SBOU312 august   2023 ISOTMP35 , ISOTMP35-Q1

 

  1.   1
  2.   Description
  3.   Get Started
  4.   Features
  5.   Applications
  6.   6
  7. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Specification
    4. 1.4 Device Information
    5. 1.5 General Texas Instruments High Voltage Evaluation (TI HV EVM) User Safety Guidelines
  8. 2Hardware
    1. 2.1 Overview
    2. 2.2 High Voltage Connection Setup Guide
      1. 2.2.1 Detaching the Sensor
      2. 2.2.2 Attaching Sensor Section to High Voltage Heat Source
    3. 2.3 Perforations
    4. 2.4 Status LEDs & Subregulator
    5. 2.5 Programming Header
    6. 2.6 Pushbutton Switch
    7. 2.7 RC Filter
  9. 3Software
    1. 3.1 Software Download
      1. 3.1.1 Online Software
      2. 3.1.2 Offline Software
    2. 3.2 Home Tab
    3. 3.3 Data Capture Tab
    4. 3.4 Collateral Tab
  10. 4Hardware Design Files
    1. 4.1 ISOTMP35BEVM Schematic
    2. 4.2 PCB Layout
    3. 4.3 Bill of Materials
  11. 5Additional Information
    1.     Trademarks

2.7 RC Filter

On the sensor breakout board, R15 and C20 can be used for an optional RC circuit to filter the voltage output of the ISOTMP35. R15 is already installed on the board, but is a 0 Ohm jumper so acts as a short. C20 is not installed by default. The user can desolder R15, solder on a different resistor in the place of R15, and solder on a capacitor for C20 to create an RC filter.

The user must be aware to not use a capacitor value greater than 885 pF for C20. The ISOTMP35 has a maximum capacitive load of 1000 pF, however C17 on the controller portion of the EVM is a 100 pF cap that is loaded onto the output voltage line. C17 prevents the voltage from dropping on the microcontroller ADC input, so C17 must not be removed. The ADC pin of the MSP430F5528 has 15 pF of capacitive loading as well.

A typical value that helps reduce noise in most cases and minimize ADC sampling error is 680 pF. Adding any resistor in place of R15 increases the output settling time, so the user must not exceed 100K Ohms if adding a resistor. An output impedance 10K Ohms is enough to avoid instability on the ISOTMP35 output. A resistor between 10K Ohms to 100K Ohms is acceptable.

In Table 3-2, three resistor and capacitor values for an RC circuit on the ISOTMP35 analog output pin are provided, and the settling time and cutoff frequencies are calculated from that to help the user choose the right resistor and capacitor combination for their application.

  • 115 pF is shown because this is the capacitance already loading the ISOTMP35 analog output (100 pF from C17, 15 pF from ADC pin of microcontroller) if the user does not add any capacitor to C20.
  • 795 pF is shown because this takes the 115 pF already loaded and adds an additional 680 pF load which is recommended above.
  • 1000 pF is shown because this is the maximum capacitive load that can be put onto the ISOTMP35 analog output.
Table 2-2 ISOTMP35 Settling Time & Cutoff Frequencies With Different RC Combinations
Settling Time (us) & Cutoff Frequency (KHz) Settling Time (5*RC Time Constant) Cutoff Frequency (fC = 1/(2πRC))
115 pF 795 pF 1000 pF 115 pF 795 pF 1000 pF
1K Ohms 0.575 us 3.975 us 5 us 1384 KHz 200.3 KHz 159.2 KHz
10K Ohms 5.75 us 39.75 us 50 us 138.4 KHz 20.03 KHz 15.92 KHz
100K Ohms 57.5 us 397.5 us 500 us 13.84 KHz 2.003 KHz 1.592 KHz