L5988D datasheet(37/52 Pages) STMICROELECTRONICS

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L5988D

Application information

Figure 19. Maximum continuous output current vs. duty cycle

6.6

Thermal considerations

The thermal design is important to prevent the thermal shutdown of the device if the junction

temperature goes above 150 °C. The three different sources of losses within the device are:

conduction losses due to the not negligible RDSON of the power switch; these are

equal to:

Equation 43

Where D is the duty cycle of the application. Note that the duty cycle is theoretically given by

the ratio between VOUT an VIN, but actually it is quite higher to compensate the losses of the

regulator. So the conduction losses increases compared with the ideal case.

switching losses due to power MOSFET turn ON and OFF; these can be

calculated as:

Equation 44

Where TRISE and TFALL represent the switching times of the power element that cause the

switching losses when driving an inductive load (see Figure 20). TSW is the equivalent

switching time.

PON

RDSON_HS IOUT



2 DR

DSON_LS

IOUT



–





PSW

VIN IOUT

TRISE TFALL



------------------------------------------- Fsw





VIN IOUT TSW FSW





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