ISL58831

10

FN7440.1

January 28, 2016

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Furthermore, the case-to-ambient thermal coefficient may not be

known precisely.

To assist in worst case conditions, it is possible to monitor the

silicon temperature of the ISL58831 by forcing current into the

Since ENABLE = HI is necessary for normal operation, the device

can be operated as it would be in the real-life applications, while

the temperature is monitored. The ISL58831 has been calibrated

with a 1MΩ resistor to +10V connected in series with the ENABLE

pin, which results in an input current of approximately 4.5µA.

Figure 7 allows the silicon temperature to be determined directly.

The graph shows the measured ENABLE pin to VDD pin

differential voltage, which shows a linear voltage sensitivity of

-2.26mV/°C. Users may wish to measure their specific part at

+20°C (no warm-up) to allow for any statistical/process

distribution, but the method is reliable and accurate.

By applying this method to the ISL58831 in an actual

application, users can measure the silicon temperature under all

operating conditions to determine whether their thermal

engineering is sufficient. The thermal resistance of the QFN24 is

+140°C/W when tested on a standard JEDEC JESD51-3 (single

layer) test board. When using a standard JEDEC JESD51-7 (four

layer) test board, the thermal resistance is +112°C/W. Actual

thermal resistance is highly dependent on circuit board layout

considerations.

Temperature Measurement Set-Up and

Results

conditions. Suppose result (must be after thermal equilibrium

Now one can calculate the temperature rise of (450 to 580)/

-2.26 = +57°C. Using the power dissipation of

calculated.

SILICON TEMPERATURE (°C)

0

25

125

150

75

600

550

450

400

350

300

250

500

50

100

ENA WITH 1MΩ TO +10V

FIGURE 7. ISL58831 ON-CHIP THERMOMETER

ENABLE

ISL58831

V

1M

+10V

+5V