User's Guide
SNVA101A – December 2004 – Revised April 2013
AN-1352 LM5010 Evaluation Board
1
Introduction
The LM5010EVAL evaluation board provides the design engineer with a fully functional buck regulator,
employing the constant on-time (COT) operating principle. This evaluation board provides a 10V output
from an input range of 12V - 75V. The circuit provides load currents > 1A, with the current limit set at
≊1.3A.
The board’s specification are:
• Input Voltage: 12V to 75V
• Output Voltage: 10V, ±3%
• Maximum Continuous Output current: 1.0A
• Current Limit: 1.3A
• Measured Efficiency: 93% (VIN = 12V, IOUT = 500 mA)
• Switching Frequency: ≊480 kHz
• Size: 1.1 in. x 1.875 in. x 0.47 in
LM5010 EVALUATION BD
NATIONAL
SEMICONDUCTOR
55101 2308-001 REV B
D1
C2002
OUT2
J3
IN
J1
OUT1
C6
GND
R2
C3
R3
C5
L1
C4
GND
U1
R5
R4
C7
R1
C1
C2
Figure 1. Evaluation Board - Top Side
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SNVA101A – December 2004 – Revised April 2013
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AN-1352 LM5010 Evaluation Board
1
Theory of Operation
2
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Theory of Operation
Refer to the board’s schematic in Figure 4, which contains a simplified block diagram of the LM5010.
When the circuit is in regulation, the buck switch is on each cycle for a time determined by R1 and VIN
according to the equation:
1.18 x 10-10 x (R1 + 1.4k)
tON =
+ 67 ns
VIN - 1.4V
(1)
The on-time in this evaluation board will range from ≊1750 ns at VIN = 12V, to ≊310 ns at VIN = 75V. At the
end of the on-time, the feedback voltage at FB is above 2.5V, and the Minimum Off-Timer ensures the
buck switch is off for at least 265 ns. In normal operation, the off-time is longer. During the off-time, the
output capacitor (C7) discharges, and when the output voltage falls so that the voltage at FB is below
2.5V, the comparator output switches to initiate a new on-time. As required by the datasheet, this circuit
provides a minimum of 25mVp-p ripple at the FB pin. Refer to the LM5010 data sheet for a more detailed
block diagram, and a complete description of the various functional blocks.
3
Board Layout and Probing
The pictorial in Figure 1 shows the placement of the circuit components. The following should be kept in
mind when the board is powered:
1) When operating at high input voltage and/or high load current, forced air flow IS NECESSARY.
2) The LM5010, and the diode D1 will be hot to the touch when operating at high input voltage and/or high
load current.
3) Use CAUTION when probing the circuit at high input voltages. 75 volts is enough to produce shocks
and sparks.
4) At maximum load current (1A), the wire size and length used to connect the load becomes important.
Ensure there is not a significant drop in the wires.
4
Board Connection/Start-up
The input connections are made to the J1 connector. The load is normally connected to the OUT1 and
GND terminals of the J3 connector. Ensure the wires are adequately sized for the intended load current.
Before start-up a voltmeter should be connected to the input terminals, and to the output terminals. The
load current should be monitored with an ammeter or a current probe. It is recommended that the input
voltage be increased gradually to 8V, at which time the output voltage will be approximately 7V. If that
indicates correctly, then increase the input voltage to the minimum operating value of 12V, and proceed
with evaluating the circuit.
5
Low Ripple Output
The ripple voltage at OUT1 will range from ≊ 120 mVp-p (at VIN = 12V) to ≊ 650 mVp-p (at VIN = 75V). If a
low ripple output is desired, connect the load to OUT2. The ripple at this output varies from ≊ 10mVp-p to
≊ 60 mVp-p over the input voltage range. However, the load regulation is not as good at OUT2 as it is at
OUT1 due to the presence of R4.
6
Increased Current Limit
The evaluation board current limit activates at a load current of ≊1.3A. If it is desired to increase the
current limit for a particular application, R5 must be added to the board. Refer to the data sheet to
determine the appropriate value for this resistor.
2
AN-1352 LM5010 Evaluation Board
SNVA101A – December 2004 – Revised April 2013
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Increased Current Limit
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100
VIN = 12V
EFFICIENCY (%)
90
_
VIN = 48V
80
_
VIN = 75V
70
_
60
0
200
400
600
800
1000
LOAD CURRENT (mA)
Figure 2. Efficiency vs Load Current
100
EFFICIENCY (%)
90
_
80
_
70
Load Current = 500 mA
_
60
0
_
20
_
40
_
60
_
80
VIN (V)
Figure 3. Efficiency vs VIN
SNVA101A – December 2004 – Revised April 2013
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AN-1352 LM5010 Evaluation Board
3
Increased Current Limit
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12 - 75V
Input
VIN
C1
2.2 PF
C2
2.2 PF
R1
150k
VCC
LM5010
13
12
C3
0.1PF
Minimum
Off
Timer
On
Timer
BST
3
C6
RON/SD
11
C5
0.022 PF
0.022 PF
L1 47 PH
SW
2
Logic
SS
10
C4
0.1 PF
10V
R2
3.0k
4
FB
9
VOUT1
D1
ISEN
2.5V
R5
R4
1.5
VOUT2
SGND
R3
1.0k
5
6
RTN
C7
22 PF
GND
Figure 4. Board Schematic
Table 1. Bill of Materials
4
Item
Description
Mfg. Part Number
Package
Value
C1, 2
Ceramic Capacitor
TDK C4532X7R2A225M
1812
2.2 µF, 100V
C3
Ceramic Capacitor
TDK C2012X7R2A104M
0805
0.1 µF, 100V
C4
Ceramic Capacitor
TDK C2012X7R1C104M
0805
0.1 µF, 16V
C5, 6
Ceramic Capacitor
TDK C2012X7R1C223M
0805
0.022 µF, 16V
C7
Ceramic Capacitor
TDK C4532X7R1E226M
1812
22 µF, 25V
D1
Ultra Fast Diode
Central Semi CUD6-02C
DPAK
200V, 6A, 35 ns
L1
Power Inductor
TDK SLF12575T-470M2R7
12.5 mm x 12.5 mm
47 µH, 3A
R1
Resistor
CRCW08051503F
0805
150 kΩ
R2
Resistor
CRCW08053001F
0805
3.00 kΩ
R3
Resistor
CRCW08051001F
0805
1.00 kΩ
R4
Resistor
CRCW08051R50F
0805
1.5Ω
R5
Resistor
See data sheet
0805
U1
Switching Regulator
Texas Instruments LM5010
HTSSOP - 14
AN-1352 LM5010 Evaluation Board
SNVA101A – December 2004 – Revised April 2013
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PCB Layout
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7
PCB Layout
SNVA101A – December 2004 – Revised April 2013
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AN-1352 LM5010 Evaluation Board
5
PCB Layout
6
AN-1352 LM5010 Evaluation Board
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SNVA101A – December 2004 – Revised April 2013
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Copyright © 2004–2013, Texas Instruments Incorporated
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