User's Guide
SNVA612B–January 2012–Revised April 2013
AN-2200 LM5017 Evaluation Board
1 Introduction
The LM5017 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 10 V output
over an input range of 12.5 V to 100 V.
The board’s specifications are:
• Input Range: 12.5 V to 95 V, transients up to 100 V (absolute maximum)
• Output Voltage: 10 V
• Output Current: 600 mA
• Nominal Switching Frequency ~ 200 kHz
• Measured Efficiency: 92.4% at 400 mA and VIN = 24 V
• Board size: 2.95 in. x 1.8 in.
Figure 1. Evaluation Board (Top View)
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1
SNVA612B–January 2012–Revised April 2013 AN-2200 LM5017 Evaluation Board
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+
+
+
VIN BST
RON
RTN
SW
VCC
FB
VIN
VOUT
R2
R7
R3
C9
C1
C4
R1
R5 L1
UVLO
C7
LM5017
12V-100V
1
2
3
4
5
6
8
7
(TP4)
+
C4
2.2 F 0.47 F127 NŸ
14 NŸ
499 NŸ
GND
(TP1)
(TP2)
UVLO/SD
U1
R6
(TP3)
(TP5)
GND
R4 C6
C8
+
D2
C2
R8
EXP
0Ÿ
1 NŸ
6.98 NŸ
22 F
0Ÿ
220 H
0.01 F
1 F
3300 pF
0.1 F
46.4 NŸ
(TP6)
SW
R5
VIN (UVLO,rising) = 1.225V x R7+1¹
·
©
§
VIN(HYS) =IHYSR5
TON =
VIN
10-10 x R3
Theory of Operation
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2 Theory of Operation
When the circuit is in regulation, the buck switch is turned on each cycle for a time determined by R3 and
VIN according to Equation 1:
(1)
The on-time of this evaluation board ranges from 5.56 µs at VIN = 12 V to 702 ns at VIN = 95 V. The on-
time varies inversely with input voltage. At the end of each on-time, the buck switch is off for at least 144
ns. In normal operation, the off-time is much longer. During the off-time, the load current is supplied by the
output capacitor (C9). When the output voltage falls sufficiently that the voltage at FB is below 1.225 V,
the regulation comparator initiates a new on-time period. For stable, fixed frequency operation, a minimum
of 25 mV of ripple is required at FB to switch the regulation comparator. For a more detailed block
diagram and a complete description of the various functional blocks, see the LM5017 100V, 600mA
Constant On-Time Synchronous Buck Regulator Data Sheet (SNVS783).
3 UVLO
The UVLO resistors (R5, R7) are selected using Equation 2:
(2)
and Equation 3:
(3)
On this evaluation board, R5 = 127 kΩand R7 = 14.0 kΩ, resulting in UVLO rising threshold at VIN = 12 V
and a hysteresis of 2.5 V.
Figure 2 shows the evaluation board schematic.
Figure 2. Complete Evaluation Board Schematic for LM5017-Based Buck Converter
4 Board Connection and Start-up
The input connections are made to the TP1 (VIN) and TP2 (GND) terminals. The load is connected to the
TP3 (VOUT) AND TP5 (GND) terminals. Ensure the wires are adequately sized for the intended load
current. Before start-up, a voltmeter should be connected to the input and 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 12 V, at which time the output voltage should be 10 V. If the output voltage is
correct, increase the input voltage as desired and proceed with evaluating the circuit. DO NOT EXCEED
100 V AT VIN.
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Board Connection and Start-up
Table 1. Bill of Materials (BOM)
Item Description Mfg. Part Number Package Value
U1 Sync Switching Texas Instruments, LM5017 SO PowerPAD-8 100 V, 0.6A
Regulator
Inductor Wurth, 7447714221 10 mm x 10 mm 220 µH, 1.2A
Alternate Inductor Bourns, SRR1260–221k 12.5 mm x 12.5 220 µH, 1.38A
L1 mm
Alternate Inductor Coilcraft, MSS1246–224K 12.3 mm x 220 µH, 1.4A
12.3 mm
D2 Diode Central Semi, CMMSH1–40 SOD-123F 40 V, 1A
Alternate Diode NXP, BAS40H, 115 SOD123F 40 V, 120 mA
C1 Ceramic Capacitor Murata, GRM188R71C103KA01D 0603 0.01 µF, 16V,
X7R
C2 NA
C4 Ceramic Capacitor Murata, GRM32ER72A225KA35L 1210 2.2 µF, 100 V,
X7R
C5 Ceramic Capacitor Murata, GRM21BR72A474KA73L 0805 0.47 µF, 100 V,
X7R
C6 Ceramic Capacitor TDK, C1608X7R1H332K 0603 3300 pF, 50 V,
X7R
C7 Ceramic Capacitor TDK, C2012X7R1C105K 0805 1 µF, 16 V, X7R
C8 Ceramic Capacitor Murata, GRM188R71E104KA01D 0603 0.1 uF, 25 V, X7R
C9 Ceramic Capacitor Murata, GRM32ER71E226KE15L 1210 22 uF, 25 V, X7R
R1 Resistor Vishay–Dale, CRCW08056K98FKEA 0805 6.98k Ω, 1%
R2 Resistor Panasonic, ERJ-6GEY0R00V 0805 0 Ω
R3 Resistor Panasonic, ERJ-6ENF4993V 0805 499k Ω, 1%
R4 Resistor Panasonic, ERJ-3EKF4642V 0603 46.4k Ω, 1%
R5 Resistor Vishay-Dale, CRCW0805127KFKEA 0805 127k Ω, 1%
R6 Resistor Vishay-Dale, CRCW08051K00FKEA 0805 1.0k Ω, 1%
R7 Resistor Vishay-Dale, CRCW080514K0FKEA 0805 14.0k Ω, 1%
R8 Resistor Yageo, RC1206JR-070RL 1206 0 Ω
3
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40 mV
C6 = 3300 pF
R4 x C6 (VIN(MIN) ± VOUT)TON
C8 = 100 nF
<
ûIL
40 mV
C8 5
R2
>gSW (R1 || R6)
>
VREF
40 mV
R2 > ûIL(MIN)
VOUT
x
GND
Rr
Cac
To FB
L1
COUT
RFB2
RFB1
VOUT
Cr
GND
To FB
L1
COUT
RFB2
RFB1
VOUT
RC
GND
To FB
L1
COUT
RFB2
RFB1
VOUT
RC
Cac
Ripple Configuration
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5 Ripple Configuration
The LM5017 is a COT buck and requires adequate ripple at feedback (FB) node. Three commonly used
ripple generation methods are shown in Table 2.
LM5017 evaluation board has been supplied with minimum ripple configuration (Type 3), but can be
configured to Type 1 or Type 2 with modifications as suggested in Table 2.
Table 2. Ripple Configuration
Type 1 Type 2 Type 3
Lowest Cost Configuration Reduced Ripple Configuration Minimum Ripple Configuration
R4, C6, C8 open. Select R2: R4 open, C6 = 0 Ω. Select R2 and C8: R2 = 0 Ω. Select R4, C6, and C8:
(4)
(5) (6)
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Performance Curves
6 Performance Curves
Figure 3. Efficiency vs Load Current Figure 4. Frequency vs Input Voltage
Figure 5. Typical Switching Waveform (VIN = 48 V, Iout = 200 mA)
5
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