CAT5172
Digital Potentiometer (POT),
256-Tap, SPI Compatible
The CAT5172 is a 256-position digital linear taper potentiometer
ideally suited for replacing mechanical potentiometers and variable
resistors. Like mechanical potentiometers, the CAT5172 has a
resistive element, which can span VCC to Ground or float anywhere
between the power supply rails.
Wiper settings are controlled through an SPI-compatible digital
interface. Upon power-up, the wiper assumes a mid-span position and
may be repositioned anytime after the power is stable.
The CAT5172 operates from 2.7 V to 5.5 V, while consuming less
than 2 mA. This low operating current, combined with a small package
footprint, make the CAT5172 ideal for battery-powered portable
appliance.
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SOT23−8
TB SUFFIX
CASE 527AK
Features
256-position
End-to-End Resistance: 50 kW, 100 kW
SPI Compatible Interface
Power-on Preset to Midscale
Single Supply 2.7 V to 5.5 V
Low Temperature Coefficient 100 ppm/C
Low Power, IDD 2 mA max
Wide Operating Temperature −40C to +85C
SOT−23 8-lead (2.9 mm 3 mm) Package
These Devices are Pb-Free, Halogen Free/BFR Free and are RoHS
Compliant
MARKING DIAGRAM
ADYM
1
1
AD = 50 kW
AE = 100 kW
Y = Production Year
Y = (Last Digit)
M = Production Month
M = (1 − 9, A, B, C)
Typical Applications
Potentiometer Replacement
Transducer Adjustment of Pressure, Temperature, Position,
Chemical, and Optical Sensors
RF Amplifier Biasing
Gain Control and Offset Adjustment
AEYM
PIN CONNECTIONS
W
A
1
B
VDD
GND
CS
CLK
SDI
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 2 of this data sheet.
Semiconductor Components Industries, LLC, 2013
July, 2013 − Rev. 1
1
Publication Order Number:
CAT5172/D
CAT5172
VDD
CS
SDI
CLK
SPI
INTERFACE
A
W
B
WIPER
REGISTER
GND
Figure 1. Functional Block Diagram
Table 1. ORDERING INFORMATION
Part Number
Resistance
CAT5172TBI−50GT3
50 kW
CAT5172TBI−00GT3
100 kW
Temperature Range
Package
Shipping†
−40C to 85C
SOT−23−8
(Pb−Free)
3000/Tape & Reel
3000/Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
1. For detailed information and a breakdown of device nomenclature and numbering systems, please see the ON Semiconductor Device
Nomenclature document, TND310/D, available at www.onsemi.com.
Table 2. PIN FUNCTION DESCRIPTION
Pin No.
Pin Name
Description
1
W
2
VDD
Positive Power Supply.
3
GND
Digital Ground.
4
CLK
Serial Clock Input. Positive edge triggered.
5
SDI
Serial Data Input.
6
CS
7
B
Bottom Terminal of resistive element.
8
A
Top Terminal of resistive element.
Resistor’s Wiper Terminal.
Chip Select Input, Active Low. When CS returns high, data will be loaded into the DAC register.
Table 3. ABSOLUTE MAXIMUM RATINGS (Note 2)
Rating
VDD to GND
Value
Unit
−0.3 to 6.5
V
VA, VB, VW to GND
VDD
IMAX
20
mA
0 to 6.5
V
−40 to +85
C
150
C
−65 to +150
C
300
C
Digital Inputs and Output Voltage to GND
Operating Temperature Range
Maximum Junction Temperature (TJMAX)
Storage Temperature
Lead Temperature (Soldering, 10 sec)
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
2. Maximum terminal current is bounded 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.
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CAT5172
Table 4. ELECTRICAL CHARACTERISTICS: 50 kW and 100 kW Versions
VDD = 5 V 10%, or 3 V 10%; VA = VDD; VB = 0 V; –40C < TA < +85C; unless otherwise noted.
Test Conditions
Symbol
Min
Typ
(Note 3)
Max
Unit
Resistor Differential Nonlinearity (Note 4)
RWB, VA = no connection
R−DNL
−1
0.1
+1
LSB
Resistor Integral Nonlinearity (Note 4)
RWB, VA = no connection
R−INL
−2
0.4
+2
LSB
Nominal Resistor Tolerance (Note 5)
TA = 25C
nRAB
−20
+20
%
Resistance Temperature Coefficient
VAB = VDD, Wiper = no connection
nRAB/nT
100
VDD = 5 V
RW
50
120
100
250
Parameter
DC CHARACTERISTICS − RHEOSTAT MODE
Wiper Resistance
VDD = 3 V
ppm/C
W
DC CHARACTERISTICS − POTENTIOMETER DIVIDER MODE
N
Resolution
8
Bits
Differential Nonlinearity (Note 6)
DNL
−1
0.1
+1
LSB
Integral Nonlinearity (Note 6)
INL
−1
0.4
+1
LSB
Voltage Divider Temperature Coefficient
Code = 0x80
nVW/nT
100
ppm/C
Full-Scale Error
Code = 0xFF
VWFSE
−3
−1
0
LSB
Zero-Scale Error
Code = 0x00
VWZSE
0
1
3
LSB
VA,B,W
GND
VDD
V
RESISTOR TERMINALS
Voltage Range (Note 7)
Capacitance (Note 8) A, B
f = 1 MHz, measured to GND,
Code = 0 x 80
CA,B
45
pF
Capacitance (Note 8) W
f = 1 MHz, measured to GND,
Code = 0 x 80
CW
60
pF
VA = VB = VDD/2
ICM
1
nA
Input Logic High
VDD = 5 V
VIH
Input Logic Low
VDD = 5 V
VIL
Input Logic High
VDD = 3 V
VIH
Input Logic Low
VDD = 3 V
VIL
Common-Mode Leakage (Note 8)
DIGITAL INPUTS
Input Current
VIN = 0 V or 5 V
Input Capacitance (Note 8)
0.7 x VDD
V
0.3VDD
0.7 x VDD
V
IIL
CIL
V
0.3VDD
V
1
mA
5
pF
POWER SUPPLIES
VDD RANGE
Power Supply Range
Supply Current
Power Dissipation (Note 9)
Power Supply Sensitivity
2.7
0.3
5.5
V
2
mA
VIH = 5 V or VIL = 0 V
IDD
VIH = 5 V or VIL = 0 V, VDD = 5 V
PDISS
0.2
mW
nVDD = +5 V 10%, Code = Midscale
PSS
0.05
%/%
3. Typical specifications represent average readings at +25C and VDD = 5 V.
4. 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.
5. VAB = VDD, Wiper (VW) = no connect.
6. INL and DNL are measured at VW with the digital POT 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.
7. Resistor terminals A, B, W have no limitations on polarity with respect to each other.
8. Guaranteed by design and not subject to production test.
9. PDISS is calculated from (IDD x VDD). CMOS logic level inputs result in minimum power dissipation.
10. All dynamic characteristics use VDD = 5 V.
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CAT5172
Table 4. ELECTRICAL CHARACTERISTICS: 50 kW and 100 kW Versions (continued)
VDD = 5 V 10%, or 3 V 10%; VA = VDD; VB = 0 V; –40C < TA < +85C; unless otherwise noted.
Parameter
Min
Typ
(Note 3)
Test Conditions
Symbol
Max
Unit
RAB = 50 kW / 100 kW, Code = 0x80
BW
100/40
kHz
VA =1 V rms, VB = 0 V,
f = 1 kHz, RAB = 10 kW
THDW
0.05
%
VA = 5 V, VB = 0 V, 1 LSB error band
tS
2
ms
DYNAMIC CHARACTERISTICS (Notes 8 and 10)
Bandwidth –3 dB
Total Harmonic Distortion
VW Settling Time (50 kW/100 kW)
3. Typical specifications represent average readings at +25C and VDD = 5 V.
4. 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.
5. VAB = VDD, Wiper (VW) = no connect.
6. INL and DNL are measured at VW with the digital POT 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.
7. Resistor terminals A, B, W have no limitations on polarity with respect to each other.
8. Guaranteed by design and not subject to production test.
9. PDISS is calculated from (IDD x VDD). CMOS logic level inputs result in minimum power dissipation.
10. All dynamic characteristics use VDD = 5 V.
Table 5. TIMING CHARACTERISTICS: 50 kW and 100 kW Versions
VDD = 5 V 10%, or 3 V 10%; VA = VDD; VB = 0 V; –40C < TA < +85C; unless otherwise noted.
Parameter
Test Conditions
Symbol
Min
Typ
(Note 11)
Max
Unit
25
MHz
SPI INTERFACE TIMING CHARACTERISTICS (Notes 12 and 13) (Specifications Apply to All Parts)
fCLK
Clock Frequency
Input Clock Pulse width
Clock level high or low
tCH, tCL
20
ns
Data Setup Time
tDS
5
ns
Data Hold Time
tDH
5
ns
CS Setup Time
TCSS
15
ns
CS High Pulse Width
TCSW
40
ns
CLK Fall to CS Fall Hold Time
TCSH0
0
ns
CLK Fall to CS Rise Hold Time
TCSH1
0
ns
CS Rise to Clock Rise Setup
TCS1
10
ns
11. Typical specifications represent average readings at +25C and VDD = 5 V.
12. Guaranteed by design and not subject to production test.
13. See timing diagram for location of measured values. All input control voltages are specified with tR = tF = 2 ns (10% to 90% of 3 V) and timed
from a voltage level of 1.5 V.
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CAT5172
SPI INTERFACE
Table 6. CAT5172 SERIAL DATA−WORD FORMAT
B7
B6
B5
B4
B3
B2
B1
B0
D7
MSB
27
D6
D5
D4
D3
D2
D1
D0
LSB
20
CS
1
2
3
4
5
6
7
8
CLK
DATA IN
D7 D6 D5 D4 D3 D2 D1 D0
SDI
VOUT
V1
V2
Figure 2. CAT5172 SPI Interface Timing Diagram (VA = 5 V, VB = 0 V, VW = VOUT)
1
SDI
(DATA IN) 0
CLK
tCSHO
Dx
tCH
1
0
1
CS
Dx
tCSS
tDS
tDH
tCS1
tCSH1
tCL
tCSW
0
tS
VOUT
VW
1 LSB
VW0
Figure 3. SPI Interface Detailed Timing Diagram (VA = 5 V, VB = 0 V, VW = VOUT)
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CAT5172
TYPICAL CHARACTERISTICS
0.03
0.1
0.02
0
DNL
ERROR (LSB)
ERROR (LSB)
0.01
0
−0.01
−0.02
−0.1
INL
−0.2
−0.3
−0.03
−0.4
−0.04
−0.05
0
32
64
96
128
160
192
224
−0.5
256
0
32
64
96
128
160
192
TAP
TAP
Figure 4. Differential Non−Linearity,
VCC = 5.6 V
Figure 5. Integral Non−Linearity,
VCC = 5.6 V
120
6
100
5
224 256
5.6 V
VCC = 2.6 V
60
3.3 V
40
4.0 V
3
3.3 V
2
20
0
5.0 V
4
Vw (V)
Rw (W)
80
5.6 V
4.0 V
0
50
100
VCC = 2.6 V
1
150
200
0
250
0
52
104
156
TAP
TAP
Figure 6. Wiper Resistance at Room
Temperature
Figure 7. Wiper Voltage
208
260
70
100
102.15
0.4
102.10
102.05
0.2
D (%)
R (kW)
102.00
101.95
101.90
0
101.85
101.80
−0.2
−50
−20
10
40
70
101.75
−50
100
−20
10
40
TEMPERATURE (C)
TEMPERATURE (C)
Figure 8. Change in End−to−End Resistance
Figure 9. End−to−End Resistance vs.
Temperature
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CAT5172
TYPICAL CHARACTERISTICS
400
CS
350
T = 90C
W
ISB (nA)
300
T = −45C
250
T = 25C
200
150
100
2
3
4
5
6
VCC (V)
Figure 10. Wiper’s Transition from Position
0xFF to Position 0x00 Relative to the CS
Disable, VCC = 5 V
Figure 11. Standby Current
0
30
−6
25
VCC = 5 V
PSRR (dB)
A (dB)
−12
VCC = 3 V
−18
−24
−30
−36
20
VCC = 5 V
15
VCC = 3 V
10
5
1
10
100
1000
0
1
10
100
f (KHz)
f (KHz)
Figure 12. Gain vs. Bandwidth (Tap 0x80)
Figure 13. PSRR
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1000
CAT5172
BASIC OPERATION
In the power-up cycle, the input data register is cleared,
setting all bits to 0 and the wiper register is loaded with 0x80
(128 Decimal) which moves the wiper to its midscale
position. If CS is toggled CAT5172 transfers the contents of
the input data register (0x00) to the wiper register moving
the wiper to the bottom-most position (W = terminal B). This
transfer is independent of whether new data has been input
or not because CS acts as the transfer command.
The CAT5172 is a 256-position digitally controlled
potentiometer. When power is first applied the wiper
assumes a mid-scale position and will remain there as long
as CS remians high. Once the power supply is stable the
wiper may be repositioned via the SPI compatible interface.
The rising edge of the CS signal acts as the transfer
command and each time CS transitions from LOW to HIGH
the contents of the input register are loaded into the wiper
register.
PROGRAMMING: VARIABLE RESISTOR
Rheostat Mode
The equation for determining the digitally programmed
output resistance between W and B is
The resistance between terminals A and B, RAB, has a
nominal value of 50 kW or 100 kW and has 256 contact
points accessed by the wiper terminal, plus the B terminal
contact. Data in the 8-bit Wiper register is decoded to select
one of these 256 possible settings.
The wiper’s first connection is at the B terminal,
corresponding to control position 0x00. Ideally this would
present a 0 W between the Wiper and B, but just as with a
mechanical rheostat there is a small amount of contact
resistance to be considered, there is a wiper resistance
comprised of the RON of the FET switch connecting the
wiper output with its respective contact point. In CAT5172
this ‘contact’ resistance is typically 50 W. Thus a connection
setting of 0x00 yields a minimum resistance of 50 W
between terminals W and B.
For a 100 kW device, the second connection, or the first tap
point, corresponds to 441 W (RWB = RAB/256 + RW = 390.6
+ 50 W) for data 0x01. The third connection is the next tap
point, is 831 W (2 390.6 + 50 W) for data 0x02, and so on.
Figure 14 shows a simplified equivalent circuit where the
last resistor string will not be accessed; therefore, there is
1 LSB less of the nominal resistance at full scale in addition
to the wiper resistance.
R WB + D R AB ) R W
256
where D is the decimal equivalent of the binary code loaded
in the 8-bit Wiper 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 = 100 kW and the A terminal is open
circuited, the following output resistance RWB will be set for
the indicated Wiper register codes:
Table 7. CODES AND CORRESPONDING RWB
RESISTANCE FOR RAB = 100 kW, VDD = 5 V
RS
RS
RS
W
RS
D (Dec.)
RWB (W)
Output State
255
99,559
Full Scale (RAB – 1 LSB + RW)
128
50,050
Midscale
1
441
1 LSB
0
50
Zero Scale
(Wiper Contact Resistance)
Be aware that in the zero-scale position, the wiper
resistance of 50 W is still present. Current flow between W
and B in this condition should be limited to a maximum
pulsed current of no more than 20 mA. Failure to heed this
restriction can cause degradation or possible destruction of
the internal switch contact.
Similar to the mechanical potentiometer, the resistance of
the digital POT 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
A
Wiper
Register
and
Decoder
(eq. 1)
R WA(D) + 256 * D R AB ) R W
256
(eq. 2)
For RAB = 100 kW and the B terminal open circuited, the
following output resistance RWA will be set for the indicated
Wiper register codes.
B
Figure 14. CAT5172 Equivalent Digital POT Circuit
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CAT5172
Terminal Voltage Operating Range
Table 8. CODES AND CORRESPONDING RWA
RESISTANCE FOR RAB = 100 kW, VDD = 5 V
D (Dec.)
RWA (W)
255
441
Full Scale
128
50,050
Midscale
1
99,659
1 LSB
0
100,050
Zero Scale
The CAT5172 VDD and GND power supply define the
limits for proper 3-terminal digital potentiometer operation.
Signals or potentials applied to terminals A, B or the wiper
must remain inside the span of VDD and GND. Signals
which attempt to go outside these boundaries will be
clamped by the internal forward biased diodes.
Output State
VDD
Typical device to device resistance matching is lot
dependent and may vary by up to 20%.
W, A, B
SPI Compatible 3-wire Serial Bus
Control of CAT5172 is through a 3-wire SPI compatible
digital interface (SDI, CS, and CLK).
The CLK input is rising-edge sensitive and requires crisp
transitions to avoid clocking incorrect data into the serial
input register. When CS is low, the clock loads data into the
serial register on each positive clock edge (Figure 1). Each
8-bit serial word must be loaded starting with the MSB. The
format of the word is shown in Table 6.
Data loaded into CAT5172’s 8-bit serial input register is
transferred to the internal Wiper register when the CS line
returns to logic high. Extra MSB bits are ignored.
CAT5172
LOGIC
GND
Figure 16.
Power-up Sequence
Because ESD protection diodes limit the voltage
compliance at terminals A, B, and W (see Figure 15), it is
recommended that VDD/GND be powered before applying
any voltage to terminals A, B, and W. The ideal power-up
sequence is: GND, VDD, digital inputs, and then VA/B/W. The
order of powering VA, VB, VW, and the digital inputs is not
important as long as they are powered after VDD/GND.
ESD Protection
Digital
Input
LOGIC
Power Supply Bypassing
Good design practice employs compact, minimum lead
length layout design. Leads should be as direct as possible.
It is also recommended to bypass the power supplies with
quality low ESR Ceramic chip capacitors of 0.01 mF to
0.1 mF. Low ESR 1 mF to 10 mF tantalum or electrolytic
capacitors can also be applied at the supplies to suppress
transient disturbances and low frequency ripple. As a further
precaution digital ground should be joined remotely to the
analog ground at one point to minimize the ground bounce.
GND
Potentiometer
VDD
GND
VDD
C3
10 mF
Figure 15. ESD Protection Networks
+
C1
0.1 mF
CAT5172
GND
Figure 17. Power Supply Bypassing
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MECHANICAL CASE OUTLINE
PACKAGE DIMENSIONS
SOT−23, 8 Lead
CASE 527AK−01
ISSUE A
DATE 18 MAR 2009
SYMBOL
E1
e
E
b
PIN #1 IDENTIFICATION
NOM
MAX
A
0.90
1.45
A1
0.00
0.15
A2
0.90
A3
0.60
0.80
b
0.28
0.38
c
0.08
0.22
1.10
1.30
D
2.90 BSC
E
2.80 BSC
E1
1.60 BSC
e
0.65 BSC
L
TOP VIEW
MIN
0.45
0.30
0.60
L1
0.60 REF
L2
0.25 REF
θ
0°
8°
D
A2
A
A3
A1
SIDE VIEW
q
c
L1
L
L2
END VIEW
Notes:
(1) All dimensions in millimeters. Angles in degrees.
(2) Complies with JEDEC standard MO-178.
DOCUMENT NUMBER:
DESCRIPTION:
98AON34327E
SOT−23, 8 LEAD
Electronic versions are uncontrolled except when accessed directly from the Document Repository.
Printed versions are uncontrolled except when stamped “CONTROLLED COPY” in red.
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