LM46002PWPR datasheet(40/54 Pages) TI2

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VIN

PGND

CIN

VIN

COUT

VOUT

High di/dt

current

BUCK

CONVERTER

LM46002

SNVSA13C – APRIL 2014 – REVISED APRIL 2019

www.ti.com

Product Folder Links: LM46002

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9 Power Supply Recommendations

The LM46002 is designed to operate from an input voltage supply range between 3.5 V and 60 V. This input

supply must be able to withstand the maximum input current and maintain a voltage above 3.5 V. The resistance

of the input supply rail must be low enough that an input current transient does not cause a high enough drop at

the LM46002 supply voltage that can cause a false UVLO fault triggering and system reset.

If the input supply is located more than a few inches from the LM46002 additional bulk capacitance may be

required in addition to the ceramic bypass capacitors. The amount of bulk capacitance is not critical, but a 47-µF

or 100-µF electrolytic capacitor is a typical choice.

10 Layout

The performance of any switching converter depends as much upon the layout of the PCB as the component

selection. The following guidelines will help users design a PCB with the best power conversion performance,

thermal performance, and minimized generation of unwanted EMI.

10.1 Layout Guidelines

1. Place ceramic high frequency bypass CIN as close as possible to the LM46002 VIN and PGND pins.

Grounding for both the input and output capacitors must consist of localized top side planes that connect to

the PGND pins and PAD.

2. Place bypass capacitors for VCC and BIAS close to the pins and ground the bypass capacitors to device

ground.

3. Minimize trace length to the FB pin. Both feedback resistors, RFBT and RFBB should be located close to the

FB pin. Place CFF directly in parallel with RFBT. If VOUT accuracy at the load is important, make sure VOUT

sense is made at the load. Route VOUT sense path away from noisy nodes and preferably through a layer on

the other side of a shieldig layer.

4. Use ground plane in one of the middle layers as noise shielding and heat dissipation path.

5. Have a single point ground connection to the plane. Route the ground connections for the feedback, soft

start, and enable components to the ground plane. This prevents any switched or load currents from flowing

in the analog ground traces. If not properly handled, poor grounding can result in degraded load regulation or

erratic output voltage ripple behavior.

6. Make VIN, VOUT and ground bus connections as wide as possible. This reduces any voltage drops on the

input or output paths of the converter and maximizes efficiency.

7. Provide adequate device heat sinking. Use an array of heat-sinking vias to connect the exposed pad to the

ground plane on the bottom PCB layer. If the PCB has multiple copper layers, these thermal vias can also be

connected to inner layer heat-spreading ground planes. Ensure enough copper area is used for heat sinking

to keep the junction temperature below 125°C.

10.1.1 Compact Layout for EMI Reduction

Radiated EMI is generated by the high di/dt components in pulsing currents in switching converters. The larger

area covered by the path of a pulsing current, the more electromagnetic emission is generated. The key to

minimize radiated EMI is to identify the pulsing current path and minimize the area of the path. In Buck

converters,the pulsing current path is from the VIN side of the input capacitors to HS switch, to the LS switch, and

then return to the ground of the input capacitors, as shown in Figure 100.

Figure 100. Buck Converter High di / dt Path

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