L5988D datasheet(40/52 Pages) STMICROELECTRONICS

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Application information

L5988D

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DocID15324 Rev 4

Figure 22. Estimation of the internal power losses (VIN = 5 V, VOUT = 1.2 V,

fSW = 400 kHz)

In applications where the current to the output is pulsed, the thermal impedance should be

considered instead of the thermal resistance. Also, in these conditions, the current

limitations described in Section 6.5 on page 36 are no more valid since they are related to

continuous output current delivery.

The thermal impedance of the system could be much lower than the thermal resistance,

which is a static parameter. As a consequence the maximum power losses can be higher

than 2.5 W if a pulsed output power is requested from the load:

Equation 48

So, depending on the pulse duration and its frequency, the maximum output current (even

more than 5 A) can be delivered to the load.

The characterization of the thermal impedance is strictly dependent on the layout of the

board. In Figure 23. the measurement of the thermal impedance of the evaluation board of

the L5988D is provided.

PMAX t

T

ZTH t

-----------------

TJ MAX TAMB

–

ZTH t

--------------------------------------

L5988D Datasheet(PDF) 40 Page - STMicroelectronics