LM46001 datasheet(28/56 Pages) TI2

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FBB

FBT

OUT

LM46001

SNVSA46B – JUNE 2014 – REVISED JANUARY 2018

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8.2.1 Design Requirements

A detailed design procedure is described based on a design example. For this design example, use the

parameters listed in Table 3 as the input parameters.

Table 3. Design Example Parameters

DESIGN PARAMETER

VALUE

Input voltage VIN

24 V typical, range from 3.8 V to 60 V

Output voltage VOUT

3.3 V

Input ripple voltage

400 mV

Output ripple voltage

30 mV

Output current rating

1 A

Operating frequency

500 kHz

Soft-start time

10 ms

8.2.2 Detailed Design Procedure

8.2.2.1 Custom Design With WEBENCH® Tools

Click here to create a custom design using the LM46001 device with the WEBENCH® Power Designer.

1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.

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

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

•

Run electrical simulations to see important waveforms and circuit performance

•

Run thermal simulations to understand board thermal performance

•

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.

8.2.2.2 Output Voltage Setpoint

The output voltage of the LM46001 device is externally adjustable using a resistor divider network. The divider

network is comprised of top feedback resistor RFBT and bottom feedback resistor RFBB. The following equation is

used to determine the output voltage of the converter:

(11)

Choose the value of the RFBT to be 1 MΩ to minimize quiescent current to improve light load efficiency in this

application. With the desired output voltage set to be 3.3 V and the VFB = 1.016 V, the RFBB value can then be

calculated using Equation 11. The formula yields a value of 444.83 kΩ. Choose the closest available value of 442

kΩ for the RFBB. See Adjustable Output Voltage for more details.

8.2.2.3 Switching Frequency

The default switching frequency of the LM46001 device is set at 500 kHz when RT pin is open circuit. The

switching frequency is selected to be 500 kHz in this application for one less passive components. If other

frequency is desired, use Equation 12 to calculate the required value for RT.

RT(kΩ) = 40200 / Freq (kHz) – 0.6

(12)

For 500 kHz, the calculated RT is 79.8 kΩ and standard value 80.6 kΩ can also be used to set the switching

frequency at 500 kHz.

LM46001 Datasheet(PDF) 28 Page - Texas Instruments

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