• Low Power and Supply Voltages:
: 300 µA/amplifier (typical)
-I
Q
- Wide Supply Voltage Range: 1.8V to 5.5V
• Easy to Use:
- Rail-to-Rail Input/Output
- Gain Bandwidth Product: 1.3 MHz (typical)
- Unity Gain Stable
- Available in Single and Dual
- Single with Chip Select (CS
): MCP6V08
• Extended Temperature Range: -40°C to +125°C
Typical Applications
• Portable Instrumentation
• Sensor Conditioning
• Temperature Measurement
• DC Offset Correction
• Medical Instrumentation
Description
The Microchip Technology Inc. MCP6V06/7/8 family of
operational amplifiers has input offset voltage
correction for very low offset and offset drift. These
devices have a wide gain bandwidth product (1.3 MHz,
typical) and strongly reject switching noise. They are
unity gain stable, have no 1/f noise, and have good
PSRR and CMRR. These products operate with a
single supply voltage as low as 1.8V, while drawing
300 µA/amplifier (typical) of quiescent current.
The Microchip Technology Inc. MCP6V06/7/8 op amps
are offered in single (MCP6V06), single with Chip
Select (CS
Current at Input Pins ....................................................±2 mA
Analog Inputs (V
All other Inputs and Outputs ............ V
Difference Input voltage ...................................... |V
+ and VIN–) †† ... VSS– 1.0V to VDD+1.0V
IN
– 0.3V to VDD+0.3V
SS
DD–VSS
Output Short Circuit Current .................................Continuous
Current at Output and Supply Pins ............................±30 mA
Storage Temperature ....................................-65°C to +150°C
|
† Notice: Stresses above those listed under “Absolute
Maximum Ratings” may cause permanent damage to the
device. This is a stress rating only and functional operation of
the device at those or any other conditions above those
indicated in the operational listings of this specification is not
implied. Exposure to maximum rating conditions for extended
periods may affect device reliability.
†† See Section 4.2.1 “Rail-to-Rail Inputs”.
Max. Junction Temperature ........................................+150°C
ESD protection on all pins (HBM, MM) ................≥ 4 kV, 300V
1.2Specifications
TABLE 1-1:DC ELECTRICAL SPECIFICATIONS
Electrical Characteristics: Unless otherwise indicated, TA = +25°C, VDD = +1.8V to +5.5V, VSS = GND, VCM = VDD/3,
V
OUT=VDD
Input Offset
Input Offset VoltageV
Input Offset Voltage Drift with Temperature
(linear Temp. Co.)
Input Offset Voltage Quadratic Temp. Co.TC
Power Supply RejectionPSRR125142—dB(Note 1)
Input Bias Current and Impedance
Input Bias CurrentI
Input Bias Current across TemperatureI
Input Offset CurrentI
Input Offset Current across TemperatureI
Common Mode Input ImpedanceZ
Differential Input ImpedanceZ
Common Mode
Common-Mode Input Voltage RangeV
Common-Mode RejectionCMRR120136—dBV
Open-Loop Gain
DC Open-Loop Gain (large signal)A
Note 1:Set by design and characterization. Due to thermal junction and other effects in the production environment, these
/2, VL=VDD/2, RL = 20 kΩ to VL, and CS = GND (refer to Figure 1-5 and Figure 1-6).
ParametersSymMinTypMaxUnitsConditions
OS
TC
1
2
B
B
I
B
OS
OS
I
OS
CM
DIFF
CMRVSS
CMRR130147—dBV
OL
A
OL
parts can only be screened in production (except TC
2:Figure 2-18 shows how V
changed across temperature for the first three production lots.
FIGURE 1-6:AC and DC Test Circuit for
Most Inverting Gain Conditions.
The circuit in Figure 1-7 tests the op amp input’s
dynamic behavior (i.e., IMD, t
potentiometer balances the resistor network (V
should equal V
at DC). The op amp’s common
REF
STR
, t
STL
and t
ODR
). The
OUT
mode input voltage is VCM=VIN/2. The error at the
input (V
) appears at V
ERR
with a noise gain of
OUT
10 V/V.
FIGURE 1-7:Test Circuit for Dynamic
Input Behavior.
MCP6V06/7/8
0%
2%
4%
6%
8%
10%
12%
14%
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
Input Offset Voltage (µV)
Percentage of Occurrences
80 Samples
T
A
= +25°C
V
DD
= 1.8V and 5.5V
Soldered on PCB
0%
5%
10%
15%
20%
25%
-50
-40
-30
-20
-10
0
10
20
30
40
50
Input Offset Voltage Drift; TC1 (nV/°C)
Percentage of Occurrences
80 Samples
V
DD
= 1.8V and 5.5V
Soldered on PCB
0%
5%
10%
15%
20%
25%
30%
-0.4
-0.2
0.0
0.2
0.4
Input Offset Voltage's Quadratic Temp Co;
TC
2
(nV/°C2)
Percentage of Occurrences
80 Samples
V
DD
= 1.8V and 5.5V
Soldered on PCB
-4
-3
-2
-1
0
1
2
3
4
0.00.51.01.52.02.53.03.54.04.55.05.56.06.5
Power Supply Voltage (V)
Input Offset Voltage (µV)
+125°C
+85°C
+25°C
-40°C
VCM = V
CMR_L
Representative Part
-4
-3
-2
-1
0
1
2
3
4
0.00.51.01.52.02.53.03.54.04.55.05.56.06.5
Power Supply Voltage (V)
Input Offset Voltage (µV)
+125°C
+85°C
+25°C
-40°C
VCM = V
CMR_H
Representative Part
-4
-3
-2
-1
0
1
2
3
4
0.00.51.01.52.02.53.03.54.04.55.05.5
Output Voltage (V)
Input Offset Voltage (µV)
VDD = 1.8V
VDD = 5.5V
Representative Part
2.0TYPICAL PERFORMANCE CURVES
Note:The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore outside the warranted range.
Note: Unless otherwise indicated, TA= +25°C, VDD= +1.8V to 5.5V, VSS= GND, VCM=VDD/3, V
V
FIGURE 2-61:Quiescent Current in
Shutdown vs. Power Supply Voltage.
V
V
MCP6V06/7/8
3.0PIN DESCRIPTIONS
Descriptions of the pins are listed in Table 3-1.
TABLE 3-1:PIN FUNCTION TABLE
MCP6V06MCP6V07MCP6V08
SOICDFN, SOICSOIC
616V
222V
333V
444VSSNegative Power Supply
—5—V
—6—V
—7—V
787V
—— 8 CS
1, 5, 8—1, 5NCNo Internal Connection
SymbolDescription
, V
OUT
OUTA
–, V
IN
INA
+, V
IN
INA
+Non-inverting Input (op amp B)
INB
–Inverting Input (op amp B)
INB
OUTB
DD
Output (op amp A)
–Inverting Input (op amp A)
+Non-inverting Input (op amp A)
Output (op amp B)
Positive Power Supply
Chip Select (op amp A)
3.1Analog Outputs
The analog output pins (V
voltage sources.
) are low-impedance
OUT
3.2Analog Inputs
The non-inverting and inverting inputs (VIN+, VIN–, …)
are high-impedance CMOS inputs with low bias
currents.
3.3Power Supply Pins
The positive power supply (VDD) is 1.8V to 5.5V higher
than the negative power supply (VSS). For normal
operation, the other pins are between VSS and VDD.
Typically, these parts are used in a single (positive)
supply configuration. In this case, V
ground and VDD is connected to the supply. VDD will
need bypass capacitors.
is connected to
SS
3.4Chip Select (CS) Digital Input
This pin (CS) is a CMOS, Schmitt-triggered input that
places the MCP6V08 op amps into a low power mode
of operation.
The MCP6V06/7/8 family of auto-zeroed op amps is
manufactured using Microchip’s state of the art CMOS
process. It is designed for low cost, low power and high
precision applications. Its low supply voltage, low
quiescent current and wide bandwidth makes the
MCP6V06/7/8 ideal for battery-powered applications.
4.1Overview of Auto-zeroing
Operation
Figure 4-1 shows a simplified diagram of the
MCP6V06/7/8 auto-zeroed op amps. This will be used
to explain how the DC voltage errors are reduced in this
architecture.
FIGURE 4-1:Simplified Auto-zeroed Op Amp Functional Diagram.
4.1.1BUILDING BLOCKS
The Null Amp. and Main Amp. are designed for high
FW
gain and accuracy using a differential topology. They
have an auxiliary input (bottom left) used for correcting
the offset voltages. Both inputs are added together
internally. The capacitors at the auxiliary inputs (C
and CH) hold the corrected values during normal
operation.
The Output Buffer is designed to drive external loads at
the V
OUT
voltage (V
pin. It also produces a single ended output
is an internal reference voltage).
REF
All of these switches are make-before-break in order to
minimize glitch-induced errors. They are driven by two
clock phases (φ
mode and auto-zeroing mode.
and φ2) that select between normal
1
The clock is derived from an internal R-C oscillator
running at a rate of f
output is divided down to the desired rate. It is also
randomized to minimize (spread) undesired clock
tones in the output.
The internal POR ensures the part starts up in a known
good state. It also provides protection against power
supply brown out events.
The Chip Select input places the op amp in a low power
state when it is high. When it goes low, it powers the op
amp at its normal level and starts operation properly.
The Digital Control circuitry takes care of all of the
housekeeping details of the switching operation. It also
takes care of Chip Select and POR events.
MCP6V06/7/8
VIN+
V
IN
–
Main
Output
V
OUT
V
REF
Amp.
Buffer
NC
Null
Amp.
C
H
C
FW
VIN+
V
IN
–
Main
Output
V
OUT
V
REF
Amp.
Buffer
NC
Null
Amp.
C
H
C
FW
4.1.2AUTO-ZEROING ACTION
Figure 4-2 shows the connections between amplifiers
during the Normal Mode of operation (φ
). The hold
1
capacitor (CH) corrects the Null Amplifier’s input offset.
Since the Null Amplifier has very high gain, it
dominates the signal seen by the Main Amplifier. This
greatly reduces the impact of the Main Amplifier’s input
FIGURE 4-2:Normal Mode of Operation (
Figure 4-3 shows the connections between amplifiers
during the Auto-zeroing Mode of operation (φ2). The
signal goes directly through the Main Amplifier, and the
flywheel capacitor (C
tion on the Main Amplifier’s offset.
The Null Amplifier uses its own high open loop gain to
drive the voltage across C
offset voltage is almost zero. Because the principal
input is connected to V
corrects the offset at the current common mode input
voltage (V
) and supply voltage (VDD). This makes
CM
the DC CMRR and PSRR very high also.
) maintains a constant correc-
FW
to the point where its input
H
+, the auto-zeroing action
IN
offset voltage on overall performance. Essentially, the
Null Amplifier and Main Amplifier behave as a regular
op amp with very high gain (AOL) and very low offset
voltage (V
φ
); Equivalent Amplifier Diagram.
1
OS
).
Since these corrections happen every 50 µs, or so, we
also minimize slow errors, including offset drift with
temperature (ΔV
/ΔTA), 1/f noise, and input offset
OS
aging.
FIGURE 4-3:Auto-zeroing Mode of Operation (
4.1.3INTERMODULATION DISTORTION
(IMD)
The MCP6V06/7/8 op amps will show intermodulation
φ
); Equivalent Diagram.
2
frequencies. IMD distortion tones are generated about
all of the square wave clock’s harmonics. See
Figure 2-37 and Figure 2-38.
distortion (IMD), products when an AC signal is
present.
The signal and clock can be decomposed into sine
wave tones (Fourier series components). These tones
interact with the auto-zeroing circuitry’s non-linear
response to produce IMD tones at sum and difference
The input stage of the MCP6V06/7/8 op amps uses two
differential CMOS input stages in parallel. One
operates at low common mode input voltage (V
which is approximately equal to VIN+ and VIN– in normal operation) and the other at high V
CM
topology, the input operates with VCM up to 0.2V past
either supply rail at +25°C (see Figure 2-18). The input
offset voltage (V
) is measured at VCM=VSS–0.2V
OS
and VDD+ 0.2V to ensure proper operation.
The transition between the input stages occurs when
≈ VDD– 0.9V (see Figure 2-7 and Figure 2-8). For
V
CM
the best distortion and gain linearity, with non-inverting
gains, avoid this region of operation.
4.2.1.1Phase Reversal
The input devices are designed to not exhibit phase
inversion when the input pins exceed the supply
voltages. Figure 2-43 shows an input voltage
exceeding both supplies with no phase inversion.
4.2.1.2Input Voltage and Current Limits
The ESD protection on the inputs can be depicted as
shown in Figure 4-4. This structure was chosen to
protect the input transistors, and to minimize input bias
current (I
when they try to go more than one diode drop below
V
SS
above VDD; their breakdown voltage is high enough to
allow normal operation, and low enough to bypass
quick ESD events within the specified limits.
). The input ESD diodes clamp the inputs
B
. They also clamp any voltages that go too far
CM
. With this
pins (V
+ and VIN–) from going too far above VDD, and
IN
dump any currents onto VDD. When implemented as
shown, resistors R1 and R2 also limit the current
through D
and D2.
1
,
FIGURE 4-5:Protecting the Analog
Inputs.
It is also possible to connect the diodes to the left of the
resistor R
the diodes D1 and D2 need to be limited by some other
mechanism. The resistors then serve as in-rush current
limiters; the DC current into the input pins (V
VIN–) should be very small.
A significant amount of current can flow out of the
inputs (through the ESD diodes) when the common
mode voltage (V
Figure 2-17. Applications that are high impedance may
need to limit the usable voltage range.
and R2. In this case, the currents through
1
+ and
IN
) is below ground (VSS); see
CM
FIGURE 4-4:Simplified Analog Input ESD
Structures.
In order to prevent damage and/or improper operation
of these amplifiers, the circuit must limit the currents
(and voltages) at the input pins (see Section 1.1“Absolute Maximum Ratings †”). Figure 4-5 shows
the recommended approach to protecting these inputs.
The internal ESD diodes prevent the input pins (V
and V
resistors R
of the input pins. Diodes D1 and D2 prevent the input
The output voltage range of the MCP6V06/7/8
auto-zeroed op amps is V
V
+ 15 mV (maximum) when RL=20kΩ is
SS
connected to V
/2 and VDD= 5.5V. Refer to
DD
– 15 mV (minimum) and
DD
Figure 2-19 and Figure 2-20 for more information.
These op amps are designed to drive light loads; use
another amplifier to buffer the output from heavy loads.
4.2.3CHIP SELECT (CS)
The single MCP6V08 has a Chip Select (CS) pin.
When CS
corresponding op amp drops to about 1 µA (typical),
and is pulled through the CS
happens, the amplifier is put into a high impedance
state. By pulling CS
CS pin is left floating, the internal pull-down resistor
(about 5 MΩ) will keep the part on. Figure 1-4 shows
the output voltage and supply current response to a CS
+
IN
pulse.
is pulled high, the supply current for the
pin to VSS. When this
low, the amplifier is enabled. If the
MCP6V06/7/8
VOSTA() VOSTC1ΔTTC2ΔT
2
++=
Where:
ΔT=T
A
–25°C
V
OS(TA
)=input offset voltage at T
A
V
OS
=input offset voltage at +25°C
TC
1
=linear temperature coefficient
TC
2
=quadratic temperature
coefficient
R
ISO
C
L
V
OUT
MCP6V0X
10
100
1000
10000
1.E-121.E-111.E-101.E-091.E-081.E-07
C
L
(F)
Recommended R
ISO
(Ω)
1p10p100p1n10n100n
10
100
1k
10k
GN < 2
GN = 5
G
N
= 10
4.3Application Tips
4.3.1INPUT OFFSET VOLTAGE OVER
TEMPERATURE
Table 1-1 gives both the linear and quadratic tempera-
ture coefficients (TC1 and TC2) of input offset voltage.
The input offset voltage, at any temperature in the
specified range, can be calculated as follows:
EQUATION 4-1:
4.3.2DC GAIN PLOTS
Figure 2-9, Figure 2-10 and Figure 2-11 are histograms
of the reciprocals (in units of µV/V) of CMRR, PSRR
and A
input offset voltage (VOS) with a change in common
mode input voltage (V
and output voltage (V
The 1/A
the measurements are dominated by the op amp’s
input noise. The negative values shown represent
noise, not unstable behavior. We validate the op amps’
stability by making multiple measurements of V
instability would manifest itself as a greater unexplained variability in V
, respectively. They represent the change in
OL
), power supply voltage (VDD)
CM
).
OUT
histogram is centered near 0 µV/V because
OL
or as the railing of the output.
OS
OS
4.3.5CAPACITIVE LOADS
Driving large capacitive loads can cause stability
problems for voltage feedback op amps. As the load
capacitance increases, the feedback loop’s phase
margin decreases and the closed-loop bandwidth is
reduced. This produces gain peaking in the frequency
response, with overshoot and ringing in the step
response. These auto-zeroed op amps have a different
output impedance than most op amps, due to their
unique topology.
When driving a capacitive load with these op amps, a
series resistor at the output (R
in Figure 4-6)
ISO
improves the feedback loop’s phase margin (stability)
by making the output load resistive at higher frequencies. The bandwidth will be generally lower than the
bandwidth with no capacitive load.
FIGURE 4-6:Output Resistor, R
ISO
,
Stabilizes Capacitive Loads.
Figure 4-7 gives recommended R
different capacitive loads and is independent of the
gain.
;
values for
ISO
4.3.3SOURCE RESISTANCES
The input bias currents have two significant
components; switching glitches that dominate at room
temperature and below, and input ESD diode leakage
currents that dominate at +85°C and above.
Make the resistances seen by the inputs small and
equal. This minimizes the output offset caused by the
input bias currents.
The inputs should see a resistance on the order of 10Ω
to 1 kΩ at high frequencies (i.e., above 1 MHz). This
helps minimize the impact of switching glitches, which
are very fast, on overall performance. In some cases, it
may be necessary to add resistors in series with the
inputs to achieve this improvement in performance.
4.3.4SOURCE CAPACITANCE
The capacitances seen by the two inputs should be
small and matched. The internal switches connected to
the inputs dump charges on these capacitors; an offset
can be created if the capacitances do not match.
After selecting R
resulting frequency response peaking and step
response overshoot. Modify R
response is reasonable. Bench evaluation and
simulations with the MCP6V06 SPICE macro model
(good for all of the MCP6V06/7/8 op amps) are helpful.
for your circuit, double check the
ISO
's value until the
ISO
MCP6V06/7/8
MCP6V0X
V
S_ANA
143Ω143Ω
100 µF
100 µF
0.1 µF
1/4W1/10W
to other analog parts
4.3.6REDUCING UNDESIRED NOISE
AND SIGNALS
Reduce undesired noise and signals with:
• Low bandwidth signal filters:
- Minimizes random analog noise
- Reduces interfering signals
• Good PCB layout techniques:
- Minimizes crosstalk
- Minimizes parasitic capacitances and inductances that interact with fast switching edges
• Good power supply design:
- Isolation from other parts
- Filtering of interference on supply line(s)
4.3.7SUPPLY BYPASSING AND
FILTERING
With this family of operational amplifiers, the power
supply pin (V
bypass capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm
of the pin for good high-frequency performance.
These parts also need a bulk capacitor (i.e., 1 µF or
larger) within 100 mm to provide large, slow currents.
This bulk capacitor can be shared with other low noise,
analog parts.
Additional filtering of high frequency power supply
noise (e.g., switched mode power supplies) can be
achieved using resistors. The resistors need to be
small enough to prevent a large drop in V
amp, which would cause a reduced output range and
possible load-induced power supply noise. The resistors also need to be large enough to dissipate little
power when V
cuit in Figure 4-8 gives good rejection out to 1 MHz for
switched mode power supplies. Smaller resistors and
capacitors are a better choice for designs where the
power supply is reasonably quiet.
for single supply) should have a local
DD
for the op
DD
is turned on and off quickly. The cir-
DD
4.3.8PCB DESIGN FOR DC PRECISION
In order to achieve DC precision on the order of ±1 µV,
many physical errors need to be minimized. The design
of the Printed Circuit Board (PCB), the wiring, and the
thermal environment has a strong impact on the
precision achieved. A poor PCB design can easily be
more than 100 times worse than the MCP6V06/7/8 op
amps minimum and maximum specifications.
4.3.8.1Thermo-junctions
Any time two dissimilar metals are joined together, a
temperature dependent voltage appears across the
junction (the Seebeck or thermo-junction effect). This
effect is used in thermocouples to measure temperature. The following are examples of thermo-junctions
on a PCB:
• Components (resistors, op amps, …) soldered to
a copper pad
• Wires mechanically attached to the PCB
• Jumpers
• Solder joints
•PCB vias
Typical thermo-junctions have temperature to voltage
conversion coefficients of 10 to 100 µV/°C (sometimes
higher).
There are three basic approaches to minimizing
thermo-junction effects:
• Minimize thermal gradients
• Cancel thermo-junction voltages
• Minimize difference in thermal potential between
metals
4.3.8.2Non-inverting and Inverting Amplifier
Layout for Thermo-junctions
Figure 4-9 shows the recommended non-inverting and
inverting gain amplifier circuits on one schematic.
Usually, to minimize the input bias current related off-
is chosen to be R2||R3.
set, R
1
The guard traces (with ground vias at the ends) help
minimize the thermal gradients. The resistor layout
cancels the resistor thermal voltages, assuming the
temperature gradient is constant near the resistors:
EQUATION 4-2:
4.3.8.3Difference Amplifier Layout for
Thermo-junctions
Figure 4-10 shows the recommended difference ampli-
fier circuit. Usually, we choose R
1=R2
and R3=R4.
The guard traces (with ground vias at the ends) help
minimize the thermal gradients. The resistor layout
cancels the resistor thermal voltages, assuming the
temperature gradient is constant near the resistors:
EQUATION 4-3:
FIGURE 4-9:PCB Layout and Schematic
for Single Non-inverting and Inverting Amplifiers.
Note:Changing the orientation of the resistors
will usually cause a significant decrease in
the cancellation of the thermal voltages.
FIGURE 4-10:PCB Layout and Schematic
for Single Difference Amplifier.
Note:Changing the orientation of the resistors
will usually cause a significant decrease in
the cancellation of the thermal voltages.
MCP6V06/7/8
(VOA–VOB) ≈ (VIA–VIB)G
DM
(VOA+VOB)/2 ≈ (VIA+VIB)/2
Where:
Thermal voltages are approximately equal
G
DM
=1+R3/R2, differential mode gain
G
CM
=1, common mode gain
VOSis neglected
V
IB
V
OB
R
1
U
1
½MCP6V07
U1
V
IB
V
IA
R1
R2
R3
R1
R2
R3
V
IA
R
3
V
OA
R
1
R
2
U
1
½MCP6V07
R
3
R
2
V
OAVOB
R
1B
R
1A
R
2B
R
2A
R
1B
R
1A
R
2B
R
2A
4.3.8.4Dual Non-inverting Amplifier Layout
for Thermo-junctions
The dual op amp amplifiers shown in Figure 4-14 and
Figure 4-15 produce a non-inverting difference gain
greater than 1, and a common mode gain of 1 .They
can use the layout shown in Figure 4-11. The gain set-
ting resistors (R
) between the two sides are not com-
2
bined so that the thermal voltages can be canceled.
The guard traces (with ground vias at the ends) help
minimize the thermal gradients. The resistor layout
cancels the resistor thermal voltages, assuming the
temperature gradient is constant near the resistors:
EQUATION 4-4:
4.3.8.5Other PCB Thermal Design Tips
In cases where an individual resistor needs to have its
thermo-junction voltage cancelled, it can be split into
two equal resistors as shown in Figure 4-12. To keep
the thermal gradients near the resistors as small as
possible, the layouts are symmetrical with a ring of
metal around the outside. Make R
R
2A=R2B
=2R2.
1A=R1B=R1
/2 and
FIGURE 4-12:PCB Layout for Individual
Resistors.
Note:Changing the orientation of the resistors
will usually cause a significant decrease in
the cancellation of the thermal voltages.
FIGURE 4-11:PCB Layout and Schematic
for Dual Non-inverting Amplifier.
will usually cause a significant decrease in
the cancellation of the thermal voltages.
Minimize temperature gradients at critical components
(resistors, op amps, heat sources, etc.):
• Minimize exposure to gradients
- Small components
- Tight spacing
- Shield from air currents
• Align with constant temperature (contour) lines
- Place on PCB center line
• Minimize magnitude of gradients
- Select parts with lower power dissipation
- Use same metal junctions on thermo-junctions that need to match
- Use metal junctions with low temperature to
voltage coefficients
- Large distance from heat sources
- Ground plane underneath (large area)
- FR4 gaps (no copper for thermal insulation)
- Series resistors inserted into traces (adds
thermal and electrical resistance)
- Use heat sinks
Make the temperature gradient point in one direction:
• Add guard traces
- Constant temperature curves follow the
traces
- Connect to ground plane
• Shape any FR4 gaps
- Constant temperature curves follow the
edges
MCP6V06/7/8
V
DD
RR
RR
100R
0.01C
MCP6V06
ADC
V
DD
0.2R
0.2R
3kΩ
20 kΩ
1µF
200Ω
20 kΩ
1µF
ADC
V
DD
½ MCP6V07
½ MCP6V07
200 Ω
200 Ω
3kΩ
3kΩ
1µF
RR
RR
V
DD
10 nF
10 nF
200Ω
4.3.8.6Crosstalk
DC crosstalk causes offsets that appear as a larger
input offset voltage. Common causes include:
• Common mode noise (remote sensors)
• Ground loops (current return paths)
• Power supply coupling
Interference from the mains (usually 50 Hz or 60 Hz),
and other AC sources, can also affect the DC performance. Non-linear distortion can convert these signals
to multiple tones, included a DC shift in voltage. When
the signal is sampled by an ADC, these AC signals can
also be aliased to DC, causing an apparent shift in
offset.
To reduce interference:
- Keep traces and wires as short as possible
- Use shielding (e.g., encapsulant)
- Use ground plane (at least a star ground)
- Place the input signal source near to the DUT
- Use good PCB layout techniques
- Use a separate power supply filter (bypass
capacitors) for these auto-zeroed op amps
4.3.8.7Miscellaneous Effects
Keep the resistances seen by the input pins as small
and as near to equal as possible to minimize bias current related offsets.
Make the (trace) capacitances seen by the input pins
small and equal. This is helpful in minimizing switching
glitch-induced offset voltages.
Bending a coax cable with a radius that is too small
causes a small voltage drop to appear on the center or
(the tribo-electric effect). Make sure the bending radius
is large enough to keep the conductors and insulation
in full contact.
Mechanical stresses can make some capacitor types
(such as ceramic) to output small voltages. Use more
appropriate capacitor types in the signal path and
minimize mechanical stresses and vibration.
Humidity can cause electro-chemical potential voltages
to appear in a circuit. Proper PCB cleaning helps, as
does the use of encapsulants.
4.4Typical Applications
4.4.1WHEATSTONE BRIDGE
Many sensors are configured as Wheatstone bridges.
Strain gauges and pressure sensors are two common
examples. These signals can be small and the
common mode noise large. Amplifier designs with high
differential gain are desirable.
Figure 4-13 shows how to interface to a Wheatstone
bridge with a minimum of components. Because the
circuit is not symmetric, the ADC input is single ended,
and there is a minimum of filtering, the CMRR is good
enough for moderate common mode noise.
FIGURE 4-13:Simple Design.
Figure 4-14 shows a higher performance circuit for
Wheatstone bridges. This circuit is symmetric and has
high CMRR. Using a differential input to the ADC helps
with the CMRR.
The ratiometric circuit in Figure 4-15 conditions a three
wire RTD. It corrects for the sensor’s wiring resistance
by subtracting the voltage across the middle R
top R1 does not change the output voltage; it balances
the op amp inputs. Failure (open) of the RTD is
detected by an out-of-range voltage.
. The
W
gain is is set so that V
is 10 mV/°C. V3 represents
4/THJ
the output of a temperature sensor, which produces a
voltage proportional to the temperature (in °C) at the
cold junction (T
), and with a 0.50V offset. V2 is set so
CJ
that V4 is 0.50V when THJ–TCJ is 0°C.
EQUATION 4-5:
FIGURE 4-15:RTD Sensor.
The voltages at the input of the ADC can be calculated
with the following:
4.4.3THERMOCOUPLE SENSOR
Figure 4-16 shows a simplified diagram of an amplifier
and temperature sensor used in a thermocouple
application. The type K thermocouple senses the
temperature at the hot junction (T
voltage at V
Figure 4-17 shows a more complete implementation of
this circuit. The dashed red arrow indicates a thermally
conductive connection between the thermocouple and
the MCP9700A; it needs to be very short and have low
thermal resistance.
FIGURE 4-17:Thermocouple Sensor.
The MCP9700A senses the temperature at its physical
location. It needs to be at the same temperature as the
cold junction (T
), and produces V3 (Figure 4-14).
CJ
MCP6V06/7/8
MCP6V06
C
2
R
2
R
1
R
3
MCP6XXX
VDD/2
3kΩ
V
IN
V
OUT
R
2
MCP6V06
V
IN
R
3
R
2
VDD/2
MCP6541
V
OUT
R
5
R
4
R
1
1kΩ
The MCP1541 produces a 4.10V output, assuming
VDD is at 5.0V. This voltage, tied to a resistor ladder of
4.100R and 1.3224R, would produce a Thevenin equivalent of 1.00V and 250R. The 1.3224R resistor is combined in parallel with the top right R resistor (in
Figure 4-16), producing the 0.5696R resistor.
should be converted to digital, then corrected for the
V
4
thermocouple’s non-linearity. The ADC can use the
MCP1541 as its voltage reference. Alternately, an
absolute reference inside a PIC can be used instead of
the MCP1541.
4.4.4OFFSET VOLTAGE CORRECTION
Figure 4-18 shows a MCP6V06 correcting the input
offset voltage of another op amp. R2 and C2 integrate
the offset error seen at the other op amp’s input; the
integration needs to be slow enough to be stable (with
the feedback provided by R
and R3).
1
4.4.5PRECISION COMPARATOR
Use high gain before a comparator to improve the
latter’s performance. Do not use MCP6V06/7/8 as a
comparator by itself; the V
Microchip provides the basic design aids needed for
the MCP6V06/7/8 family of op amps.
5.1SPICE Macro Model
The latest SPICE macro model for the MCP6V06/7/8
op amps is available on the Microchip web site at
www.microchip.com. This model is intended to be an
initial design tool that works well in the op amp’s linear
region of operation over the temperature range. See
the model file for information on its capabilities.
Bench testing is a very important part of any design and
cannot be replaced with simulations. Also, simulation
results using this macro model need to be validated by
comparing them to the data sheet specifications and
characteristic curves.
5.2FilterLab® Software
Microchip’s FilterLab® software is an innovative
software tool that simplifies analog active filter (using
op amps) design. Available at no cost from the Microchip web site at www.microchip.com/filterlab, the Filter-Lab design tool provides full schematic diagrams of
the filter circuit with component values. It also outputs
the filter circuit in SPICE format, which can be used
with the macro model to simulate actual filter performance.
5.3Mindi™ Circuit Designer &
Simulator
Microchip’s Mindi™ Circuit Designer & Simulator aids
in the design of various circuits useful for active filter,
amplifier and power management applications. It is a
free online circuit designer & simulator available from
the Microchip web site at www.microchip.com/mindi.
This interactive circuit designer & simulator enables
designers to quickly generate circuit diagrams, and
simulate circuits. Circuits developed using the Mindi
Circuit Designer & Simulator can be downloaded to a
personal computer or workstation.
5.4Microchip Advanced Part Selector
(MAPS)
5.5Analog Demonstration and
Evaluation Boards
Microchip offers a broad spectrum of Analog Demonstration and Evaluation Boards that are designed to
help customers achieve faster time to market. For a
complete listing of these boards and their corresponding user’s guides and technical information, visit the
Microchip web site at www.microchip.com/analog
tools.
Some boards that are especially useful are:
• MCP6V01 Thermocouple Auto-Zeroed Reference
Design
• MCP6XXX Amplifier Evaluation Board 1
• MCP6XXX Amplifier Evaluation Board 2
• MCP6XXX Amplifier Evaluation Board 3
• MCP6XXX Amplifier Evaluation Board 4
• Active Filter Demo Board Kit
• P/N SOIC8EV: 8-Pin SOIC/MSOP/TSSOP/DIP
Evaluation Board
• P/N SOIC14EV: 14-Pin SOIC/TSSOP/DIP
Evaluation Board
5.6Application Notes
The following Microchip Application Notes are
available on the Microchip web site at www.microchip.
com/appnotes and are recommended as supplemental
reference resources.
ADN003: “Select the Right Operational Amplifier for
your Filtering Circuits”, DS21821
AN722: “Operational Amplifier Topologies and DC
Specifications”, DS00722
AN723: “Operational Amplifier AC Specifications and
Applications”, DS00723
AN884:“Driving Capacitive Loads With Op Amps”,
DS00884
AN990: “Analog Sensor Conditioning Circuits – An
Overview”, DS00990
These application notes and others are listed in the
design guide:
“Signal Chain Design Guide”, DS21825
MAPS is a software tool that helps efficiently identify
Microchip devices that fit a particular design requirement. Available at no cost from the Microchip website
at www.microchip.com/maps, the MAPS is an overall
selection tool for Microchip’s product portfolio that
includes Analog, Memory, MCUs and DSCs. Using this
tool, a customer can define a filter to sort features for a
parametric search of devices and export side-by-side
technical comparison reports. Helpful links are also
provided for Data sheets, Purchase and Sampling of
Microchip parts.
YYear code (last digit of calendar year)
YYYear code (last 2 digits of calendar year)
WWWeek code (week of January 1 is week ‘01’)
NNNAlphanumeric traceability code
Pb-free JEDEC designator for Matte Tin (Sn)
*This package is Pb-free. The Pb-free JEDEC designator ()
can be found on the outer packaging for this package.
Note:In the event the full Microchip part number cannot be marked on one line, it will
be carried over to the next line, thus limiting the number of available
characters for customer-specific information.
We use production screens to ensure the quality of our
outgoing products. These screens are set at wider lim-
its to eliminate any fliers; see Ta bl e B - 1 .
Input offset voltage related specifications in the DC
spec table (Table 1-1) are based on bench measure-
ments (see Section 2.1 “DC Input Precision”). These
measurements are much more accurate because:
• More compact circuit
• Soldered parts on the PCB
• More time spent averaging (reduces noise)
• Better temperature control
- Reduced temperature gradients
- Greater accuracy
TABLE B-1:OFFSET RELATED TEST SCREENS
Electrical Characteristics: Unless otherwise indicated, TA = 25°C, VDD = +1.8V to +5.5V, VSS = GND, VCM = VDD/3,
V
OUT=VDD
Input Offset
Input Offset VoltageV
Input Offset Voltage Drift with Temperature
(linear Temp. Co.)
Power Supply RejectionPSRR115—dB(Note 1)
Common Mode
Common Mode RejectionCMRR106—dBV
Open-Loop Gain
DC Open-Loop Gain (large signal)A
Note 1:Due to thermal junctions and other errors in the production environment, these specifications are only screened in
/2, VL=VDD/2, RL = 20 kΩ to VL, and CS = GND (refer to Figure 1-5 and Figure 1-6).
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
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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.
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WARRANTIES OF ANY KIND WHETHER EXPRESS OR
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The Microchip name and logo, the Microchip logo, Accuron,
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