LM5006MMXSLASHNOPB datasheet(21/27 Pages) TI

21 / 27 page

OUT

1.1

LM5006

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SNVS646B – FEBRUARY 2011 – REVISED MARCH 2013

current switches between these two loops with each transition from on-time to off-time and back to on-time, it is

imperative that the ground end of C1 have a short and direct connection to D1’s anode (or Q1’s source), without

going through vias or a lengthy route. The power dissipation in the LM5006 can be approximated by determining

the total conversion loss (PIN – POUT), and then subtracting the power losses in D1 (or Q1), and in the inductor.

The power loss in the diode is approximately:

PD1 = IOUT x VF x (1–D)

where

•

VF is the diode’s forward voltage drop

•

D is the on-time duty cycle

(24)

The average power dissipation in the synchronous rectifier (Q1) is calculated from:

PQ1 = IOUT

2 x R

DS (on) x (1–D)

where

•

RDS(on) is the device’s on-resistance

•

D is the on-time duty cycle

(25)

The power loss in the inductor is approximately:

where

•

RL is the inductor DC resistance

•

the 1.1 factor is an approximation for the AC losses

(26)

If it is expected that the internal dissipation of the LM5006 will produce excessive junction temperatures during

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

wide PC board traces, where possible, can help conduct heat away from the IC. 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.

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LM5006MMX/NOPB Datasheet(PDF) 21 Page - Texas Instruments