User's Guide
SNVA102A – October 2005 – Revised April 2013
AN —1356 LM2743 Evaluation Board
1
Introduction
This application notes describes the LM2743 printed circuit board (PCB) design and provides an example
typical application circuit. The demo board allows component design flexibility in order to demonstrate the
versatility of the LM2743 IC.
The demo board contains a voltage-mode, high-speed synchronous buck regulator controller. Though the
control sections of the IC are rated for 3 to 6V (VCC), the driver sections are designed to accept input
supply rails (VIN) as high as 14V.
The demo board design regulates to an output voltage of 1.2V at 3.5A with a switching frequency of
1MHz. Note, the demo board is optimized for a 1MHz, 14V input voltage compensation design, if another
switching frequency and input voltage is desired, please consult the LM2743 data sheet for control loop
compensation procedures. For additional design modifications refer to the Design Consideration section of
the LM2743 Low Voltage N-Channel MOSFET Synchronous Buck Regulator Controller Data Sheet
(SNVS276). The PCB is designed on two layers with 1oz. copper on a 62mil FR4 laminate.
2
Additional Footprints
A Schottky diode footprint (D1) is available in parallel to the low side MOSFET. This component can
improve efficiency, due to the lower forward drop than the low side MOSFET body diode conducting
during the anti-shoot through period. Select a Schottky diode that maintains a forward drop around 0.4 to
0.6V at the maximum load current (consult the I-V curve). In addition select the reverse breakdown
voltage to have sufficient margin above the maximum input voltage.
Footprint C13 is available for a multilayer ceramic capacitor (MLCC) connected as close as possible to the
source of the low side MOSFET and drain of the high side MOSFET. This will provide low supply
impedance to the high speed switch currents, thus minimizing the input supply noise. For example; a
MLCC is used (C13) in combination with aluminum electrolytic input filter capacitors, placed in designators
C12 and C14, because MLCC have lower impedance than electrolytics. If MLCCs are used in designators
C12 and C14 then component C13 is not necessary.
3
Typical Application Circuit
The typical application circuit in Figure 1 provides the component designators used on the demo board.
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1
Typical Application Circuit
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VC
D2
C
R11
R8
R1
J1
C5
C12
HG
VCC
SD
BOOT
PWGD
C14
Q1
VOUT
L1
R4
ISEN
LM2743
FREQ
R2
C7
VIN
C10
LG
SS/TRACK
PGND
SGND
PGND
+
Q2
C16
FB
EAO
C9
R3
R5
C11
R6
C8
R7
Figure 1. Typical Application
2
AN —1356 LM2743 Evaluation Board
SNVA102A – October 2005 – Revised April 2013
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Performance Characteristics
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4
Performance Characteristics
4.1
Switch Node Voltage and Output Ripple Voltage
Figure 2. VIN = VCC = 3.3V,
VOUT = 1.2V,
ILOAD = 0A, fSW = 1MHz.
20 MHz Bandwidth Limit
Figure 3. VIN = VCC = 3.3V,
VOUT = 1.2V,
ILOAD = 3.5A, fSW = 1MHz.
20 MHz Bandwidth Limit
Figure 4. VIN = 14V, VCC = 5V,
VOUT = 1.2V, ILOAD = 0A, fSW = 1MHz.
20 MHz Bandwidth Limit
Figure 5. VIN = 14V, VCC = 5V,
VOUT = 1.2V, ILOAD = 3.5A, fSW = 1MHz.
20 MHz Bandwidth Limit
SNVA102A – October 2005 – Revised April 2013
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3
Performance Characteristics
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Table 1. Bill of Materials
Designator
Function
Part Description
Part Number
U1
Controller
IC LM2743 TSSOP14
Texas Instruments
C5
VCC Decoupling
Cer Cap 1µF 25V 10% 0805
Murata GRM216R61E105KA12B
C7
Soft Start Cap
Cer Cap 12nF 25V 10% 0805
Vishay VJ0805Y123KXX
C8
Comp Cap
Cer Cap 1.5nF 25V 10% 0805
Vishay VJ0805Y152KXX
C9
Comp Cap
Cer Cap 18pF 25V 10% 0805
Vishay VJ0805A180KAA
C10
Cboot
Cer Cap 0.1µF 25V 10% 0805
Vishay VJ0805Y104KXX
C11
Comp Cap
Cer Cap 1.8nF 25V 10% 0805
Vishay VJ0805Y182KXX
C12
Input Filter Cap
Cer Cap 10uF 25V 10% 1210
AVX 12103D106MAT
C14
Input Filter Cap
Cer Cap 10uF 25V 10% 1210
AVX 12103D106MAT
C15
Output Filter Cap
470µF, 6.3V, 10mΩ ESR POScap
Sanyo 6TPD470
R1
Filter Resistor
Res 10Ω .25W 0805
Vishay CRCW08051000F
R2
Frequency Adjust Res
Res 24.9KΩ .25W 0805
Vishay CRCW08052492F
R3
Comp Res
Res 17.4KΩ .25W 0805
Vishay CRCW08051742F
R4
Current Limit Res
Res 3.16KΩ .25W 0805
Vishay CRCW08053161F
R5
Comp Res
Res 2.94KΩ .25W 0805
Vishay CRCW08052941F
R6
Res Divider, upper
Res 10.0KΩ .25W 0805
Vishay CRCW08051002F
R7
Res Divider, lower
Res 10.0KΩ .25W 0805
Vishay CRCW08051002F
R8
PWGD Pull-Up
Res 100KΩ .25W 0805
Vishay CRCW08051003F
R11
Shut Down Pull-Up
Res 100KΩ .25W 0805
Vishay CRCW080561003F
D2
Bootstrap Diode
Schottky Diode, SOD-123
MBR0530LTI
L1
Output Filter Inductor
Inductor 1µH, 5.3Arms, 10.2mΩ
Cooper DR73-1R0
Q1-Q2
Top and Bottom FETs
Dual N-MOSFET, VDS = 20V, 24mΩ @ 2.5V
Vishay 9926BDY
VC
D2
C
R1
R11
R8
C13
VCC
J1
C5
HG
SD
BOOT
PWGD
FREQ
R2
C7
VIN
C10
C12
C14
Q1
VOUT
L1
R4
ISEN
LM2743
LG
SS/TRACK
PGND
SGND
PGND
D1
Q2
C15
+
+
C16
FB
EAO
C9
R3
R5
C11
R6
C8
R7
Figure 6. Complete Demo Board Schematic
4
AN —1356 LM2743 Evaluation Board
SNVA102A – October 2005 – Revised April 2013
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PCB Layout Diagram(s)
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5
PCB Layout Diagram(s)
Figure 7. Top Layer and Top Overlay
Figure 8. Bottom Layer
SNVA102A – October 2005 – Revised April 2013
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