Dual-Channel, Platinum RTD-to-Voltage
Signal Conditioner
Pin Description
PIN
NAME
FUNCTION
1
VCC
Power-Supply Input. Bypass to GND with a 0.1µF capacitor as close to VCC as possible.
2
RS2-
Sense Resistor 2 Negative Input
3
RS2+
Sense Resistor 2 Positive Input
4
RS1+
Sense Resistor 1 Positive Input
5
RS1-
Sense Resistor 1 Negative Input
6
GND
Ground
7
DG1
Diagnostic Output Signal 1. DG1 asserts low upon fault detection.
8
OUT1
Output Analog Voltage 1. OUT1 is high impedance upon DG1 assertion.
9
OUT2
Output Analog Voltage 2. OUT2 is high impedance upon DG2 assertion.
10
DG2
Diagnostic Output Signal 2. DG2 asserts low upon fault detection.
—
EP
Exposed Pad. Connect to GND.
Functional Block Diagram
VCC
RS1+
VCC
RSRC
ESD
CLAMP
MAX6603
AMP
RS1-
ESD
CLAMP
VCC
IEXC
HI-V
DETECT
FAULT
DETECT
OUT1
DG1
RSRC
RS2+
ESD
CLAMP
AMP
RS2-
ESD
CLAMP
IEXC
HI-V
DETECT
FAULT
DETECT
OUT2
DG2
GND
Detailed Description
The MAX6603 converts a Deutsche Institute for Normung
(DIN) standard 200Ω Pt RTD to a high-level analog volt-
age without the need for external trims or precise dis-
crete components. The Pt RTD resistance conveys
temperature information approximated by the Callendar-
Van Dusen equation and is represented in Figure 1:
R(T) = RO[1 + AT + BT2+ CT3]
where: R(T) = Resistance of Pt RTD at temperature (T)
R0 = Base resistance in ohms at 0°C
T = Temperature in °C
A = 3.9083 E-3 °C-1 (alpha coefficient 1)
B = -5.7750 E-7 °C-2 (alpha coefficient 2)
C = 0 (approximation for temperatures > 0°C)
(Alpha coefficients can vary depending on
standards.)
The MAX6603 applies a constant excitation current of
1mA (typ) through the Pt RTD, generating a voltage
drop that is amplified and results in a high-level output
voltage. The excitation current (IEXC) typically varies
ratiometrically by 0.2mA/V (typ) with respect to VCC,
and therefore, the amplified signal is ratiometric to the
power supply. The voltage amplification from input to
output is 5 (typ). The output voltage is applied to a
ratiometric ADC to produce a digital value independent
of supply voltage. For ADCs that use VCC as their refer-
ence voltage, sudden changes in the supply voltage do
not affect the microcontroller’s reading of the tempera-
ture. Ratiometricity simplifies the connection to most
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