Circuit for Gain vs. Frequency
NO CONNECT
DUT
B
0.1V
ISW
03436-028
VMS
0.1V
ISW
CODE = 0x00
W
B
GND TO VDD
Figure 29. Test Circuit for Resistor Position Nonlinearity Error
(Rheostat Operation; R-INL, R-DNL)
Figure 33. Test Circuit for Incremental On Resistance
NC
IW = VDD/RNOMINAL
DUT
VW
A
VDD
VMS1
RW = [VMS1 – VMS2]/IW
GND
03436-029
B
W
ICM
B
NC
VCM
NC = NO CONNECT
03436-033
DUT
W
RSW =
DUT
IW
A W
03436-031
VMS
Figure 28. Test Circuit for Potentiometer Divider Nonlinearity Error
(INL, DNL)
VMS2
AD8610
VIN
B
A
+15V
W
03436-032
V+
DUT
A
03436-027
A
Figure 34. Test Circuit for Common-Mode Leakage Current
Figure 30. Test Circuit for Wiper Resistance
VA
V+ = VDD ±10%
A
V+
B
W
PSS (%/%) =
VMS
∆V
(∆VMS
)
DD
∆VMS%
∆VDD %
03436-030
VDD
PSRR (dB) = 20 log
Figure 31. Test Circuit for Power Supply Sensitivity (PSS, PSSR)
Rev. B | Page 12 of 20
AD5245
THEORY OF OPERATION
The general equation determining the digitally programmed
output resistance between W and B is
The AD5245 is a 256-position digitally controlled variable
resistor (VR) device.
An internal power-on preset places the wiper at midscale
during power-on, which simplifies the fault condition recovery
at power-up.
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the RDAC between Terminals A and
B is available in 5 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ. 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 the 256 possible
settings.
03436-034
B
B
B
Figure 35. Rheostat Mode Configuration
Assuming that a 10 kΩ part is used, the wiper’s first connection
starts at the B terminal for Data 0x00. Because there is a 50 Ω
wiper contact resistance, such a connection yields a minimum
of 100 Ω (2 × 50 Ω) resistance between Terminals W and B. The
second connection is the first tap point, which corresponds to
139 Ω (RWB = RAB/256 + 2 × RW = 39 Ω + 2 × 50 Ω) for Data 0x01.
The third connection is the next tap point, representing 178 Ω
(2 × 39 Ω + 2 × 50 Ω) 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 Ω (RAB + 2 × RW).
A
RS
D7
D6
D5
D4
D3
D2
D1
D0
(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.
RW is the wiper resistance contributed by the on resistance of
the internal switch.
In summary, if RAB = 10 kΩ and the A terminal is open
circuited, then the following output resistance RWB is set for the
indicated RDAC latch codes.
D (Dec.)
255
128
1
0
W
W
W
D
× R AB + 2 × RW
256
Table 6. Codes and Corresponding RWB Resistance
A
A
A
RWB (D) =
RWB (Ω)
9,961
5,060
139
100
Output State
Full Scale (RAB – 1 LSB + RW)
Midscale
1 LSB
Zero Scale (Wiper Contact Resistance)
Note that in the zero-scale condition, a finite wiper resistance of
100 Ω is present. Care should be taken to limit the current flow
between W and 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 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) =
RS
256 − D
× R AB + 2 × RW
256
(2)
For RAB = 10 kΩ and the B terminal open circuited, the
following output resistance RWA is set for the indicated RDAC
latch codes.
RS
W
Table 7. Codes and Corresponding RWA Resistance
RDAC
RS
B
03436-035
LATCH
AND
DECODER
Figure 36. AD5245 Equivalent RDAC Circuit
D (Dec.)
255
128
1
0
RWA (Ω)
139
5,060
9,961
10,060
Output State
Full Scale
Midscale
1 LSB
Zero Scale
Typical device-to-device matching is process lot dependent and
can vary by up to ±30%. Because the resistance element is
processed in thin film technology, the change in RAB with
temperature has a very low 45 ppm/°C temperature coefficient.
Rev. B | Page 13 of 20
AD5245
PROGRAMMING THE POTENTIOMETER DIVIDER
TERMINAL VOLTAGE OPERATING RANGE
Voltage Output Operation
The AD5245 VDD and GND power supply defines the boundary
conditions for proper 3-terminal digital potentiometer
operation. Supply signals present on Terminals A, B, and W that
exceed VDD or GND are clamped by the internal forward-biased
diodes (see Figure 40).
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 to B, W to A, and W to B can be at
either polarity.
VDD
A
W
A
B
VO
03436-036
W
B
GND
03436-039
VI
Figure 40. Maximum Terminal Voltages Set by VDD and GND
Figure 37. Potentiometer Mode Configuration
POWER-UP SEQUENCE
If ignoring the effect of the wiper resistance for approximation,
then 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 A and B 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 Terminals A and B is
VW (D) =
D
256 − D
VA +
VB
256
256
(3)
LAYOUT AND POWER SUPPLY BYPASSING
A more accurate calculation, which includes the effect of wiper
resistance, VW, is
VW (D) =
R (D)
RWB (D)
V A + WA
VB
R AB
R AB
(4)
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, not the absolute
values. Therefore, the temperature drift reduces to 15 ppm/°C.
ESD PROTECTION
All digital inputs are protected with a series of input resistors and
parallel Zener ESD structures, shown in Figure 38 and Figure 39.
This applies to the digital input pins SDA, SCL, and AD0.
GND
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.
Similarly, it is also good practice to bypass the power supplies
with quality capacitors for optimum stability. Supply leads to
the device should be bypassed with disk or chip ceramic
capacitors of 0.01 µF to 0.1 µF. Low ESR 1 µF to 10 µF tantalum
or electrolytic capacitors should also be applied at the supplies
to minimize any transient disturbance and low frequency ripple
(see Figure 41). Note that the digital ground should also be
joined remotely to the analog ground at one point to minimize
the ground bounce.
VDD
LOGIC
03436-037
340Ω
Because the ESD protection diodes limit the voltage compliance
at Terminals A, B, and W (see Figure 40), it is important to
power VDD and GND before applying any voltage to Terminals
A, B, and W; otherwise, the diode is forward biased such that
VDD is powered unintentionally and can affect the rest of the
user’s circuit. The ideal power-up sequence is in the following
order: GND, VDD, digital inputs, and then VA, VB, and VW. The
relative order of powering VA, VB, VW, and the digital inputs is
not important as long as they are powered after VDD and GND.
C3
10µF
+
C1
0.1µF
VDD
AD5245
Figure 38. ESD Protection of Digital Pins
GND
03436-038
GND
03436-040
A, B, W
Figure 41. Power Supply Bypassing
Figure 39. ESD Protection of Resistor Terminals
Rev. B | Page 14 of 20
AD5245
CONSTANT BIAS TO RETAIN RESISTANCE SETTING
For users who desire nonvolatility but cannot justify the
additional cost for the EEMEM, the AD5245 can be considered
a low cost alternative by maintaining a constant bias to retain
the wiper setting. The AD5245 is designed specifically with low
power in mind, which allows low power consumption even in
battery-operated systems. Figure 42 demonstrates the power
consumption from a 3.4 V, 450 mA-hr Li-Ion cell phone battery
that is connected to the AD5245. The measurement over time
shows that the device draws approximately 1.3 µA and
consumes negligible power. Over a course of 30 days, the
battery is depleted by less than 2%, the majority of which is due
to the intrinsic leakage current of the battery itself.
110%
Although the resistance setting of the AD5245 is lost when the
battery needs replacement, such events occur rather infrequently
so that this inconvenience is justified by the lower cost and
smaller size offered by the AD5245. If total power is lost, then
the user should be provided with a means to adjust the setting
accordingly.
EVALUATION BOARD
An evaluation board, along with all necessary software, is
available to program the AD5245 from any PC running
Windows® 98/2000/XP. The graphical user interface, as shown
in Figure 43, is straightforward and easy to use. More detailed
information is available in the user manual, which is provided
with the board.
TA = 25°C
108%
104%
102%
100%
98%
96%
03436-042
BATTERY LIFE DEPLETED
106%
94%
92%
Figure 43. AD5245 Evaluation Board Software
0
5
10
15
DAYS
20
25
30
03436-041
90%
Figure 42. Battery Operating Life Depletion
This demonstrates that constantly biasing the potentiometer
can be a practical approach. Most portable devices do not
require the removal of batteries for charging.
The AD5245 starts at midscale upon power-up. To increment or
decrement the resistance, the user can simply move the scrollbars on the left. To write a specific value, the user should use the
bit pattern in the upper screen and click the Run button. The
format of writing data to the device is shown in Table 8. To read
the data from the device, the user can simply click the Read
button. The format of the read bits is shown in Table 9.
Rev. B | Page 15 of 20
AD5245
I2C INTERFACE
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 next byte
is the slave address byte, which consists of the 7-bit slave
address followed by an R/W bit (this bit determines whether
data is read from or written to the slave device). The AD5245
has one configurable address bit, AD0 (see Table 8).
The slave whose address corresponds to the transmitted
address 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 reads
from the slave device. On the other hand, if the R/W bit is
low, the master writes to the slave device.
2. In write mode, the second byte is the instruction byte.
The first bit (MSB) of the instruction byte is a don’t care.
The second MSB, RS, is the midscale reset. A logic high on
this bit moves the wiper to the center tap, where RWA = RWB.
This feature effectively overwrites the contents of the
register; therefore, when taken out of reset mode, the RDAC
remains at midscale.
The third 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 Ω 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.
3. 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 45).
4. In 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 with write mode, in which eight
data bits are 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).
5. 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 ninth clock pulse (that is, 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, then 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.
The remainder of the bits in the instruction byte are don’t
cares (see Table 8).
Rev. B | Page 16 of 20
AD5245
Table 8. Write Mode
S 0 1 0 1 1 0 AD0
A
W
X RS
SD
Slave Address Byte
X X X X X A D7
D6
D5
D4
Instruction Byte
D3
D2
D1
D0
A P
Data Byte
Table 9. Read Mode
0
1
0
1
1
0
AD0
Slave Address Byte
R
A
D7
D6
D5
S = START condition
P = STOP condition
A = Acknowledge
X = Don’t care
W = Write
D4
D3
Data Byte
D2
D1
D0
A
P
R = Read
RS = Reset wiper to midscale 0x80
SD = Shutdown connects wiper to B terminal and open circuits
A terminal, but does not change contents of wiper register
D7, D6, D5, D4, D3, D2, D1, D0 = Data Bits
t8
t2
t9
SCL
t6
t2
t3
t7
t4
t10
t5
t9
t8
SDA
P
S
S
03436-043
t1
P
Figure 44. I2C Interface Detailed Timing Diagram
1
9
9
1
1
9
SCL
0
1
1
0
1
0
X
AD0 R/W
RS
SD
X
X
X
X
X
ACK BY
AD5245
START BY
MASTER
D7
D6
D5
D4
D3
D2
D1
D0
ACK BY
AD5245
FRAME 1
SLAVE ADDRESS BYTE
FRAME 2
INSTRUCTION BYTE
FRAME 3
DATA BYTE
ACK BY
AD5245
STOP BY
MASTER
Figure 45. Writing to the RDAC Register
1
9
1
9
SCL
SDA
START BY
MASTER
0
1
0
1
1
0
FRAME 1
SLAVE ADDRESS BYTE
AD0
D7
R/W
D6
ACK BY
AD5245
D5
D4
D3
D2
D1
FRAME 2
RDAC REGISTER
Figure 46. Reading Data from a Previously Selected RDAC Register in Write Mode
Rev. B | Page 17 of 20
D0
NO ACK
BY MASTER
STOP BY
MASTER
03436-044
SDA
03436-045
S
AD5245
+5V
Multiple Devices on One Bus
RP
RP
SDA
MASTER
SCL
+5V
SDA SCL
SDA SCL
AD0
AD0
AD5245
AD5245
Figure 47. Multiple AD5245 Devices on One I2C Bus
Rev. B | Page 18 of 20
03436-046
Figure 47 shows two AD5245 devices on the same serial bus.
Each has a different slave address because the states of their
AD0 pins are different. This allows the RDAC within each
device to be written to or read from independently. The master
device’s output bus line drivers are open-drain pull-downs in a
fully I2C-compatible interface.
AD5245
OUTLINE DIMENSIONS
2.90 BSC
8
7
6
5
1
2
3
4
1.60 BSC
2.80 BSC
PIN 1
INDICATOR
0.65 BSC
1.95
BSC
1.30
1.15
0.90
1.45 MAX
0.15 MAX
0.38
0.22
0.22
0.08
8°
4°
0°
SEATING
PLANE
0.60
0.45
0.30
COMPLIANT TO JEDEC STANDARDS MO-178-BA
Figure 48. 8-Lead Small Outline Transistor Package [SOT-23]
(RJ-8)
Dimensions shown in millimeters
ORDERING GUIDE
Model
AD5245BRJ5-R2
AD5245BRJ5-RL7
AD5245BRJZ5-R21
AD5245BRJZ5-RL71
AD5245BRJ10-R2
AD5245BRJ10-RL7
AD5245BRJZ10-R21
AD5245BRJZ10-RL71
AD5245BRJ50-R2
AD5245BRJ50-RL7
AD5245BRJZ50-R21
AD5245BRJZ50-RL71
AD5245BRJ100-R2
AD5245BRJ100-RL7
AD5245BRJZ100-R21
AD5245BRJZ100-RL71
AD5245EVAL2
1
2
Temperature Range
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
Package Description
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
8-Lead SOT-23
Evaluation Board
Package Option
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
RJ-8
Branding
D0G
D0G
D0G
D0G
D0H
D0H
D0H
D0H
D0J
D0J
D0J
D0J
D0K
D0K
D0K
D0K
RAB (Ω)
5k
5k
5k
5k
10 k
10 k
10 k
10 k
50 k
50 k
50 k
50 k
100 k
100 k
100 k
100 k
Z = Pb-free part.
The evaluation board is shipped with the 10 kΩ RAB resistor option; however, the board is compatible with all available resistor value options.
Rev. B | Page 19 of 20
Ordering Quantity
250
3,000
250
3,000
250
3,000
250
3,000
250
3,000
250
3,000
250
3,000
250
3,000
AD5245
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.
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C03436-0-1/06(B)
Rev. B | Page 20 of 20
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