TPS54341_15 datasheet(38/48 Pages) TI

38 / 48 page

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)

(

)

TOT

A max

J max

TOT

COND

0.31 W

0.123 W

0.022 W

0.0018 W

0.457 W

12 V

146

0.0018 W

12 V

3nC

600 kHz

0.022 W

OUT

rise

12 V

600 kHz

3.5 A

4.9 ns

0.123 W

(

)

( )

OUT

COND

OUT

DS on

3.3 V

3.5 A

87 m

0.31 W

12 V

W ´

TPS54341

SLVSC61 – NOVEMBER 2013

www.ti.com

Power Dissipation Estimate

The following formulas show how to estimate the TPS54341 power dissipation under continuous conduction

mode (CCM) operation. These equations should not be used if the device is operating in discontinuous

conduction mode (DCM).

The power dissipation of the IC includes conduction loss (PCOND), switching loss (PSW), gate drive loss (PGD) and

supply current (PQ). Example calculations are shown with the 12 V typical input voltage of the design example.

(56)

spacer

(57)

spacer

(58)

spacer

(59)

Where:

IOUT is the output current (A).

RDS(on) is the on-resistance of the high-side MOSFET (Ω).

VOUT is the output voltage (V).

VIN is the input voltage (V).

ƒSW is the switching frequency (Hz).

trise is the SW pin voltage rise time and can be estimated by trise = VIN × 0.16 ns/V + 3 ns

QG is the total gate charge of the internal MOSFET

IQ is the operating nonswitching supply current

Therefore,

(60)

For given TA,

(61)

For given TJ(MAX) = 150°C

(62)

Where:

PTOT is the total device power dissipation (W).

TA is the ambient temperature (°C).

TJ is the junction temperature (°C).

RTH is the thermal resistance (°C/W).

TJ(MAX) is maximum junction temperature (°C).

TA(MAX) is maximum ambient temperature (°C).

There will be additional power losses in the regulator circuit due to the inductor ac and dc losses, the catch diode

and PCB trace resistance impacting the overall efficiency of the regulator.

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