R5975D datasheet(32/47 Pages) STMICROELECTRONICS

32 / 47 page

Application information

R5975D

32/47

DocID026878 Rev 1

8.4

RMS current of the embedded power MOSFET

As the R5975D embeds the high side switch, the internal power dissipation is sometimes

the bottleneck for the output current capability (refer to Section 8.3 for the estimation of the

operating temperature).

Nevertheless, as mentioned in Description on page 1, the device can manage a continuous

output current of 3 A in most of the application conditions.

However, the rated maximum RMS current of the power elements is 2 A, where:

Equation 31

and the real duty cycle D:

Equation 32

Fixing the limit of 2 A for IRMS HS, the maximum output current can be derived, as illustrated

in Figure 18.

Figure 18. Maximum continuous output current vs. duty cycle

8.5

Short-circuit protection

In overcurrent protection mode, when the peak current reaches the current limit, the device

reduces the TON down to its minimum value (approximately 250 nsec) and the switching

frequency to approximately one third of its nominal value even when synchronized to an

external signal (see Section 5.4: Current protection on page 14). In these conditions, the

duty cycle is strongly reduced and, in most applications, this is enough to limit the current to

ILIM. In any event, in case of heavy short-circuit at the output (VO = 0 V) and depending on

the application conditions (VCC value and parasitic effect of external components), the

current peak could reach values higher than ILIM.

IRMS HS

ILOAD



VOUT

RDS (on) LS DCR

 I

LOAD



VIN

RDS (on) LS RDS (on) HS

–

 I

LOAD



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