SLAA914B September 2019 – March 2020
Design Goals
Temperature | Output voltage | Supply | ||||
---|---|---|---|---|---|---|
TMin | TMax | VoutMin | VoutMax | Vdd | Vee | Vref |
0℃ | 50℃ | 0.15 V | 3.15 V | 3.3 V | 0 V | 1.646 V |
Design Description
Some MSP430™ microcontrollers (MCUs) contain configurable integrated signal chain elements such as op-amps, DACs, and programmable gain stages. These elements make up a peripheral called the Smart Analog Combo (SAC). For information on the different types of SACs and how to leverage their configurable analog signal chain capabilities, visit MSP430 MCUs Smart Analog Combo Training. To get started with your design, download the Temperature Sensing PTC Circuit Design Files.
This temperature sensing circuit uses a resistor in series with a positive-temperature-coefficient (PTC) thermistor to form a voltage divider, which produces an output voltage that is linear over temperature. The circuit uses the MSP430FR2311 SAC_L1 op-amp in a noninverting amplifier configuration with inverting reference to offset and amplify the signal, which helps to use the full ADC resolution and increase measurement accuracy. (Note: The MSP430FR2355 features four SAC_L3 peripherals which each contain a built-in DAC and PGA, providing a single-chip solution for generating Vref and measuring the thermistor circuit.) The output of the integrated SAC op-amp can be sampled directly by the on-board ADC or monitored by the on-board comparator for further processing inside the MCU.
Design Notes
Design Steps
Design Simulations
DC Transfer Results
AC Simulation Results
Target Applications
References
Design Featured Op Amp
MSP430FRxx Smart Analog Combo | ||
---|---|---|
MSP430FR2311 SAC_L1 | MSP430FR2355 SAC_L3 | |
Vcc | 2.0 V to 3.6 V | |
VCM | -0.1 V to VCC + 0.1 V | |
Vout | Rail-to-rail | |
Vos | ±5 mV | |
AOL | 100 dB | |
Iq | 350 µA (high-speed mode) | |
120 µA (low-power mode) | ||
Ib | 50 pA | |
UGBW | 4 MHz (high-speed mode) | 2.8 MHz (high-speed mode) |
1.4 MHz (low-power mode) | 1 MHz (low-power mode) | |
SR | 3 V/µs (high-speed mode) | |
1 V/µs (low-power mode) | ||
Number of channels | 1 | 4 |
http://www.ti.com/product/MSP430FR2311 | ||
http://www.ti.com/product/MSP430FR2355 |
Design Alternate Op Amp
MSP430FR2311 Transimpedance Amplifier | |
---|---|
Vcc | 2.0 V to 3.6 V |
VCM | -0.1 V to VCC/2 V |
Vout | Rail-to-rail |
Vos | ±5 mV |
AOL | 100 dB |
Iq | 350 µA (high-speed mode) |
120 µA (low-power mode) | |
Ib | 5 pA (TSSOP-16 with OA-dedicated pin input) |
50 pA (TSSOP-20 and VQFN-16) | |
UGBW | 5 MHz (high-speed mode) |
1.8 MHz (low-power mode) | |
SR | 4 V/µs (high-speed mode) |
1 V/µs (low-power mode) | |
Number of channels | 1 |
http://www.ti.com/product/MSP430FR2311 |
Design Featured Thermistor
TMP61 | |
---|---|
VCC | Up to 5.5 V |
R25 | 10 kΩ |
RTOL | 1% |
ISNS | 400 µA |
Operating temperature range | -40°C to 125°C |
http://www.ti.com/product/TMP61 |
Related MSP430 Circuits