RHRPM4424 datasheet(13/31 Pages) STMICROELECTRONICS

13 / 31 page

It is indicated in the below equation:

Equation 2

When an application is designed using the RHRPM4424, the effect of external gate resistors on the power

dissipated by the driver has to be taken into account. External gate resistors help the device to dissipate the

switching power since the same power, PSW, is shared between the internal driver impedance and the external

resistor.

In Figure 7. Minimum gate resistance, the MOSFET driver can be represented by a push-pull output stage with

two different MOSFETs:

•

PDMOS to drive the external gate to high level

•

NDMOS to drive the external gate to low level (with RDS(on): Rhi, Rlo)

The external MOSFET can be represented as Cgate capacitance, which stores QG gate charge required by the

external MOSFET to reach VCC driving voltage. This capacitance is charged and discharged at FSW frequency.

PSW total power is dissipated among the resistive components distributed along the driving path. According to the

external gate resistance and the intrinsic MOSFET gate resistance, the driver only dissipates a PSW portion as

follows (per driver):

Equation 3

P S W

--- Cga te VCC

(

)

2 F

S W

Rhi

Rhi Rg Rloa d

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

Rlo

Rlo Rg Rloa d

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









⋅

The total dissipated power from the driver is given by PTOT = PDC + 2*PSW.

Figure 8. Driver and load equivalent circuits

VCC

Rhi = Rds_on of the high side integrated switch

Rlo = Rds_on of the low side integrated switch

OUT_x

PGND

Gate

Driver

Rload

Cgate

MOSFET

Equivalent circuit

Rhi

Rlo

GIPD180120161338MT

RHRPM4424

Power dissipation

DS11485 - Rev 7

page 13/31

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