Microchip Technology MCP6V01RD-TCPL Data Sheet
MCP6V01/2/3
DS22058C-page 30
© 2008 Microchip Technology Inc.
4.4.3
THERMOCOUPLE SENSOR
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
application. The type K thermocouple senses the
temperature at the hot junction (T
HJ
), and produces a
voltage at V
1
proportional to T
HJ
(in °C). The amplifier’s
gain is is set so that V
4
/T
HJ
is 10 mV/°C. V
3
represents
the output of a temperature sensor, which produces a
voltage proportional to the temperature (in °C) at the
cold junction (T
voltage proportional to the temperature (in °C) at the
cold junction (T
CJ
), and with a 0.50V offset. V
2
is set so
that V
4
is 0.50V when T
HJ
– T
CJ
is 0°C.
EQUATION 4-5:
FIGURE 4-18:
Thermocouple Sensor;
Simplified Circuit.
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.
conductive connection between the thermocouple and
the MCP9700A; it needs to be very short and have low
thermal resistance.
FIGURE 4-19:
Thermocouple Sensor.
The MCP9700A senses the temperature at its physical
location. It needs to be at the same temperature as the
cold junction (T
location. It needs to be at the same temperature as the
cold junction (T
CJ
), and produces V
3
(
The MCP1541 produces a 4.10V output, assuming
V
V
DD
is at 5.0V. This voltage, tied to a resistor ladder of
4.100(R
TH
) and 1.3224(R
TH
), would produce a Theve-
nin equivalent of 1.00V and 250(R
TH
). The
1.3224(R
TH
) resistor is combined in parallel with the
top right R
TH
resistor (in
), producing the
0.5696(R
TH
) resistor.
V
4
should be converted to digital, then corrected for the
thermocouple’s non-linearity. The ADC can use the
MCP1541 as its voltage reference. Alternately, an
absolute reference inside a PICmicro
MCP1541 as its voltage reference. Alternately, an
absolute reference inside a PICmicro
®
can be used
instead of the MCP1541.
4.4.4
OFFSET VOLTAGE CORRECTION
shows a MCP6V01 correcting the input
offset voltage of another op amp. R
2
and C
2
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
integration needs to be slow enough to be stable (with
the feedback provided by R
1
and R
3
).
FIGURE 4-20:
Offset Correction.
4.4.5
PRECISION COMPARATOR
Use high gain before a comparator to improve the
latter’s performance. Do not use MCP6V01/2/3 as a
comparator by itself; the V
latter’s performance. Do not use MCP6V01/2/3 as a
comparator by itself; the V
OS
correction circuitry does
not operate properly without a feedback loop.
FIGURE 4-21:
Precision Comparator.
V
1
≈ T
HJ
(40 µV/°C)
V
2
= (1.00V)
V
3
= T
CJ
(10 mV/°C) + (0.50V)
V
4
= 250V
1
+ (V
2
– V
3
)
≈ (10 mV/°C) (T
HJ
– T
CJ
) + (0.50V)
(R
TH
)/250
(R
TH
)
(R
TH
)/250
C
(R
TH
)
C
V
4
MCP6V01
Type K
40 µV/°C
(R
TH
)
(R
TH
)
V
1
V
3
(hot junction
(cold junction
V
2
Thermocouple
at T
HJ
)
at T
CJ
)
R
TH
= Thevenin Equivalent Resistance
(R
TH
)/250
0.5696(R
TH
)
(R
TH
)/250
C
(R
TH
)
C
V
4
MCP6V01
Type K
(R
TH
)
4.100(R
TH
)
V
1
MCP9700A
V
DD
MCP1541
V
DD
3 k
Ω
R
TH
= Thevenin Equivalent Resistance (e.g.: 10 k
Ω)
MCP6V01
C
2
R
2
R
1
R
3
MCP6XXX
V
DD
/2
3 k
Ω
V
IN
V
OUT
R
2
MCP6V01
V
IN
R
3
R
2
V
DD
/2
MCP6541
V
OUT
R
5
R
4
R
1
1 k
Ω