LM2743MTCSLASHNOPB datasheet(20/44 Pages) TI2

20 / 44 page

PCAP =

(IRMS_RIP)

2 x ESR

IRMS_RIP = IOUT x

D(1 - D)

D =

VOUT + VSWL

VIN - VSWH + VSWL

LM2743

SNVS276I – APRIL 2004 – REVISED FEBRUARY 2019

www.ti.com

Product Folder Links: LM2743

Submit Documentation Feedback

Typical Applications (continued)

•

Export customized schematic and layout into popular CAD formats

•

Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

8.2.1.2.2

Duty Cycle Calculation

The complete duty cycle for a buck converter is defined with Equation 16:

(16)

where VSWL and VSWH are the respective forward voltage drops that develop across the low side and high side

MOSFETs. Assuming the inductor ripple current is 20% to 30% of the output current, therefore:

VSWL = IOUT x RDS(ON)LOW (Low-Side MOSFET)

(17)

VSWH = IOUT x RDS(ON)HIGH (High-Side MOSFET)

(18)

To calculate the maximum duty cycle use the estimated 'hot' RDS(on) value of the MOSFETs, the minimum input

voltage, and maximum load. As shown in Figure 31, the worst case maximum duty cycles of the LM2743 occurs

at 125°C junction temperature vs VCC (IC control section voltage). Ensure that the operating duty cycle is below

the curve in Figure 31, if this condition is not satisfied, the system will be unable to develop the required duty

cycle to derive the necessary system power and so the output voltage will fall out of regulation.

Figure 31. Maximum Duty Cycle vs VCC

TJ = 125°C

8.2.1.2.3

Input Capacitor

The input capacitors in a Buck converter are subjected to high stress due to the input current trapezoidal

waveform. Input capacitors are selected for their ripple current capability and their ability to withstand the heat

generated since that ripple current passes through their ESR. Input rms ripple current is approximately:

(19)

The power dissipated by each input capacitor is:

(20)

LM2743MTC/NOPB Datasheet(PDF) 20 Page - Texas Instruments

LM2743MTC/NOPB Datasheet(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

Datasheet Download

Link URL