Datasheet

BuckLOWERFET OUT DS(on) F OUT d SW

P (I ) r (1 TC) (1 D) V I (2 t ) f= ´ + ´ - + ´ ´ ´ ´

IN OUT

BuckTOPFET OUT DS(on) r f SW

V I

P (I ) r (1 TC) D (t t ) f

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= ´ + ´ + ´ + ´

ç ÷

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TPS43330-Q1

TPS43332-Q1

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SLVSA82E –MARCH 2011–REVISED APRIL 2013

BuckX High-Side and Low-Side N-Channel MOSFETs

An internal supply, which is 5.8 V typical under normal operating conditions, provides the gate-drive supply for

these MOSFETs. The output is a totem pole, allowing full-voltage drive of V

REG

to the gate with peak output

current of 1.5 A. The reference for the high-side MOSFET is a floating node at the phase terminal (PHx), and the

reference for the low-side MOSFET is the power-ground (PGNDx) terminal. For a particular application, select

these MOSFETs with consideration for the following parameters: r

DS(on)

, gate charge Qg, drain-to-source

breakdown voltage BVDSS, maximum dc current IDC(max), and thermal resistance for the package.

The times t

and t

denote the rising and falling times of the switching node and have a relationship to the gate-

driver strength of the TPS43330-Q1 and TPS43332-Q1 and to the gate Miller capacitance of the MOSFET. The

first term denotes the conduction losses, which are minimimal when the on-resistance of the MOSFET is low.

The second term denotes the transition losses, which arise due to the full application of the input voltage across

the drain-source of the MOSFET as it turns on or off. Transition losses are lower at low currents and when the

switching time is low.

In addition, during the dead time t

when both the MOSFETs are off, the body diode of the low-side MOSFET

conducts, increasing the losses. The second term in the preceding equation denotes this. Using external

Schottky diodes in parallel with the low-side MOSFETs of the buck converters helps to reduce this loss.

Note: r

DS(on)

has a positive temperature coefficient, and the TC term for r

DS(on)

accounts for that fact. TC = d ×

ΔT[°C]. The temperature coefficient d is available as a normalized value from MOSFET data sheets and can

have an assumed starting value of 0.005 per ºC.

Product Folder Links: TPS43330-Q1 TPS43332-Q1