RAMP

RT1

CS

OUTB

PGND

SS

RES

UVLO

COMP

FB

RT2

REF

VIN

VCC

OUTA

AGND

LM5037

From VIN

From FB

From CS

To GDA

To GDB

LM5037

www.ti.com

SNVS578D – NOVEMBER 2008 – REVISED MAY 2015

10 Layout

10.1 Layout Guidelines

The LM5037 device current sense and PWM comparators are very fast, and respond to short duration noise

pulses. Place components for the CS, COMP, SS, UVLO, RT2 and the RT1/SYNC pins as physically close as

possible to the device. This placement minimizes noise pickup on the PC board trace inductances.

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 device pins. The ground

side of the transformer should be connected via a dedicated PC board trace 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 trace should be connected in common

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

While employing current mode control, RAMP pin capacitor and CS pin capacitor must be placed close to the

device. Also, a short direct trace should be employed to connect RAMP capacitor to the CS pin.

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

inductance in the PC board 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 device produces high junction temperatures during normal operation, the use of

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

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

convection) helps reduce the junction temperatures. If using forced air cooling, avoid placing the device in the

airflow shadow of tall components, such as input capacitors.

10.2 Layout Example

Figure 35. LM5037 Board Layout

Copyright © 2008–2015, Texas Instruments Incorporated

Submit Documentation Feedback

33

Product Folder Links: LM5037