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LM5010A, LM5010A-Q1

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SNVS376F – OCTOBER 2005 – REVISED MAY 2016

Product Folder Links: LM5010A LM5010A-Q1

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Copyright © 2005–2016, Texas Instruments Incorporated

9 Power Supply Recommendations

The LM5010Ax is designed to operate with an input power supply capable of supplying a voltage range from 6 V

to 75 V. The input power supply must be well-regulated and capable of supplying sufficient current to the

regulator during peak load operation. Also, like in all applications, the power-supply source impedance must be

small compared to the module input impedance to maintain the stability of the converter.

10 Layout

10.1 Layout Guidelines

The LM5010Ax regulation, overvoltage, and current limit comparators are very fast, and respond to short

duration noise pulses. Therefore, layout considerations are critical for optimum performance. The layout must be

as neat and compact as possible, and all the components must be as close as possible to their associated pins.

The two major current loops have currents which switch very fast, and so the loops should be as small as

possible to minimize conducted and radiated EMI. The first loop is that formed by C1 (CIN), through the VIN to

SW pins, L1 (LIND), C2 (COUT), and back to C1. The second loop is that formed by D1, L1, C2, and the SGND and

ISEN pins. The ground connection from C2 to C1 should be as short and direct as possible, preferably without

going through vias. Directly connect the SGND and RTN pin to each other, and they should be connected as

directly as possible to the C1/C2 ground line without going through vias. The power dissipation within the IC can

be approximated by determining the total conversion loss (PIN - POUT), and then subtracting the power losses in

the free-wheeling diode and the inductor. The power loss in the diode is approximately Equation 27.

PD1 = IO × VF × (1 – D)

where

•

IO is the load current

•

VF is the diode’s forward voltage drop

•

D is the duty cycle

(27)

The power loss in the inductor is approximately Equation 28.

PL1 = IO

2 × R

L × 1.1

where

•

RL is the inductor’s DC resistance

•

the 1.1 factor is an approximation for the AC losses

(28)

If it is expected that the internal dissipation of the LM5010Ax will produce high junction temperatures during

normal operation, good use of the PC board’s ground plane can help considerably to dissipate heat. The

exposed pad on the IC package bottom should be soldered to a ground plane, and that plane should both extend

from beneath the IC, and be connected to exposed ground plane on the board’s other side using as many vias

as possible. The exposed pad is internally connected to the IC substrate. The use of wide PC board traces at the

pins, where possible, can help conduct heat away from the IC. The four no connect pins on the HTSSOP

package are not electrically connected to any part of the IC, and may be connected to ground plane to help

dissipate heat from the package. Judicious positioning of the PC board within the end product, along with the use

of any available air flow (forced or natural convection) can help reduce the junction temperature.