PCOND= (IOUT

2 x D)

1

3

1 +

x

iL

IOUT

2

RDSON

LM2830, LM2830-Q1

SNVS454E – AUGUST 2006 – REVISED DECEMBER 2014

www.ti.com

Another significant external power loss is the conduction loss in the output inductor. The equation can be

simplified to:

PIND = IOUT

2 × R

DCR

(20)

The conduction loss of the LC2830 device is mainly associated with the internal PFET:

(21)

If the inductor ripple current is fairly small, the conduction losses can be simplified to:

PCOND = IOUT

2 × R

DSON × D

(22)

Switching losses are also associated with the internal PFET. They occur during the switch on and off transition

periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss

is to empirically measuring the rise and fall times (10% to 90%) of the switch at the switch node.

Switching Power Loss is calculated as follows:

PSWR = 1/2(VIN × IOUT × FSW × TRISE)

(23)

PSWF = 1/2(VIN × IOUT × FSW × TFALL)

(24)

PSW = PSWR + PSWF

(25)

Another loss is the power required for operation of the internal circuitry:

PQ = IQ × VIN

(26)

IQ is the quiescent operating current, and is typically around 3.3 mA for the 1.6-MHz frequency option.

Table 2 lists typical application power losses.

Table 2. Power Loss Tabulation

Design Parameter

Value

Design Parameter

Value

VIN

5.0 V

VOUT

3.3 V

POUT

3.3 W

IOUT

1.0A

VD

0.45 V

PDIODE

150 mW

FSW

1.6 MHz

IQ

3.3 mA

PQ

17 mW

TRISE

4 nS

PSWR

6 mW

TFALL

4 nS

PSWF

6 mW

RDS(ON)

150 m

Ω

PCOND

100 mW

INDDCR

70 m

Ω

PIND

70 mW

D

0.667

PLOSS

345 mW

η

88%

PINTERNAL

125 mW

ΣPCOND + PSW + PDIODE + PIND + PQ = PLOSS

(27)

ΣPCOND + PSWF + PSWR + PQ = PINTERNAL

(28)

PINTERNAL = 125mW

(29)

16

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