APPLICATION NOTE
AN-00170-12
REFERENCE DESIGN OF A STEP-DOWN DC-DC CONVERTER
BASED ON THE XTR30011
By Gonzalo Picun, X-REL Semiconductor
AN-00170-12 rev1C 2019-02-07
1 of 5
PROPRIETARY INFORMATION
www.x-relsemi.com
© 2019 X-REL Semiconductor
TABLE OF CONTENTS
Introduction .......................................................................................................................................... 2
Buck converter schematic and critical points ....................................................................................... 2
Schematic............................................................................................................................................................................................. 2
General Recommendations ................................ ................................................................................................ .................................. 3
Important Notice & Disclaimer ............................................................................................................. 5
Contact Us ............................................................................................................................................. 5
ABSTRACT
This application note describes a reference design demo board implementing a step-down (buck) DC-DC converter based on the
XTR30011 PWM controller and on power N-MOS transistors with drivers of the XTR20410 family. The implemented reference design can
be adapted for other parts of the family, such as XTR30012 and XTR30015.
In this application note it is presented a general schematic as well as values for each device. How to size those devices derive from the
general theory of step-down converters and is covered in another application note. General documentation about the sizing of step-down
DC-DC converters can also be found on the web.
REFERENCE DESIGN OF A STEP-DOWN DC-DC CON-
VERTER BASED ON THE XTR30011
AN-00170-12 rev1C 2019-02-07
2 of 5
PROPRIETARY INFORMATION
www.x-relsemi.com
© 2019 X-REL Semiconductor
INTRODUCTION
The purpose of this document is to present an implementation of a voltage mode DCDC buck converter. The controller is based on the
XTR-30011 PWM controller and the power part (driver & power MOSEFTs) is chosen from the XTR20410 family.
The purpose is not to explain how to size each element, but to give information for the board implementation and for the test of such board.
BUCK CONVERTER SCHEMATIC AND CRITICAL POINTS
Schematic
Figure 1 shows the schematic of the proposed DC-DC Buck converter. It is based on a XTR30011 PWM controller and two XTR2041x N-
MOS power transistors with integrated driver. All other components are passive parts. The shown schematic supposes a maximum input
voltage of 30V, but it can be extended to 35V provided XTR2081x devices are used as power elements.
The choice of the specific XTR2041x part used depends on the required output current range. As they all have the same pinout and pack-
age size, the PCB will be sized for the highest voltage & current level.
This demonstrator allows different operation mode thanks to the terminals SYNC, PSkipTh and DCLimit as well as settings on switches
controlling ENABLE, PSkipEn, AsyncEn and LPMode, together with several optional passive components (represented in green and orange
in
Figure 1). See XTR30010 datasheet for an explanation on each functional feature.
The demonstrator also gives access to circuit outputs (PGood, CKOUT) as well as several test points (in dark red) to monitor the good op-
eration of the converter.
The schematic shown in
Figure 1 shows optional passive components in different colors. Orange devices must be shorted if not present. Green devices must be left
open if not used.
Table 1 at the end of this document provides typical values for each passive element required for this board.
General Recommendations
Printed Circuit Board
High temperature compliant (Polyimide or Rogers, Tg=260°C or higher)
Use four (4) copper layers for routing with intermediate GND plane. The second inner layer should be used for VIN and VDD dis-
tribution.
Copper thickness 35µm.
Be careful with vias at high temperature when more than 2 layers. These vias could deteriorate when soldering components (i.e.
bad contact if connected to middle layer).
Implement wo ground planes (GND & PGND) that will have to be connected only in one point (with a zero resistor that can sus-
tain large current). Outside of this common point, the PCB can include the possibility to connect several decoupling capacitance
between both half ground planes GND & PGND.
Add various GND and PGND test points all over the board for easy connection of a probe grounds.
The PCB can see DC & switched voltages up to 80V.
Use of labels on the PCB to clearly identify tespoints.
For EMI considerations, avoid loops and be very clean with ground planes.
Prefer SMD components whenever possible
For through hole parts, consider soldering on both sides.
Give flexibility on the PCB for Lout and Cout (several fingerprints).
Think about the possibility to relax thermal/mechanical constraints on the PCB.
Keep distance between wires that are at very different voltage level.
No soldering of passive element under the ICs.
Finishing of the outermost copper layers should be NiAu or other high temperature compatible finishing.
Specific Nodes
The PCB lines corresponding to thick lines in the schematic must be large enough for the output current level required.
The source and drain terminals of the XTR20401x devices must be sized according this current level.
Pay special attention to the routing and laying out of the SW node. This node see high dV/dt and dI/dt giving rise to high current
and voltage spikes if the parasitic capacitor and inductance are large. The life of the output transistors and drivers strongly de-
pend on how neat this node is laid out.
The PVDD and PGND terminals of the XTR30011 must be compatible with peak currents of 1A and minimize parasitic inductance
in series with these terminals.
The recommendation just above applies also for signals HDrv and LDrv.