33

LM5035C

www.ti.com

SNVS631D – JANUARY 2010 – REVISED OCTOBER 2016

Product Folder Links: LM5035C

Submit Documentation Feedback

Copyright © 2010–2016, Texas Instruments Incorporated

10 Power Supply Recommendations

The LM5035C can be used to control power levels up to 500 W; therefore, the current levels can be

considerable. Care must be taken in choosing components with the correct current rating which includes:

magnetic components, power MOSFETS and diodes, connectors, and wire sizes. Input and output capacitors

must have the correct ripple current rating. TI recommends using a multilayer PCB with a copper area chosen to

ensure the LM5035C operates below the maximum junction temperature. Full power loading must never be

attempted without providing for adequate cooling.

11 Layout

11.1 Layout Guidelines

The LM5035C current sense and PWM comparators are very fast, and respond to short duration noise pulses.

The components at the CS, COMP, SS, OVP, UVLO, DLY and the RT pins should be as physically close as

possible to the IC, thereby minimizing noise pickup on the PC board tracks.

Layout considerations are critical for the current sense filter. If a current sense transformer is used, both leads of

the transformer secondary should be routed to the sense filter components and to the IC pins. The ground side

of the transformer should be connected through a dedicated PC board track to the AGND pin, rather than

through the ground plane.

If the current sense circuit employs a sense resistor in the drive transistor source, low inductance resistors

should be used. In this case, all the noise sensitive, low-current ground tracks should be connected in common

near the IC, and then a single connection made to the power ground (sense resistor ground point).

The gate drive outputs of the LM5035C should have short, direct paths to the power MOSFETs to minimize

inductance in the PC board traces. The SR control outputs should also have minimum routing distance through

the pulse transformers and through the secondary gate drivers to the sync FETs.

The two ground pins (AGND, PGND) must be connected together with a short, direct connection, to avoid jitter

due to relative ground bounce.

If the internal dissipation of the LM5035C produces high junction temperatures during normal operation, the use

of multiple vias under the IC to a ground plane can help conduct heat away from the IC. Judicious positioning of

the PC board within the end product, along with use of any available air flow (forced or natural convection) will

help reduce the junction temperatures. If using forced air cooling, avoid placing the LM5035C in the airflow

shadow of tall components, such as input capacitors.