AN4402 datasheet(28/39 Pages) STMICROELECTRONICS

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Energy capability and load compatibility

AN4402

28/39

DocID025557 Rev 1

The L99MC6 provides data under the following conditions:

•

Single pulse, with TJSTART = 150°C: it is applicable for switch-off conditions, which

occur rarely

•

Repetitive pulse with TJSTART=125°C: it is applicable for switch-off conditions, with a

high occurrence rate. It is applicable with time between two occurrences is long enough

to allow the junction temperature to decrease to 125°C

•

Repetitive pulse with TJSTART=100°C: it is applicable for switch-off conditions, with a

high occurrence rate. It is applicable if the time between two occurrences is long

enough to allow the junction temperature to decrease to 100°C

Even if EDEMAG dissipated in the application conditions is below the maximal energy

allowed by the device with the same inductance (at RL = 0 Ω and RL = 13.5 V), it does not

automatically mean that the load compatibility is given. Indeed, it is possible that a lower

EDEMAG in the application conditions is dissipated in a shorter time (tDEMAG), resulting in a

higher power dissipation and therefore a higher junction temperature increase.

The developer must verify that the energy which has been calculated in the step1 is below

the maximum energy capability of the device with the corresponding demagnetization time.

Step3: Confirmation by measurements

It is recommended to perform bench tests in the real application conditions.

This phase is key because it allows verifying that the load data (inductance and resistance),

which are used for the calculations in step1 and step2, are representative of the real

application. It avoids either an underdimensioning of the system and therefore unexpected

failures, or overdimensioning with the involved extra-costs for external protection devices.

Some sources of mismatch between calculations and measurement can be:

•

A mismatch between the calculation RL and the real RL. Indeed, RL is in general

specified only at room temperature. Since the winding is made of copper, its resistance

is subject to variations due to temperature.

•

measuring the inductance with a LCR meter by applying a small AC signal does not

take into account the impact of the DC voltage bias of the inductance in the real

application

•

the decrease of the inductance at high currents (saturation of the inductor) might not be

taken into account

•

self-heating effects of the load on RL and L are not considered

4.2

Example of L99MC6 driving a relay with a low-side driver

Table 12. Application conditions

Parameter

Value

Type of output

Configurable output (OUT1,2 or 3), configured as low-side switch

L512 mH

400

VCL_LS

35V (typical value of the L99MC6)

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