Texas Instruments Evaluation Board for LM3150-500 kHz - SIMPLE SWITCHER® CONTROLLER, 42V Synchronous Step-Down LM3150-50 LM3150-500EVAL/NOPB 데이터 시트
제품 코드
LM3150-500EVAL/NOPB
Powering and Loading Considerations
3.2
Testing the Fixed Version Parts
The fixed output versions can also be mounted on the LM3150 evaluation boards with few modifications to
the default configuration as indicated below. This is achievable because pins 7 and 8 are not internally
connected on the fixed version parts.
the default configuration as indicated below. This is achievable because pins 7 and 8 are not internally
connected on the fixed version parts.
1. Replace U1, LM3150, with a fixed version part such as the LM3152
2. Short Rfb2
3. Remove Rfb1
4. Remove Cff
Ensure that the remaining components on the evaluation board will meet your design specifications by
using the provided circuit calculator tools.
using the provided circuit calculator tools.
3.3
Alternate Ripple Injection
Certain designs may benefit from another ripple injection technique that utilizes a resistor and capacitor to
integrate the voltage across the inductor and then couple that signal through a capacitor to the FB pin.
This technique is commonly found in COT controllers and may benefit designs that have high output
voltage such as 12V and a low-side FET that has a low R
integrate the voltage across the inductor and then couple that signal through a capacitor to the FB pin.
This technique is commonly found in COT controllers and may benefit designs that have high output
voltage such as 12V and a low-side FET that has a low R
DSON
and require low output voltage ripple. The
evaluation board allows for this configuration allowing the placement of Rr, Cr, and Cac. After the proper
components for Rr, Cr, and Cac have been chosen mount them on the evaluation board and remove Cff.
components for Rr, Cr, and Cac have been chosen mount them on the evaluation board and remove Cff.
A quick efficiency check is the best way to confirm that everything is operating properly. If something is
amiss you can be reasonably sure that it will affect the efficiency adversely. Few parameters can be
incorrect in a switching power supply without creating losses and potentially damaging heat.
amiss you can be reasonably sure that it will affect the efficiency adversely. Few parameters can be
incorrect in a switching power supply without creating losses and potentially damaging heat.
3.4
Improving Efficiency
It is also well known that efficiency may be improved slightly by placing a Schottky diode across the low-
side FET. The Schottky diode has a much lower forward voltage drop than the internal diode of the FET
and a faster turn-on time. This evaluation board allows for a Schottky diode to be placed on footprint D1.
side FET. The Schottky diode has a much lower forward voltage drop than the internal diode of the FET
and a faster turn-on time. This evaluation board allows for a Schottky diode to be placed on footprint D1.
The internal VCC regulator provides a supply voltage to both the high-side and low-side FET drivers. The
high-side FET driver receives it’s supply voltage through a internal diode that has a forward voltage drop
as high as 1V. This may impact the drivers ability to turn on the high-side FET fully and therefore cause a
loss in efficiency depending upon which FET is chosen. The footprint Dbst allows for placement of a
Schottky diode that will have a much smaller forward drop and therefore increase the driver supply voltage
and allow for improved efficiency for certain FETs.
high-side FET driver receives it’s supply voltage through a internal diode that has a forward voltage drop
as high as 1V. This may impact the drivers ability to turn on the high-side FET fully and therefore cause a
loss in efficiency depending upon which FET is chosen. The footprint Dbst allows for placement of a
Schottky diode that will have a much smaller forward drop and therefore increase the driver supply voltage
and allow for improved efficiency for certain FETs.
3.5
Output Voltage Ripple Measurement
The output voltage ripple measurement is usually taken directly across the output capacitors utilizing
extremely short scope probe leads. To help make this measurement slightly easier, a footprint Cf has
been included that will allow for a 1 µF or less 0805 or 1206 capacitor to be mounted directly across the
output voltage terminals that will allow for approximate measurement of the ripple voltage.
extremely short scope probe leads. To help make this measurement slightly easier, a footprint Cf has
been included that will allow for a 1 µF or less 0805 or 1206 capacitor to be mounted directly across the
output voltage terminals that will allow for approximate measurement of the ripple voltage.
3
SNVA371D – September 2008 – Revised May 2013
AN-1900 LM3150 Evaluation Boards
Copyright © 2008–2013, Texas Instruments Incorporated