AN1316

AN1316
Using Digital Potentiometers for
Programmable Amplifier Gain
Author:
Mark Palmer
Microchip Technology Inc.
INTRODUCTION
Usually a sensor requires its output signal to be
amplified before being converted to a digital
representation. Many times an operational amplifier (op
amp) is used to implement a signal gain circuit. The
programmability of this type of circuit allows the
following issues to be solved:
• Optimization of the sensor output voltage range
• Calibration of the amplifier circuit’s gain
• Adapting gain to input signal variations
- sensor characteristics change over
temperature/voltage
- multiple input sources into a single gain
circuit
• Field calibration updates
• Increased reliability vs mechanical potentiometer
• BOM consolidation – one op amp and one digital
potentiometer supporting the various sensor
options
This Application Note will discuss implementations of
programmable gain circuits using an op amp and a digital potentiometer. This discussion will include implementation details for the digital potentiometer’s resistor
network. It is important to understand these details to
understand the effects on the application.
OVERVIEW OF AMPLIFIER GAIN
CIRCUIT
Figure 1 shows two examples of amplifier circuits with
programmable gain. Circuit “a” is an inverting amplifier
circuit, while circuit “b” is a non-inverting amplifier
circuit.
In these circuits, R1, R2 and Pot1 are used to tune the
gain of the amplifier. The selection of these
components will determine the range and the accuracy
of the gain programming.
The inverting amplifier’s gain is the negative ratio of
(R2 + RBW)/(R1 + RAW). The non-inverting amplifier’s
gain is the ratio of ((R2 + RBW)/(R1 + RAW) + 1). The
feedback capacitor (CF) may be used if additional
circuit stability is required.
These circuits can be simplified by removing resistors
R1 and R2 (R1 = R2 = 0) and just using the digital
potentiometers RAW and RBW ratio to control the gain.
The simplified circuit reduces the cost and board area
but there are trade-offs (for the same resistance and
resolution). Table 1 shows some of the trade-offs with
respect to the gain range that can be achieved, where
the RAB resistance is the typical RAB value and the R1
and R2 resistance values are varied. A more detailed
discussion is included later in this Application Note.
Using a general implementation, the R1 and R2
resistors allow the range of the gain to be limited;
therefore, each digital potentiometer step is a fine
adjust within that range. While in the simplified circuit,
the range is not limited, so each digital potentiometer
step causes a larger variation in the gain.
One advantage of the simplified circuit is that the RBW
and RAW resistors are of the same material so the
circuit has a very good temperature coefficient
(tempco). While in the general circuit, the tempco of the
R1 and R2 devices may not match each other or the
digital potentiometer device.
 2010 Microchip Technology Inc.
DS01316A-page 1
AN1316
Inverting Amplifier Circuit (a)
Pot1
R1
R1
R2
B
A
VIN
Non-Inverting Amplifier Circuit (b)
W
–
Pot1
W
CF (2)
–
CF (2)
Op Amp (1)
Op Amp (1)
VOUT
+
R2
B
A
VIN
VOUT
+
Note 1: A general purpose op amp, such as the MCP6001.
2: Optional feedback capacitor (CF). Used to improve circuit stability.
FIGURE 1:
Amplifier with Programmable Gain Example Circuits.
TABLE 1:
OVERVIEW OF GAIN RANGES FOR EXAMPLE CIRCUITS(1,2)
Inverting Gain (V/V)
(Figure 1a)
Configuration
R1
R2
RAB
Zero Scale
Mid Scale
Non-Inverting Gain (V/V)
(Figure 1b)
Full Scale
Zero Scale
Mid Scale
Full Scale
0
0
10k
0.00
- 1.00
- 255
1.00
2.00
256
10k
10k
10k
- 0.50
- 1.00
- 2.00
1.50
2.00
3.00
1k
10k
10k
- 0.91
- 2.50
- 20.00
1.91
3.50
21.00
10k
1k
10k
-0.50
-0.40
-1.10
1.05
1.40
2.10
Legend: Zero Scale: Wiper value = 0h, Wiper closest to Terminal B
Mid Scale: Wiper value is at mid-range value, Wiper halfway between Terminal A and Terminal B
Full Scale: Wiper value = maximum value, Wiper closest to Terminal A
Note 1: Gain calculations use an RAB resistance of the typical 10k. Gain will be effected by variation of RAB
resistance, except when R1 = R2 = 0, then RAB variation does not effect gain.
2: The calculations assume that the resistor network is configuration A (see Figure 2). This can also be
thought of as the RAB string having 2N RS resistors (even number of resistors), there the wiper can connect to Terminal B and Terminal A. At the mid-scale tap, there is an equal number of resistors (RS) above
and below that wiper setting.
DS01316A-page 2
 2010 Microchip Technology Inc.
AN1316
In Configuration A, there are 2N step resistors (RS) to
create the resistor ladder (RAB). The wiper can connect
to 2N + 1 tap points. So for an 8-bit device with 256 RS
resistors (28), the wiper decode logic requires 257
values or 9-bit decoding.
UNDERSTANDING THE DIGITAL
POTENTIOMETER’S RESISTOR
NETWORK
To understand how the digital potential will operate in
the circuit, one needs to understand how the digital
potentiometer’s resistor network is implemented.
Figure 2 shows the three general configurations of the
resistor network. Each of these configurations has
system implications.
Configuration B eliminates the top tap point, so in this
configuration there are 2N step resistors (RS) to create
the resistor ladder (RAB) and 2N wiper tap points. This
only requires 8-bit decode for the wiper logic, but does
not allow the wiper to directly connect to terminal A.
The full-scale setting is one RS element away from
terminal A.
RAB is the resistance between the resistor network’s
terminal A and terminal B. Similarly, RBW is the resistance between the resistor network’s terminal B and
the wiper terminal while RAW is the resistance between
the resistor network’s terminal A and the wiper terminal. The RS (Step) resistance is the RAB resistance
divided by the number of resistors in the RAB string.
Configuration A
A
Configuration C eliminates that top RS element so that
there are 2N - 1 step resistors (RS) to create the resistor
ladder (RAB) and 2N wiper tap points. Now the wiper
can again directly connect to terminal A, but since
there’s an odd number of RS resistors the mid-scale
wiper setting does not have an equal number or RS
resistors above and below the mid-scale tap point.
Configuration B
Configuration C
A
A
2N + 1
RW (1)
RS
RW (1)
2N - 1
RS
RAB
RS
2N
RW (1)
R
RAB S
W
1
W
1
RW (1)
RW (1)
RS
0
0
RW (1)
1
RW (1)
RS
0
RW (1)
Analog MUX
B
FIGURE 2:
RW (1)
2N - 1
RS
RW (1)
R
RAB S
W
RS
2N
RW (1)
2N - 1
RS
RW (1)
RS
2N
RW (1)
Analog MUX
B
Analog MUX
B
Resistor Network Configurations.
 2010 Microchip Technology Inc.
DS01316A-page 3
AN1316
Table 2 specifies the number of taps and RS resistors
for a given resolution for each of these configurations.
Table 3 shows the trade-off between the different
resistor network configurations.
TABLE 2:
“Bits”
# of
Taps
RS Resistors
7-bit
8-bit
Note 1:
TABLE 3:
.
MICROCHIP’S CURRENT DIGITAL POTENTIOMETER RESISTOR NETWORK
CONFIGURATIONS VS. RESOLUTIONS
Resistor Network
Configuration
Resolution
6-bit
Table 4 shows the current Microchip digital
potentiometer devices and indicates which of the
resistor network configurations they implement.
Comment
A
B
C
65 (1)
64 (1)
64
(1)
(1)
64
64
Up/Down serial interface
63
Taps
129
128 (1)
RS Resistors
128
128 (1)
127
Taps
257
256
256 (1)
RS Resistors
256
256
255 (1)
SPI and I2C™ serial interface
options
128
SPI and I2C™ serial interface
options
This resistor network configuration is not currently offered for this resolution. Future devices may be
offered in this configuration for this resolution.
RESISTOR NETWORK CONFIGURATION TRADE-OFFS
Resistor Network
Configuration
A
Number of RS resistors
Supports “true” mid-scale setting (1)
B
C
2N
2N
2N
even
even
odd
Yes
Yes
No
(3)
-1
Supports wiper connections to
terminal A and terminal B (2)
Yes
No
Number of wiper addressing bits
2N + 1
2N
2N
even
even
simple
simple
odd
Wiper addressing decode complexity
Note 1:
2:
3:
4:
complex
(4)
Yes
Equal # of RS resistors above and below mid-scale wiper tap point
This allows true zero-scale (wiper connected to terminal B) and full-scale (wiper connected to terminal A)
operation.
In this configuration there is one RS resistor between terminal A and the full-scale tap position.
This requires an extra bit for the wiper decode logic, so an 8-bit resistor network requires 9 bits of wiper
addressing.
DS01316A-page 4
 2010 Microchip Technology Inc.
AN1316
TABLE 4:
DEVICES VS. RESISTOR NETWORK CONFIGURATIONS
Resistor Network Configuration
A
Device
B
# Taps
# RS
Device
# Taps
C
# RS
Device
# Taps
# RS
MCP4131
129
129
MCP41010
256
256
MCP4011
64
63
MCP4132
MCP4141
129
129
129
129
MCP41050
MCP41100
256
256
256
256
MCP4012
MCP4013
64
64
63
63
MCP4142
MCP4151
129
257
129
257
MCP42010
MCP42050
256
256
256
256
MCP4014
MCP4017
64
128
63
127
MCP4152
MCP4161
257
257
257
257
MCP42100
256
256
MCP40D17
MCP4018
128
128
127
127
MCP4162
MCP4231
257
129
257
129
MCP40D18
MCP4019
128
128
127
127
MCP4232
MCP4241
129
129
129
129
MCP40D19
MCP4021
128
64
127
63
MCP4242
MCP4251
129
257
129
257
MCP4022
MCP4023
64
64
63
63
MCP4252
MCP4261
257
257
257
257
MCP4024
64
63
MCP4262
MCP4331
257
129
257
129
MCP4332
MCP4341
129
129
129
129
MCP4342
MCP4351
129
257
129
257
MCP4352
MCP4361
257
257
257
257
MCP4362
MCP4531
257
129
257
129
MCP4532
MCP4541
129
129
129
129
MCP4542
MCP4551
129
257
129
257
MCP4552
MCP4561
257
257
257
257
MCP4562
MCP4631
257
129
257
129
MCP4632
MCP4641
129
129
129
129
MCP4642
MCP4651
129
257
129
257
MCP4652
MCP4661
257
257
257
257
MCP4662
257
257
Legend: Devices in bold blue have multiple (2 or 4) resistor networks on the device.
 2010 Microchip Technology Inc.
DS01316A-page 5
AN1316
Potentiometer Configuration
Inverting Amplifier
When the digital potentiometer is in a potentiometer
configuration, the device is operating as a voltage
divider. As long as there is not a load on the wiper (goes
into a high-impedance input), the variation of the wiper
resistance (RW) has minimal impact on the INL and
DNL characteristics.
Figure 3 shows two implementations of an inverting
amplifier with programmable gain circuit. Circuit “a” is
the general circuit, while circuit “b” is the simplified
circuit.
Most operational amplifier programmable gain circuit
implementations utilize the digital potentiometer in the
potentiometer configuration.
Rheostat Configuration
When the digital potentiometer is in a rheostat
configuration, the device is operating as a variable
resistor. Any variation of the wiper resistance (RW)
effects the total resistance. This impacts the configurations INL and DNL characteristics. The rheostat configuration is discussed in the Alternate Implementation
section of this Application Note.
The wiper resistance is dependent on several factors
including wiper code, device VDD, terminal voltages (on
A, B and W), and temperature. Also for the same
conditions, each tap selection resistance has a small
variation. This RW variation has greater effects on
some specifications (such as INL) for the smaller
resistance devices (5.0 k) compared to larger
resistance devices (100.0 k).
AMPLIFIER CIRCUIT DETAILS
This section will discuss the two types of amplifier
circuits:
• Inverting Amplifier
• Non-Inverting Amplifier
TABLE 5:
Equation 1 shows how to calculate the gain for the general circuit (Figure 3a), while Equation 2 simplifies the
equation by having R1 = R2 = 0, and shows the equation to calculate the gain for the simplified circuit
(Figure 3b).
So the gain is the negative ratio of the resistance from
the op amp output to its negative input and the
resistance from the voltage input signal source to the
op amp negative input. The gain will increase in
magnitude as the wiper moves towards terminal A, and
will decrease in magnitude as the wiper moves towards
terminal B.
The device’s wiper resistance (RW) is ignored for first
order calculations. This is due to it being in series with
the op amp input resistance and the op amp’s very
large input impedance.
The trade-offs between the general, simplified and
alternate circuit implementations are shown in Table 5.
Table 6, Table 7 and Table 8 show the theoretical gain
values for the general and simplified circuit
implementations for the different resistor network
configurations. These calculations assume that the
RAB value is the typical value, and in the general circuit
implementation R1 = R2 = RAB = 10 k.
An Excel spreadsheet is available at this application
note’s web page. This spreadsheet calculates the gain
of the general circuit for each of the three different
digital potentiometer’s Configurations (A, B and C). The
spreadsheet allows you to modify the R1, R2 and RAB
values and then see the calculated circuit gain (file
name AN1316 Gain Calculations.xls). This
spreadsheet was used for Table 6, Table 7 and Table 8.
CIRCUIT IMPLEMENTATION TRADE-OFFS
Advantages
Disadvantages
General Circuit
(Figure 3a)
• Complete control over gain range, which
determines accuracy
• Poor tempco characteristics, since R1 and
R2 are different devices
• Increases cost and board area (for R1 and
R2)
Simplified Circuit
(Figure 3b)
• Very good tempco characteristics, since
RBW and RAW are on the same silicon
• Minimizes area and cost
• Less control over gain range and accuracy
Alternate Circuit
(Figure 4c)
• Complete control over gain range, which
determines accuracy
• Very good tempco characteristics, since
RBW1A and RBW1B are on the same silicon
• More costly and increased board area (for
dual digital potentiometer device)
• More effected by changes in wiper
characteristics (rheostat configuration vs.
potentiometer configuration)
DS01316A-page 6
 2010 Microchip Technology Inc.
AN1316
Simplified Circuit (b)
General Circuit (a)
Pot1
R1
VIN
CF (2)
–
A
VIN
R2 + RBW
W
R1 + RAW
Pot1
R2
B
A
RAW
B
RBW
W
Op Amp (1)
CF (2)
Op Amp (1)
VOUT
+
–
+
VOUT
Note 1: A general purpose op amp, such as the MCP6001.
2: Optional feedback capacitor (CF). Used to improve circuit stability.
FIGURE 3:
Inverting Amplifier with Programmable Gain Example Circuits.
EQUATION 1:
CIRCUIT GAIN EQUATION – INVERTING AMPLIFIER GENERAL CIRCUIT
R2 + RBW
VOUT = —
R1 + RAW
x VIN
Where:
RBW =
RAW =
RAB
# of Resistors
x Wiper Code
RAB
# of Resistors
EQUATION 2:
x (# of Resistors — Wiper Code)
CIRCUIT GAIN EQUATION – INVERTING AMPLIFIER SIMPLIFIED CIRCUIT
VOUT = —
RBW
RAW
x VIN
Where:
RBW =
RAW =
RAB
# of Resistors
RAB
# of Resistors
So:
VOUT = —
x Wiper Code
x (# of Resistors — Wiper Code)
Wiper Code
# of Resistors — Wiper Code
 2010 Microchip Technology Inc.
x VIN
DS01316A-page 7
AN1316
ALTERNATE IMPLEMENTATION
The drawback of this implementation is that a dual
resistor network device is more costly than a single
resistor device. Table 5 shows some trade-offs with this
circuit implementation.
Figure 4 shows an implementation which takes the
best of the general and simplified implementations. In
this implementation, a digital potentiometer with two (or
more) resistor networks is used. This allows each resistor for the gain to be individually controlled. Since both
resistors are on the same silicon, the gain resistors
have good tempco matching characteristics. With the
wipers of each resistor network tied together, the wiper
voltage will be the same. Therefore, the wiper
resistance characteristics of the two resistor networks
should be similar.
Alternate Circuit (c)
Pot1A (3)
B
VIN
RBW1A
A
W
Pot1B (3)
A
B RBW1B
W
–
CF (2)
Op Amp (1)
VOUT
+
Note 1: A general purpose op amp, such as the MCP6001.
2:
Optional feedback capacitor (CF). Used to improve circuit stability.
3:
Connecting the wiper to terminal A ensures that as the wiper register value increases, the RBW resistance
increases.
FIGURE 4:
DS01316A-page 8
Inverting Amplifier with Programmable Gain Example Circuit.
 2010 Microchip Technology Inc.
AN1316
EXAMPLE GAIN CALCULATIONS –
INVERTING AMPLIFIER
Table 6 shows a comparison of the amplifier gain
between the circuits (Figure 3a and Figure 3b) for
digital potentiometer’s resistor networks in the
Configuration A (see Figure 2) implementation. Table 6
utilized a digital potentiometer with 8-bit resolution and
with an RAB resistance = 10 k. For the general
amplifier circuit, when R1 = R2 = 10 k, the circuit’s
gain (V/V) ranged between -0.5 and -2.0. But when the
simplified circuit is used (effectively having R1 = R2 =
0) the circuit’s gain range is approximately between 0
and  (at wiper code = 255, gain = -255).
Table 7 shows a comparison of the amplifier gain
between the circuits (Figure 3a and Figure 3b) for
digital potentiometer’s resistor networks in the
Configuration B (see Figure 2) implementation. Table 7
utilized a digital potentiometer with 8-bit resolution and
with an RAB resistance = 10 k. For the general amplifier circuit, when R1 = R2 = 10 k, the circuit’s gain (V/
V) ranged between -0.5 and -1.99. But when the simplified circuit is used (effectively having R1 = R2 = 0) the
circuit’s gain range is approximately between 0 and
> -255.
 2010 Microchip Technology Inc.
Table 8 shows a comparison of the amplifier gain
between the circuits (Figure 3a and Figure 3b) for
digital potentiometer’s resistor networks in the
Configuration C (see Figure 2) implementation. Table 8
utilized a digital potentiometer with 7-bit resolution and
with an RAB resistance = 10 k. For the general
amplifier circuit, when R1 = R2 = 10 k, the circuit’s
gain (V/V) ranged between -0.5 and -2.0. But when the
simplified circuit is used (effectively having R1 = R2 =
0) the circuit’s gain range is approximately between 0
and  (at wiper code = 126, gain = -126).
Therefore, regardless of the resistor network
configuration, finer calibration of the circuit is possible
with the general circuit, but with a narrower range. Also,
resistor network configurations that allow the full-scale
setting to connect to terminal A (Configurations A and
C) can have very large magnitude gains (approximately
) since the RAW resistance is almost 0.
DS01316A-page 9
AN1316
TABLE 6:
INVERTING AMPLIFIER GAIN VS. WIPER CODE AND RW – CONFIGURATION A
Wiper Code(7)
# of
Taps
# of
Resistors
257
256
Note 1:
2:
3:
4:
5:
6:
7:
Gain (RAB = 10 k) (V/V)
General Circuit (2, 3)
Comment
Dec
Hex
Simplified
Circuit (1)
0
000h
0.0000
- 0.5556
- 0.5000
- 0.4545
1
001h
- 0.0039
- 0.5583
- 0.5029
- 0.4577
2
002h
- 0.0079
- 0.5610
- 0.5059
- 0.4608
3
003h
- 0.0119
- 0.5637
- 0.5088
- 0.4639
4
004h
- 0.0159
- 0.5664
- 0.5118
- 0.4670
:
:
:
:
:
:
:
:
:
:
:
:
126
07Eh
- 0.9692
- 0.9911
- 0.9896
- 0.9883
127
07Fh
- 0.9845
- 0.9955
- 0.9948
- 0.9942
128
080h
- 1.0000
- 1.0000
- 1.0000
- 1.0000
129
081h
- 1.0157
- 1.0045
- 1.0052
- 1.0059
130
082h
- 1.0317
- 1.0090
- 1.0105
- 1.0118
:
:
:
:
:
:
:
:
:
:
:
:
252
0FCh
- 63.0000
- 1.7654
- 1.9538
- 2.1411
253
0FDh
- 84.3333
- 1.7740
- 1.9653
- 2.1556
254
0FEh
- 127.0000
- 1.7826
- 1.9767
- 2.1703
255
0FFh
- 255.0000
- 1.7913
- 1.98883
- 2.1851
256
100h
Divide Error (4)
- 1.8000
- 2.0000
- 2.2000
@ RAB(MIN)
(5)
@ RAB(TYP)
@ RAB(MAX)
(6)
Zero Scale
Mid Scale
Full Scale
Gain = - ((RAB/# of Resistors) * Wiper Code)/
((RAB/# of Resistors) * (# of Resistors - Wiper Code)) = - (Wiper Code)/(# of Resistors - Wiper Code)
Gain = - (R2 + RS * (Wiper Code))/(R1 + RS * (# of Resistors - Wiper Code)
Uses R1 = R2 = 10 k.
Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
The RAB(MIN) shows the narrowest range of gain (more accuracy per wiper code step). Ensure gain range
is adequate.
The RAB(MAX) shows the widest range of gain (less accuracy per wiper code step). Ensure gain resolution
is adequate.
If the A and B terminals are swapped in the circuit, as the wiper value increases, the magnitude of the gain
decreases.
DS01316A-page 10
 2010 Microchip Technology Inc.
AN1316
TABLE 7:
INVERTING AMPLIFIER GAIN VS. WIPER CODE AND RW – CONFIGURATION B
Wiper Code(7)
# of
Taps
# of
Resistors
256
256
Note 1:
2:
3:
4:
5:
6:
7:
Gain (RAB = 10 k) (V/V)
General Circuit (2, 3)
Comment
Dec
Hex
Simplified
Circuit (1)
0
00h
0.0000
- 0.5556
- 0.5000
- 0.4545
1
01h
- 0.0039
- 0.5583
- 0.5029
- 0.4577
2
02h
- 0.0079
- 0.5610
- 0.5059
- 0.4608
3
03h
- 0.0119
- 0.5637
- 0.5088
- 0.4639
4
04h
- 0.0159
- 0.5664
- 0.5118
- 0.4670
:
:
:
:
:
:
:
:
:
:
:
:
126
7Eh
- 0.9692
- 0.9911
- 0.9896
- 0.9883
127
7Fh
- 0.9845
- 0.9955
- 0.9948
- 0.9942
128
80h
- 1.0000
- 1.0000
- 1.0000
- 1.0000
129
81h
- 1.0157
- 1.0045
- 1.0052
- 1.0059
130
82h
- 1.0317
- 1.0090
- 1.0105
- 1.0118
:
:
:
:
:
:
:
:
:
:
:
:
252
FCh
- 63.0000
- 1.7654
- 1.9538
- 2.1411
253
FDh
- 84.3333
- 1.7740
- 1.9653
- 2.1556
254
FEh
- 127.0000
- 1.7826
- 1.9767
- 2.1703
255
FFh
- 255.0000
- 1.7913
- 1.98883
- 2.1851
@ RAB(MIN)
(5)
@ RAB(TYP)
@ RAB(MAX)
(6)
Zero
Scale
Mid Scale
Full Scale
Gain = - ((RAB/# of Resistors) * Wiper Code)/
((RAB/# of Resistors) * (# of Resistors - Wiper Code)) = - (Wiper Code)/(# of Resistors - Wiper Code)
Gain = - (R2 + RS * (Wiper Code))/(R1 + RS * (# of Resistors - Wiper Code)
Uses R1 = R2 = 10k.
Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
The RAB(MIN) shows the narrowest range of gain (more accuracy per wiper code step). Ensure gain range
is adequate.
The RAB(MAX) shows the widest range of gain (less accuracy per wiper code step). Ensure gain resolution
is adequate.
If the A and B terminals are swapped in the circuit, as the wiper value increases, the magnitude of the gain
decreases.
 2010 Microchip Technology Inc.
DS01316A-page 11
AN1316
TABLE 8:
INVERTING AMPLIFIER GAIN VS. WIPER CODE AND RW – CONFIGURATION C
Wiper Code(7)
# of
Taps
# of
Resistors
128
127
Note 1:
2:
3:
4:
5:
6:
7:
Gain (RAB = 10 k) (V/V)
General Circuit (2, 3)
Comment
Dec
Hex
Simplified
Circuit (1)
0
00h
0.0000
- 0.5556
- 0.5000
- 0.4545
1
01h
- 0.0079
- 0.5610
- 0.5059
- 0.4608
2
02h
- 0.0160
- 0.5665
- 0.5119
- 0.4671
3
03h
- 0.0242
- 0.5721
- 0.5179
- 0.4735
4
04h
- 0.0325
- 0.5776
- 0.5240
- 0.4800
:
:
:
:
:
:
:
:
:
:
:
:
62
3Eh
- 0.9538
- 0.9866
- 0.9844
- 0.9824
63
3Fh
- 0.9844
- 0.9955
- 0.9948
- 0.9941
64
40h
- 1.0159
- 1.0045
- 1.0053
- 1.0059
65
41h
- 1.0484
- 1.0136
- 1.0159
- 1.0179
66
42h
- 1.0820
- 1.0228
- 1.0266
- 1.0300
:
:
:
:
:
:
:
:
:
:
:
:
124
7Ch
- 41.3333
- 1.7481
- 1.9308
- 2.1118
125
7Dh
- 62.5000
- 1.7652
- 1.9535
- 2.1406
126
7Eh
- 126.0000
- 1.7825
- 1.9766
- 2.1700
127
7Fh
Divide Error (4)
- 1.8000
- 2.0000
- 2.2000
@ RAB(MIN)
(5)
@ RAB(TYP)
@ RAB(MAX)
(6)
Zero Scale
Mid Scale
Full Scale
Gain = - ((RAB/# of Resistors) * Wiper Code)/
((RAB/# of Resistors) * (# of Resistors - Wiper Code)) = - (Wiper Code)/(# of Resistors - Wiper Code)
Gain = - (R2 + RS * (Wiper Code))/(R1 + RS * (# of Resistors - Wiper Code)
Uses R1 = R2 = 10 k.
Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
The RAB(MIN) shows the narrowest range of gain (more accuracy per wiper code step). Ensure gain range
is adequate.
The RAB(MAX) shows the widest range of gain (less accuracy per wiper code step). Ensure gain resolution
is adequate.
If the A and B terminals are swapped in the circuit, as the wiper value increases, the magnitude of the gain
decreases.
DS01316A-page 12
 2010 Microchip Technology Inc.
AN1316
Non-Inverting Amplifier
Figure 5 shows two implementations of an non-inverting amplifier with programmable gain circuit. Circuit “a”
is the general circuit while circuit “b” is the simplified
circuit.
Equation 3 shows how to calculate the gain for the
general circuit (Figure 5a), while Equation 4 simplifies
the equation by having R1 = R2 = 0, and shows the
equation to calculate the gain for the simplified circuit
(Figure 5b).
So the gain is the ratio of the resistance from the op
amp output to its negative input and the resistance from
the op amp’s negative input to ground. The gain will
increase in magnitude as the wiper moves towards
terminal A, and will decrease in magnitude as wiper
moves towards terminal B.
TABLE 9:
The device’s wiper resistance (RW) is ignored for first
order calculations. This is due to it being in series with
the op amp input resistance and the op amp’s very
large input impedance.
Trade-offs between the general, simplified and
alternate circuit implementations are the same tradeoffs as the inverting amplifier circuit. These trade-offs
are shown in Table 9.
Table 10, Table 11 and Table 12 show the theoretical
gain values for the general and simplified circuit
implementations for the different resistor network
configurations. These calculations assume that the
RAB value is the typical value, and in the general circuit
implementation R1 = R2 = RAB = 10 k.
An Excel spreadsheet is available at this application
note’s web page. This spreadsheet calculates the gain
of the general circuit for each of the three different digital potentiometer’s Configurations (A, B and C). The
spreadsheet allows you to modify the R1, R2 and RAB
values and then see the calculated circuit gain (file
name AN1316 Gain Calculations.xls). This
spreadsheet was used for Table 10, Table 11 and
Table 12.
CIRCUIT IMPLEMENTATION TRADE-OFFS
Advantages
Disadvantages
General Circuit
(Figure 5a)
• Complete control over gain range, which
determines accuracy
• Poor tempco characteristics, since R1 and
R2 are different devices
• Increases cost and board area (for R1 and
R2)
Simplified Circuit
(Figure 5b)
• Very good tempco characteristics, since
RBW and RAW are on the same silicon
• Minimizes area and cost
• Less control over gain range and accuracy
Alternate Circuit
(Figure 6c)
• Complete control over gain range, which
determines accuracy
• Very good tempco characteristics, since
RBW1A and RBW1B are on the same silicon
• More costly and increased board area (for
dual digital potentiometer device)
• More effected by changes in wiper
characteristics (rheostat configuration vs.
potentiometer configuration)
 2010 Microchip Technology Inc.
DS01316A-page 13
AN1316
Simplified Circuit (b)
General Circuit (a)
Pot1
R1
B
A
–
B
A
R2 + RBW
W
R1 + RAW
Pot1
R2
CF (2)
RAW
W
–
Op Amp (1)
VIN
+
RBW
CF (2)
Op Amp (1)
VOUT
VIN
+
VOUT
Note 1: A general purpose op amp, such as the MCP6001.
2: Optional feedback capacitor (CF). Used to improve circuit stability.
FIGURE 5:
Non-Inverting Amplifier with Programmable Gain Example Circuits.
EQUATION 3:
CIRCUIT GAIN EQUATION – NON-INVERTING AMPLIFIER GENERAL CIRCUIT
R2 + RBW
VOUT =
R1 + RAW
+ 1 x VIN
Where:
RAB
RBW =
# of Resistors
RAW =
RAB
# of Resistors
EQUATION 4:
x Wiper Code
x (# of Resistors — Wiper Code)
CIRCUIT GAIN EQUATION – NON-INVERTING AMPLIFIER SIMPLIFIED CIRCUIT
VOUT =
RBW
RAW
+ 1 x VIN
Where:
RBW =
RAW =
RAB
# of Resistors
RAB
# of Resistors
So:
VOUT =
x Wiper Code
x (# of Resistors — Wiper Code)
Wiper Code
(# of Resistors — Wiper Code)
DS01316A-page 14
+1
x VIN
 2010 Microchip Technology Inc.
AN1316
ALTERNATE IMPLEMENTATION
The drawback of this implementation is that a dual
resistor network device is more costly then a single
resistor device. Table 9 shows the trade-offs with this
circuit implementation.
Figure 6 shows an implementation which takes the
best of the general and simplified implementations. In
this implementation, a digital potentiometer with two (or
more) resistor networks is used. This allows each resistor for the gain to be individually controlled. Since both
resistors are on the same silicon, the gain resistors
have good tempco matching characteristics. With the
wipers of each resistor network tied together, the wiper
voltage will be the same. Therefore, the wiper resistance characteristics of the two resistor networks
should be similar.
Alternate Circuit
Pot1A (3)
B
RBW1A
W
A
Pot1B (3)
B RBW1B
A
W
–
CF (2)
Op Amp (1)
VIN
+
VOUT
Note 1: A general purpose op amp, such as the MCP6001.
FIGURE 6:
2:
Optional feedback capacitor (CF). Used to improve circuit stability.
3:
Connecting the wiper to terminal A ensure that as the wiper register value increases, the RBW resistance
increases.
Non-Inverting Amplifier with Programmable Gain Example Circuit.
 2010 Microchip Technology Inc.
DS01316A-page 15
AN1316
EXAMPLE GAIN CALCULATIONS –
NON-INVERTING AMPLIFIER
Table 10 shows a comparison of the amplifier gain
between the circuits (Figure 5a and Figure 5b) for
digital potentiometer’s resistor networks in the Configuration A (see Figure 2) implementation. Table 10
utilized digital potentiometer with 8-bit resolution and
with an RAB resistance = 10 k. For the general
amplifier circuit, when R1 = R2 = 10 k, the circuit’s
gain (V/V) ranged between 1.5 and 3.0. But when the
simplified circuit is used (effectively having R1 = R2 =
0) the circuit’s gain range is approximately between 1
and  (at wiper code = 255, gain = 256).
Table 11 shows a comparison of the amplifier gain
between the circuits (Figure 5a and Figure 5b) for
digital potentiometer’s resistor networks in the Configuration B (see Figure 2) implementation. Table 11
utilized a digital potentiometer with 8-bit resolution and
with an RAB resistance = 10 k. For the general
amplifier circuit, when R1 = R2 = 10 k, the circuit’s
gain (V/V) ranged between 1.5 and 2.99. But when the
simplified circuit is used (effectively having R1 = R2 =
0) the circuit’s gain range is between 1 and > 255.
DS01316A-page 16
Table 12 shows a comparison of the amplifier gain
between the circuits (Figure 5a and Figure 5b) for
digital potentiometer’s resistor networks in the Configuration C (see Figure 2) implementation. Table 12
utilized a digital potentiometer with 7-bit resolution and
with an RAB resistance = 10 k. For the general
amplifier circuit, when R1 = R2 = 10 k, the circuit’s
gain (V/V) ranged between 1.5 and 3.0. But when the
simplified circuit is used (effectively having R1 = R2 =
0) the circuit’s gain range is approximately between 1
and  (at wiper code = 126, gain = 127).
Therefore, regardless of the resistor network
configuration, finer calibration of the circuit is possible
with the general circuit, albeit with a narrower range.
Also, resistor network configurations that allow the fullscale setting to connect to terminal A (Configurations A
and C) can have very large magnitude gains
(approximately ) since the RAW resistance is almost 0.
 2010 Microchip Technology Inc.
AN1316
TABLE 10:
NON-INVERTING AMPLIFIER GAIN VS. WIPER CODE AND RW – CONFIGURATION A
Wiper Code(7)
# of
Taps
# of
Resistors
257
256
2:
3:
4:
5:
6:
7:
General Circuit (2, 3)
Comment
Dec
Hex
Simplified
Circuit (1)
0
000h
1.0000
1.5556
1.5000
1.4545
1
001h
1.0039
1.5583
1.5029
1.4577
2
002h
1.0079
1.5610
1.5059
1.4608
3
003h
1.0119
1.5637
1.5088
1.4639
4
004h
1.0159
1.5664
1.5118
1.4670
:
:
:
:
:
:
:
:
:
:
:
:
126
07Eh
1.9692
1.9911
1.9896
1.9883
127
07Fh
1.9845
1.9955
1.9948
1.9942
128
080h
2.0000
2.0000
2.0000
2.0000
129
081h
2.0157
2.0045
2.0052
2.0059
130
082h
2.0317
2.0090
2.0105
2.0118
:
:
:
:
:
:
:
:
:
:
:
:
252
0FCh
64.0000
2.7654
2.9538
3.1411
253
0FDh
85.3333
2.7740
2.9653
3.1556
254
0FEh
128.0000
2.7826
2.9767
3.1703
255
0FFh
256.0000
2.7913
2.98883
3.1851
2.8000
3.0000
3.2000
256
Note 1:
Gain (RAB = 10 k) (V/V)
100h
Divide Error
(4)
@ RAB(MIN)
(5)
@ RAB(TYP)
@ RAB(MAX)
(6)
Zero Scale
Mid Scale
Full Scale
Gain = - ((RAB/# of Resistors) * Wiper Code)/
((RAB/# of Resistors) * (# of Resistors - Wiper Code)) = - (Wiper Code) /(# of Resistors - Wiper Code)
Gain = - (R2 + RS * (Wiper Code))/(R1 + RS * (# of Resistors - Wiper Code)
Uses R1 = R2 = 10 k.
Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
The RAB(MIN) shows the narrowest range of gain (more accuracy per wiper code step). Ensure gain range
is adequate.
The RAB(MAX) shows the widest range of gain (less accuracy per wiper code step). Ensure gain resolution
is adequate.
If the A and B terminals are swapped in the circuit, as the wiper value increases, the gain decreases.
 2010 Microchip Technology Inc.
DS01316A-page 17
AN1316
TABLE 11:
NON-INVERTING AMPLIFIER GAIN VS. WIPER CODE AND RW – CONFIGURATION B
Wiper Code(7)
# of
Taps
# of
Resistors
256
256
Note 1:
2:
3:
4:
5:
6:
7:
Gain (RAB = 10 k) (V/V)
General Circuit (2,3)
Comment
Dec
Hex
Simplified
Circuit (1)
0
00h
1.0000
1.5556
1.5000
1.4545
1
01h
1.0039
1.5583
1.5029
1.4577
2
02h
1.0079
1.5610
1.5059
1.4608
@ RAB(MIN)
(5)
@ RAB(TYP)
@ RAB(MAX)
3
03h
1.0119
1.5637
1.5088
1.4639
4
04h
1.0159
1.5664
1.5118
1.4670
:
:
:
:
:
:
:
:
:
:
:
:
126
7Eh
1.9692
1.9911
1.9896
1.9883
127
7Fh
1.9845
1.9955
1.9948
1.9942
128
80h
2.0000
2.0000
2.0000
2.0000
129
81h
2.0157
2.0045
2.0052
2.0059
130
82h
2.0317
2.0090
2.0105
2.0118
:
:
:
:
:
:
:
:
:
:
:
:
252
FCh
- 63.0000
2.7654
2.9538
3.1411
253
FDh
- 84.3333
2.7740
2.9653
3.1556
254
FEh
- 127.0000
2.7826
2.9767
3.1703
255
FFh
- 255.0000
2.7913
2.98883
3.1851
(6)
Zero
Scale
Mid Scale
Full Scale
Gain = - ((RAB/# of Resistors) * Wiper Code)/
((RAB/# of Resistors) * (# of Resistors - Wiper Code)) = - (Wiper Code)/(# of Resistors - Wiper Code)
Gain = - (R2 + RS * (Wiper Code))/(R1 + RS * (# of Resistors - Wiper Code)
Uses R1 = R2 = 10 k.
Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
The RAB(MIN) shows the narrowest range of gain (more accuracy per wiper code step). Ensure gain range
is adequate.
The RAB(MAX) shows the widest range of gain (less accuracy per wiper code step). Ensure gain resolution
is adequate.
If the A and B terminals are swapped in the circuit, as the wiper value increases, the gain decreases.
DS01316A-page 18
 2010 Microchip Technology Inc.
AN1316
TABLE 12:
INVERTING AMPLIFIER GAIN VS. WIPER CODE AND RW – CONFIGURATION C
Wiper Code(7)
# of
Taps
# of
Resistors
128
127
Note 1:
2:
3:
4:
5:
6:
7:
Gain (RAB = 10 k) (V/V)
Dec
Hex
Simplified
Circuit (1)
0
00h
1.0000
General Circuit (2, 3)
@ RAB(MIN)
(5)
@ RAB(TYP)
1.5556
1.5000
Comment
@ RAB(MAX)
1.4545
1
01h
1.0079
1.5610
1.5059
1.4608
2
02h
1.0160
1.5665
1.5119
1.4671
3
03h
1.0242
1.5721
1.5179
1.4735
4
04h
1.0325
1.5776
1.5240
1.4800
:
:
:
:
:
:
:
:
:
:
:
:
62
3Eh
1.9538
1.9866
1.9844
1.9824
63
3Fh
1.9844
1.9955
1.9948
1.9941
64
40h
2.0159
2.0045
2.0053
2.0059
65
41h
2.0484
2.0136
2.0159
2.0179
66
42h
2.0820
2.0228
2.0266
2.0300
:
:
:
:
:
:
:
:
:
:
:
:
124
7Ch
42.3333
2.7481
2.9308
3.1118
125
7Dh
63.5000
2.7652
2.9535
3.1406
126
7Eh
127.0000
2.7825
2.9766
3.1700
127
7Fh
Divide Error (4)
2.8000
3.0000
3.2000
(6)
Zero Scale
Mid Scale
Full Scale
Gain = - ((RAB/# of Resistors) * Wiper Code)/
((RAB/# of Resistors) * (# of Resistors - Wiper Code)) = - (Wiper Code)/(# of Resistors - Wiper Code)
Gain = - (R2 + RS * (Wiper Code))/(R1 + RS * (# of Resistors - Wiper Code)
Uses R1 = R2 = 10 k.
Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
The RAB(MIN) shows the narrowest range of gain (more accuracy per wiper code step). Ensure gain range
is adequate.
The RAB(MAX) shows the widest range of gain (less accuracy per wiper code step). Ensure gain resolution
is adequate.
If the A and B terminals are swapped in the circuit, as the wiper value increases, the gain decreases.
 2010 Microchip Technology Inc.
DS01316A-page 19
AN1316
OPTIMIZING TEMPERATURE
BEHAVIOR
Figure 7 shows general implementations of the
non-inverting amplifier with programmable gain. Two of
the circuits use fixed resistors R1 and R2 or only R1,
while the other implementations only use digital
potentiometers, either a single or dual device.
The topology of the programmable gain circuit
determines how the circuit will be affected by variations
in temperature as well as the manufacturing process
variation of the digital potentiometer.
In these circuits, for our calculations we will use
R1 = 1172, R2 = 1172. We chose this value to aid in
the comparison of the implementations, since in circuit (d)
it needed to be an expected RBW value. So using an 8-bit
device with the typical RAB value of 100 k, this gives a
Step Resistance (RS) of 391. Using a wiper code of 3,
gives an RBW resistance of 1172, assuming that RW =
0. You may re-evaluate these values with assumptions
based on your conditions. An Excel spreadsheet is
available at this application note’s web page, which
allows you to modify the R1, R2 and RAB values and then
see the circuit gain and range of gain error (file name
Table 1-13 Gain Calculations.xls).
The gain circuit topology will effect the behavior of the
circuit. Devices with multiple resistors, that are not of
the same silicon, have variations due to the different
temperature coefficient of the resistive devices (circuits
(a) and (b)). These circuits also will have variations due
to the variation of the RAB resistance due to process
(±20%). So one needs to understand the application’s
requirements to determine if the selected circuit meets
those requirements.
For this discussion, Figure 7 shows the circuit options,
while Table 13 compares characteristics for these
circuits.
General Circuit (b)
General Circuit (a)
Pot1
R1
B
A
R1 + RAW
W
RBW1A + R2
–
Pot1
R1
R2
Op Amp (1)
VOUT
+
Simplified Circuit (c)
VIN
Alternate Circuit (d1)
Pot1B (3)
Pot1
A
RAW
RBW
–
+
RBW1B
CF (2)
Op Amp (1)
VIN
Pot1A (3)
B RBW1A
A
W
W
CF (2)
Op Amp (1)
VOUT
3: The connection of the wiper to
terminal A is optional, but evaluation
of the trade-offs should be done for
the specific application requirements.
This is due to the variation of the effective
wiper resistance over wiper code.
RW(EFF) = RW || (# RS - Wiper Code) * RS
4: Orientation of the digital potentiometers
for best performance is dependent on the
voltage levels expected for the VOUT pin
and the op amps “-” input pin. The Blue
lines/text vs. Red lines/text indicates the
two orientations.
DS01316A-page 20
VOUT
+
–
Note 1: A general purpose op amp, such
as the MCP6001.
2: Optional feedback capacitor (CF).
Used to improve circuit stability.
FIGURE 7:
A
B
B
W
CF (2)
–
Op Amp (1)
VIN
RBW1A
W
R1
CF (2)
B
A
VIN
+
VOUT
Alternate Circuit (d2 (3))
Pot1B (3)
A
RBW1B
B
W
Pot1A (3, 4)
A
B
B
A
RBW1A
W
–
CF (2)
Op Amp (1)
The connection selected should
optimize the voltage range on
the W pin to keep the digital
potentiometers analog switch
in the active range. This minimizes
the RW resistance.
VIN
+
VOUT
Non-Inverting Amplifier with Programmable Gain Example Circuits.
 2010 Microchip Technology Inc.
AN1316
TABLE 13:
NON-INVERTING AMPLIFIER WITH PROGRAMMABLE GAIN CIRCUIT COMPARISON
Programmable Gain (V/V)
RAB () (2)
Circuit
Wiper
Code
(a)
(b)
(c) (3)
(d)
(4)
RBW ()
3
1,172
128
50,000
255
99,609
3
1,172
128
50,000
255
99,609
3
1,172
128
50,000
255
99,609
3
1,172
128
50,000
255
99,609
Gain (1) (VOUT / VIN)
Temperature
Error
(ppm / °C)
Variation (1)
(%)
Tempco
(ppm/°C)
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
± 20%
100
2.800
3.000
3.200
6.66
100
100
36.130
44.662
53.195
19.10
100
100
69.993
86.991
103.989
19.54
100
100
1.800
2.000
2.200
10.00
100
Min.
Typ.
Max.
Range
Error (%)
100
35.130
43.662
52.195
19.54
100
100
68.993
85.991
102.989
19.77
100
100
1.012
1.012
1.012
0.00
<1
100
2.000
2.000
2.000
0.00
<1
100
256.000
256.000
256.000
0.00
<1
100
2.000
2.000
2.000
0.00
<1
100
43.667
43.667
43.667
0.00
<1
100
856.000
856.000
856.000
0.00
<1
Note 1: Assuming RW = 0. for Configuration (a): R1 = R2 = 1,172 and for Configuration (b):
RBW1B = 1,172.
2: Typical RAB resistance is 100 k.
3: The gain is a ratio of the wiper tap position, so the actual RAB resistance has no effect on the gain.
4: Since both RBW1A and RBW1B resistors are on the same process, there variations match each other. Since
the matching of the one pot to the other is typically 1.00%, then the range error will have a maximum error
of 1.00%.
 2010 Microchip Technology Inc.
DS01316A-page 21
AN1316
THE FEEDBACK CAPACITOR (CF)
SUMMARY
The feedback capacitor (CF) is used to stabilize the
gain circuit. Initial evaluation of the feedback capacitor
value can be done by applying a step input signal on
the VIN signal.
This application note has discussed circuit
implementations and characteristics for programmable
amplifier gain circuits that should be understood when
using a digital potentiometer in these circuits. Digital
potentiometers are a good fit for these circuits,
especially with respect to gain programmability and
tempco characteristics.
As the CF value increases, the rise and fall times of the
VOUT signal will increase, but the overshoot and ringing
of the VOUT signal will decrease.
As the CF value decreases, the rise and fall times of the
VOUT signal will decrease, but the overshoot and
ringing of the VOUT signal will increase.
To optimize the CF value, try the step input signal
across the wiper code range for the application. So test
the input step at your application’s gain limits.
CONTROLLING THE DIGITAL
POTENTIOMETER
Digital potentiometers are offered with different interfaces. Microchip offered devices with SPI, I2C and Up/
Down interfaces. SPI and I2C interfaces allow the wiper
to be updated with any wiper value, while the Up/Down
interface requires that the wiper be sequenced through
the range to get to the desired position.
Table 14 shows the available digital potentiometer
development boards and if the board includes application firmware. For more information visit our web site at
www.microchip.com/analogtools.
TABLE 14:
MCP402XEV
MCP4XXXDM-DB
Interface
Includes
Code ?
U/D
Yes
SPI
Yes
MCP42XXDM-PTPLS
SPI (1, 2)
Yes
MCP46XXDM-PTPLS
I2C™ (1, 2)
Yes
SPI
No (2)
MCP42XXEV (4)
MCP43XXEV (3)
SPI
No (2)
(4)
I2C™
No (2)
MCP401XEV (3)
I2C™
No (2)
Note 1:
2:
3:
4:
Using this information and the supplied Excel
spreadsheets, the programmable gain circuit can be
optimized for the applications gain and temperature
response requirements.
REVISION HISTORY
Rev A (April 2010)
Initial release.
DEVELOPMENT TOOL
SUPPORT
Order Number
MCP46XXEV
The topology of the programmable gain circuit
determines how the circuit will be affected by variations
in temperature as well as the manufacturing process
variation of the digital potentiometer. It is also important
to understand how the selected resistor networks
configuration affects the circuits operation. Depending
on your need, Microchip offers a wide range of devices.
For more information contact your local sales representative or visit our web site at www.microchip.com.
Requires a PICDEM™ board with the
PICtail™ Plus interface. Code was
developed for the PIC24FJ128GA010.
Demos use the PICkit™ Serial Interface
to control the device operation.
Expected Availability, April 2010.
Expected Availability May 2010.
DS01316A-page 22
 2010 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC,
KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART,
PIC32 logo, rfPIC and UNI/O are registered trademarks of
Microchip Technology Incorporated in the U.S.A. and other
countries.
FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor,
MXDEV, MXLAB, SEEVAL and The Embedded Control
Solutions Company are registered trademarks of Microchip
Technology Incorporated in the U.S.A.
Analog-for-the-Digital Age, Application Maestro, CodeGuard,
dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN,
ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial
Programming, ICSP, Mindi, MiWi, MPASM, MPLAB Certified
logo, MPLIB, MPLINK, mTouch, Octopus, Omniscient Code
Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit,
PICtail, REAL ICE, rfLAB, Select Mode, Total Endurance,
TSHARC, UniWinDriver, WiperLock and ZENA are
trademarks of Microchip Technology Incorporated in the
U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated
in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2010, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 978-1-60932-133-8
Microchip received ISO/TS-16949:2002 certification for its worldwide
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Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
 2010 Microchip Technology Inc.
DS01316A-page 23
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DS01316A-page 24
 2010 Microchip Technology Inc.
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