LM5177DCPR datasheet(39/60 Pages) TI2

39 / 60 page

8.2.1 Design Requirements

Table 8-1 shows the intended input, output, and performance parameters for a typical design example.

Table 8-1. Design Parameters

Parameter

Value

VI minimum

VI typical = VI start-up

13.5V

VI maximum

36V

VO nominal

16V

PO maximum

128W

8.2.2 Detailed Design Procedure

8.2.2.1 Custom Design with WEBENCH Tools

Click here to create a custom design using the LM5177 device with the WEBENCH® Power Designer.

1. Start by entering your VIN, VOUT and IOUT requirements.

2. Optimize your design for key parameters like efficiency, footprint and cost using the optimizer dial and

compare this design with other possible solutions from Texas Instruments.

3. WEBENCH Power Designer provides you with a customized schematic along with a list of materials with real

time pricing and component availability.

4. In most cases, you will also be able to:

• Run electrical simulations to see important waveforms and circuit performance,

• Run thermal simulations to understand the thermal performance of your board,

• Export your customized schematic and layout into popular CAD formats,

• Print PDF reports for the design, and share your design with colleagues.

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

8.2.2.2 Frequency

The switching frequency of LM5177 is set by an RT resistor connected from the RT pin to AGND. The RT resistor

required to set the desired frequency is calculated using Equation 17. A 1% standard resistor of 78.7 kΩ is

selected for fSW = 400 kHz.

RRT = 1fsw−20ns ×30.3GΩs

(17)

8.2.2.3 Feedback Divider

The feedback voltage divider is found with Equation 18:

RFB,top= VVOUT −VREF

VREF ×RFB,bot

(18)

For the 16V output, an upper resistor of 71.5kΩ and a lower resistor of 4.7kΩ have been selected.

Table 8-2 shows an overview of a possible selection for the feedback divider resistors over common output

voltages.

Table 8-2. FB Pin Resistor Divider Examples with RFB,top = 71.5kΩ

VO – Target

RFB,bot – Calculation

RFB,bot – E48 Series

VO Nominal

Error from FB Resistor

17.9kΩ

17.8kΩ

5.02V

0.3%

8.94kΩ

9.09kΩ

8.87V

–1.5%

12V

6.50kΩ

6.49kΩ

12.02V

0.1%

16V

4.77kΩ

4.87kΩ

15.68V

–2.0%

24V

3.11kΩ

3.16kΩ

23.63V

–1.6%

www.ti.com

LM5177

SNVSBU4F – JUNE 2022 – REVISED JANUARY 2025

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