ISOTMP35RDFPR datasheet(20/44 Pages) TI2

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Table 7-2. Response Time and Final Temperature Comparison

Parameter

ISOTMP35R

NTC (with Epoxy)

NTC (without Epoxy)

Thermal Coupling Path

Direct

(through TSENSE pins)

Remote

(FR-4 PCB with thermal epoxy)

Remote

(FR-4 PCB conductive path only)

Coupling Material Conductivity

Copper: 400W/mK

Epoxy: 3.7W/mK

FR-4: 0.2W/mK

Distance from Heat Source

Directly coupled

8mm

Response Time (τ63%)

4.7s

75.0s

90.5s

Response Time (τ86%)

24.6s

143.4s

173.6s

Final Temperature

121.5°C

92.5°C

90.5°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.

7.3.3.3 Still Air Thermal Response

Still air thermal response represents a worst-case condition where heat transfer occurs primarily through natural

convection. In this environment, the rate of heat transfer is significantly lower than in directional or liquid-based

conditions, resulting in slower response times. This condition highlights the importance of proper thermal

coupling between the TSENSE pins and the heat source. Figure 7-11 shows the corresponding still-air response

behavior.

Time (s)

-100

100

300

500

700

900

100

125

T63%  123.0s

T86%  265.0s

VOUT

Figure 7-11. Thermal Response (Still Air)

7.4 Device Functional Modes

The singular functional mode of the ISOTMP35R is an analog output directly proportional to temperature.

ISOTMP35R

SNIS244A – SEPTEMBER 2025 – REVISED MAY 2026

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