7.3.3.2 Directional Thermal Response

Directional thermal response represents the most application-relevant condition for the ISOTMP35R device. In

this test, heat is applied primarily through the TSENSE pins while the remaining device pins are exposed to

ambient temperature. This configuration reflects real-world use cases where the device is thermally coupled to

a localized high-voltage heat source, such as a power transistor or copper plane, with the rest of the package

influenced by ambient conditions.

Figure 7-7 illustrates the directional thermal test configuration, and Figure 7-8 shows the corresponding

measured thermal response for a temperature step of 50°C (25°C to 75°C).

T = TA = 25°C

Additional thermal

gradient from lower

temperature side

T = TTEST

Heat sourced

through 2oz.

Copper plane

HIGH

VOLTAGE

HV

FR-4 PCB

LV

HE

Figure 7-7. Directional Thermal Test Setup

Time (s)

0

25

50

75

100

125

-10

0

10 20 30 40 50 60 70 80 90 100 110 120

T63%  3.7s

T86%  33.0s

Final Te mperature

VOUT

Figure 7-8. Thermal Response (Directional)

Unlike the stirred liquid condition, thermal gradients exist across the package. As a result, the measured

response approaches a steady-state value below 100% of the applied temperature step. This occurs because

only part of the package is heated through the TSENSE pins while the remaining areas dissipate heat to the

surrounding environment.

The thermal response follows a first-order characteristic, reaching approximately 63% of the final value in about

3.7s, as shown in Figure 7-8. This indicates fast thermal coupling between the heat source and the internal

temperature sensor through the TSENSE pins.

The ISOTMP35R package is optimized to maximize thermal conduction through the TSENSE pins, enabling

efficient heat transfer from the heat source to the internal temperature sensor. Placing the TSENSE pins directly

at the high-voltage heat source enables fast response time and improved measurement accuracy compared to

non-isolated implementations that require remote sensor placement.

ISOTMP35R

SNIS244A – SEPTEMBER 2025 – REVISED MAY 2026

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