SNIS245B September   2025  – July 2026 ISOTMP35R-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Insulation Specification
    6. 6.6  Power Ratings
    7. 6.7  Safety-Related Certifications
    8. 6.8  Safety Limiting Values
    9. 6.9  Electrical Characteristics
    10. 6.10 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Functional Description
      1. 7.3.1 Integrated Isolation Barrier
      2. 7.3.2 Output Stage and Signal Behavior
        1. 7.3.2.1 Transfer Function
        2. 7.3.2.2 Driving Capacitive Loads
        3. 7.3.2.3 Common Mode Transient Immunity (CMTI)
      3. 7.3.3 Thermal Response
        1. 7.3.3.1 Stirred Liquid Thermal Response
        2. 7.3.3.2 Directional Thermal Response
          1. 7.3.3.2.1 Comparison to NTC Thermistors
        3. 7.3.3.3 Still Air Thermal Response
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Improving Accuracy Using Piecewise Linear Approximation
      2. 8.1.2 Output Buffering and Signal Integrity Considerations
      3. 8.1.3 ADC Interface Considerations
      4. 8.1.4 Power Supply Recommendations
      5. 8.1.5 EMI Mitigation and Filtering
        1. 8.1.5.1 Filtering Techniques
        2. 8.1.5.2 Design Guidelines for EMI Filtering
      6. 8.1.6 Insulation Lifetime
    2. 8.2 Layout
      1. 8.2.1 Layout Guidelines
      2. 8.2.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Mechanical Data
    2. 11.2 Package Option Addendum
    3. 11.3 Tape and Reel Information
7.3.3.2.1 Comparison to NTC Thermistors

Comparison to NTC thermistors highlights the benefit of direct thermal coupling enabled by the ISOTMP35R-Q1. In this test, heat is applied through a high-voltage copper plane connected to the TSENSE pins, while the low-voltage side remains at 25°C. A temperature step of 100°C (25°C to 125°C) is applied at the heat source. This condition represents applications where the temperature of interest is localized at the heat source rather than uniformly distributed across the package.

Figure 7-9 shows the test configurations for the ISOTMP35R-Q1 and discrete NTC implementations. The ISOTMP35R-Q1 is thermally coupled directly to the heat source through the TSENSE pins. In contrast, the NTC thermistors are positioned approximately 8mm away and rely on heat transfer through PCB material and, in one configuration, a thermal conductive epoxy.

ISOTMP35R-Q1 Test Setup: ISOTMP35R-Q1 vs NTCFigure 7-9 Test Setup: ISOTMP35R-Q1 vs NTC

Figure 7-10 shows the measured thermal response of the ISOTMP35R-Q1 compared to two NTC configurations: with and without thermal epoxy.

ISOTMP35R-Q1 Thermal Response ComparisonFigure 7-10 Thermal Response Comparison

As summarized in Table 7-2, the ISOTMP35R-Q1 reaches the final temperature significantly faster and remains closer to the 125°C reference during the transient response. This behavior results from the direct thermal coupling through the TSENSE pins, which minimizes thermal resistance between the heat source and the sensing element.

Table 7-2 Response Time and Final Temperature Comparison
ParameterISOTMP35R-Q1NTC (with Epoxy)NTC (without Epoxy)
Thermal Coupling PathDirect
(through TSENSE pins)		Remote
(FR-4 PCB with thermal epoxy)		Remote
(FR-4 PCB conductive path only)
Coupling Material ConductivityCopper: 400W/mKEpoxy: 3.7W/mKFR-4: 0.2W/mK
Distance from Heat SourceDirectly coupled8mm8mm
Response Time (τ63%)4.7s75.0s90.5s
Response Time (τ86%)24.6s143.4s173.6s
Final Temperature121.5°C92.5°C90.5°C
Note:

Thermal conductivity values shown are representative bulk values of the primary materials in the thermal coupling path and are provided for relative comparison only. Effective thermal response depends on the complete thermal path, including geometry, interface thickness, contact area, and PCB construction.

In contrast, NTC implementations introduce additional thermal resistance and delay due to physical separation from the heat source and the presence of intermediate materials. The use of thermal epoxy improves conduction compared to a bare NTC, but still results in slower response and increased deviation from the reference temperature.

Additional details on test methodology, thermal modeling, and system-level considerations are provided in application note Improving Thermal Response Time and Accuracy in High- Voltage Applications.