LM27341_15 datasheet(20/44 Pages) TI

20 / 44 page

K =

POUT

POUT + PLOSS

6.6 W

6.6 W + 1.499 W

= 81 %

LM27341, LM27342, LM27341-Q1, LM27342-Q1

SNVS497E – NOVEMBER 2008 – REVISED APRIL 2013

www.ti.com

TOTAL POWER LOSSES

Total power losses are:

PLOSS = PCOND + PSWR + PSWF + PQ + PBOOST + PDIODE + PIND

(37)

Losses internal to the LM27341/LM27342 are:

PINTERNAL = PCOND + PSWR + PSWF + PQ + PBOOST

(38)

EFFICIENCY CALCULATION EXAMPLE

Operating conditions are:

VIN = 12V

VOUT = 3.3V

IOUT = 2A

fSW = 2 MHz

VD1 = 0.5V

RDCR = 20 mΩ

Internal Power Losses are:

PCOND = IOUT

2 x R

DSON x D

= 2

2 x 0.15Ω x 0.314

= 188 mW

(39)

PSW = (VIN x IOUT x fSW x tFALL)

= (12V x 2A x 2 MHz x 10ns)

= 480 mW

(40)

PQ = IQ x VIN

= 2.4 mA x 12V

= 29 mW

(41)

PBOOST = IBOOST x VBOOST

= 8.2 mA x 4.5V

= 37 mW

(42)

PINTERNAL = PCOND + PSW + PQ + PBOOST= 733 mW

(43)

Total Power Losses are:

PDIODE = VD1 x IOUT (1 - D)

= 0.5V x 2 x (1 - 0.314)

= 686 mW

(44)

PIND = IOUT

2 x R

DCR

= 2

2 x 20 mΩ

= 80 mW

(45)

PLOSS = PINTERNAL + PDIODE + PIND = 1.499 W

(46)

The efficiency can now be estimated as:

(47)

With this information we can estimate the junction temperature of the LM27341/LM27342.

CALCULATING THE LM27341/LM27342 JUNCTION TEMPERATURE

Thermal Definitions:

TJ = IC junction temperature

TA = Ambient temperature

RθJC = Thermal resistance from IC junction to device case

RθJA = Thermal resistance from IC junction to ambient air

Submit Documentation Feedback

Product Folder Links: LM27341 LM27342 LM27341-Q1 LM27342-Q1

LM27341 Datenblatt(PDF) 20 Page - Texas Instruments

LM27341 Datenblatt(HTML) 20 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datenblatt Download

Link URL