K =

4.8W

4.8W + 0.6W

= 89%

K =

POUT

POUT + PTOTAL

x 100%

PCAP =

(1.924A)

2 x 24 m:

1

2

IRMS_RIP = IOUT x

D(1 - D)

PCAP =

(IRMS_RIP)

2 x ESR

n

2

28

LM2743

SNVS276I – APRIL 2004 – REVISED FEBRUARY 2019

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Copyright © 2004–2019, Texas Instruments Incorporated

Typical Applications (continued)

PCND2 = (4A)

2 x 13 mΩ x 1.3 x (1 - 0.364)

(58)

PCND = 98.42 mW + 172 mW = 270.42 mW

(59)

There are few additional losses that are taken into account:

The following equations show IC Operating Loss (PIC).

PIC = IQ_VCC x VCC,

(60)

where IQ-VCC is the typical operating VCC current

PIC= 1.5 mA x 3.3V = 4.95 mW

(61)

The following equations show FET Gate Charging Loss (PGATE).

PGATE = n x VCC x QGS x fSW

(62)

PGATE = 2 x 3.3 V x 3 nC x 300 kHz

(63)

PGATE = 5.94 mW

(64)

The value n is the total number of FETs used and QGS is the typical gate-source charge value, which is 3 nC. For

the FDS6898A the gate charging loss is 5.94 mW.

The following equations show Input Capacitor Loss (PCAP).

where

(65)

(66)

Here n is the number of paralleled capacitors, ESR is the equivalent series resistance of each, and PCAP is the

dissipation in each. So for example if we use only one input capacitor of 24 m

Ω.

(67)

PCAP = 88.8 mW

(68)

The following equation shows Output Inductor Loss (PIND).

PIND = I

2

OUT x DCR

(69)

where DCR is the DC resistance. Therefore, for example

PIND = (4A)

2 x 11 mΩ

(70)

PIND = 176 mW

(71)

The following equations show Total System Efficiency.

PTOTAL = PFET + PIC + PGATE + PCAP + PIND

(72)

(73)

(74)