User's Guide
SNVA404B – July 2009 – Revised May 2013
AN-1986 LM3429 Boost Evaluation Board
1
Introduction
This evaluation board showcases the LM3429 NFET controller used with a boost current regulator. It is
designed to drive 9 to 12 LEDs at a maximum average LED current of 1A from a DC input voltage of 10 to
26V.
The evaluation board showcases most features of the LM3429 including PWM dimming, overvoltage
protection and input under-voltage lockout. It also has a right angle connector (J7) which can mate with an
external LED load board allowing for the LEDs to be mounted close to the driver. Alternatively, the LED+
and LED- banana jacks can be used to connect the LED load.
The boost circuit can be easily redesigned for different specifications by changing only a few components
(see Alternate Designs ). Note that design modifications can change the system efficiency for better or
worse. See the LM3429 LM3429Q1 N-Channel Controller for Constant Current LED Drivers (SNVS616)
data sheet for a comprehensive explanation of the device and application information.
100
EFFICIENCY (%)
95
90
85
80
10
15
20
25
30
VIN (V)
Figure 1. Efficiency with 9 Series LEDS AT 1A
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1
Schematic
2
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Schematic
TP7
VIN
TP1
L1
J1
TP10
J2
D1
C2, C3,
C16, C18
R10
GND
U1
C1
R3
1
VIN
VIN
LM3429
HSN
14
R7
13
R8
R9
C12
R2
C8
2
HSP
COMP
R20
3
CSH
IS
LED+
12
J4
R1
4
RCT
VCC
11
C7
6
R13
AGND
GATE
OVP
PGND
14
2
13
3
12
4
11
5
10
6
9
7
8
TP3
C9
5
1
10
9
C4, C6,
C17, C19
TP2
Q1
R6
R18
DAP
R4
7
nDIM
NC
8
J5
TP11
R5
J7
LED-
Q3
PWM
R11
R12
TP12
Figure 2. Board Schematic
2
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Pin Descriptions
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3
Pin Descriptions
Pin
4
Name
Description
Application Information
1
VIN
Input Voltage
Bypass with 100 nF capacitor to AGND as close to the device as
possible in the circuit board layout.
2
COMP
Compensation
Connect a capacitor to AGND.
3
CSH
Current Sense High
4
RCT
Resistor Capacitor Timing
5
AGND
Analog Ground
6
OVP
Over-Voltage Protection
7
nDIM
Not DIM input
Connect a PWM signal for dimming as detailed in the PWM
Dimming section and/or a resistor divider from VIN to program
input under-voltage lockout (UVLO). Turn-on threshold is 1.24V
and hysteresis for turn-off is provided by 20 µA current source.
8
NC
No Connection
Leave open.
9
PGND
Power Ground
Connect to AGND through the DAP copper circuit board pad to
provide proper ground return for GATE.
10
GATE
Gate Drive Output
11
VCC
Internal Regulator Output
12
IS
Main Switch Current Sense
13
HSP
High-Side LED Current Sense
Positive
Connect through a series resistor to the positive side of the LED
current sense resistor.
14
HSN
High-Side LED Current Sense
Negative
Connect through a series resistor to the negative side of the
LED current sense resistor.
DAP
(15)
DAP
Thermal pad on bottom of IC
Connect a resistor to AGND to set the signal current. For analog
dimming, connect a controlled current source or a potentiometer
to AGND as detailed in the Analog Dimming section.
Connect a resistor from the switch node and a capacitor to
AGND to set the switching frequency.
Connect to PGND through the DAP copper circuit board pad to
provide proper ground return for CSH, COMP, and RCT.
Connect to a resistor divider from VO to program output overvoltage lockout (OVLO). Turn-off threshold is 1.24V and
hysteresis for turn-on is provided by 20 µA current source.
Connect to the gate of the external NFET.
Bypass with a 2.2 µF–3.3 µF, ceramic capacitor to PGND.
Connect to the drain of the main N-channel MosFET switch for
RDS-ON sensing or to a sense resistor installed in the source of
the same device.
Star ground, connecting AGND and PGND.
Bill of Materials
Qty
Manufacturer
Part Number
2
C1, C4
Part ID
0.1 µF X7R 10% 100V
Part Value
TDK
C2012X7R2A104K
4
C2, C3, C16, C18
4.7 µF X7R 10% 100V
MURATA
GRM55ER72A475KA01L
3
C6, C17, C19
2.2 µF X7R 10% 100V
TDK
C4532X7R2A225K
1
C7
1000 pF COG/NPO 5% 50V
MURATA
GRM2165C1H102JA01D
1
C8
1 µF X7R 10% 16V
MURATA
GRM21BR71C105KA01L
1
C9
2.2 µF X7R 10% 16V
MURATA
GRM21BR71C225KA12L
1
C12
0.1 µF X7R 10% 25V
MURATA
GRM21BR71E104KA01L
1
D1
Schottky 100V 12A
VISHAY
12CWQ10FNPBF
4
J1, J2, J4, J5
banana jack
1
J7
2 x 7 shrouded header
1
L1
33 µH 20% 6.3A
1
Q1
NMOS 100V 40A
1
Q3
NMOS 60V 260 mA
1
R1
1
2
KEYSTONE
575-8
SAMTEC
TSSH-107-01-SDRA
COILCRAFT
MSS1278-333MLB
VISHAY
SUD40N10-25
ON-SEMI
2N7002ET1G
12.4 kΩ 1%
VISHAY
CRCW080512k4FKEA
R2
0Ω 1%
VISHAY
CRCW08050000Z0EA
R3, R20
10Ω 1%
VISHAY
CRCW080510R0FKEA
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3
Bill of Materials
4
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1
R4
16.9 kΩ 1%
VISHAY
CRCW080516k9FKEA
1
R5
1.43 kΩ 1%
VISHAY
CRCW08051k43FKEA
1
R6
0.04Ω 1% 1W
VISHAY
WSL2512R0400FEA
2
R7, R8
1.0 kΩ 1%
VISHAY
CRCW08051k00FKEA
1
R9
0.1Ω 1% 1W
VISHAY
WSL2512R1000FEA
1
R10
35.7 kΩ 1%
VISHAY
CRCW080535k7FKEA
1
R11
15.8 kΩ 1%
VISHAY
CRCW080515k8FKEA
2
R12, R13
10.0 kΩ 1%
VISHAY
CRCW080510k0FKEA
1
R18
750 kΩ 1%
7
TP1, TP2, TP3, TP7,
TP10, TP11, TP12
turret
1
U1
Buck-boost controller
VISHAY
CRCW0805750kFKEA
KEYSTONE
1502-2
TI
LM3429
AN-1986 LM3429 Boost Evaluation Board
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PCB Layout
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5
PCB Layout
Figure 3. Top Layer
Figure 4. Bottom Layer
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Design Procedure
6
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Design Procedure
Refer to LM3429 LM3429Q1 N-Channel Controller for Constant Current LED Drivers (SNVS616) data
sheet for design considerations.
6.1
Specifications
N=9
VLED = 3.5V
rLED = 325 mΩ
VIN = 24V
VIN-MIN = 10V; VIN-MAX = 27V
fSW = 700 kHz
VSNS = 100 mV
ILED = 1A
ΔiL-PP = 250 mA
ΔiLED-PP = 17 mA
ΔvIN-PP = 100 mV
ILIM = 6A
VTURN-ON = 10V; VHYS = 3V
VTURN-OFF = 60V; VHYSO = 15V
6.2
Operating Point
Solve for VO and rD:
VO = N x VLED = 9 x 3.5V = 31.5 V
(1)
rD = N x rLED = 9 x 325 m: = 2.925 :
(2)
Solve for D, D', DMAX, and DMIN:
D=
VO - VIN 31.5V - 24V
=
= 0. 238
VO
31.5 V
D' = 1 - D = 1 - 0. 238 = 0. 762
6.3
(3)
(4)
VO - VIN - MAX 31.5V - 26V
=
= 0.175
DMIN =
31.5 V
VO
(5)
VO - VIN - MIN 31.5V - 10V
=
= 0.683
DMAX =
31.5 V
VO
(6)
Switching Frequency
Assume C7 = 1 nF and solve for R10:
R10 =
25
25
=
= 35.7 k:
fSW x C7 700 kHz x 1 nF
(7)
The closest standard resistor is actually 35.7 kΩ therefore the fSW is:
fSW =
25
25
=
= 700 kHz
R10 x C7 35.7 k: x 1 nF
(8)
The chosen components from step 2 are:
C7 = 1 nF
R10 = 35.7 k:
6
(9)
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Design Procedure
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6.4
Average LED Current
Solve for R9:
VSNS 100 mV
=
= 0.1:
ILED
1A
R9 =
(10)
Assume R1 = 12.4 kΩ and solve for R8:
ILED x R1 x R9 1A x 12.4 k: x 0.1:
=
= 1.0 k:
1.24V
1.24V
R8 =
(11)
The closest standard resistor for R9 is 0.1Ω and the closest for R8 (and R7) is actually 1 kΩ therefore ILED
is:
ILED =
1.24V x R8 1.24V x 1.0 k:
=
= 1.0A
0.1: x 12.4 k:
R9 x R1
(12)
The chosen components from step 3 are:
R9 = 0.1:
R1 = 12.4 k:
R8 = R7 = 1 k :
6.5
(13)
Inductor Ripple Current
Solve for L1:
L1 =
VIN x D
24V x 0. 238
=
= 32.6 PH
'iL- PP x fSW 250 mA x 700 kHz
(14)
The closest standard inductor is 33 µH therefore the actual ΔiL-PP is:
'iL- PP =
VIN x D
24V x 0. 238
= 247 mA
=
L1 x fSW 33 PH x 700 kHz
(15)
Determine minimum allowable RMS current rating:
2
IL - RMS =
ILED
1 x §¨ 'iL - PP x Dc·¸
x 1+
12 ¨© ILED ¸¹
Dc
2
1 x §247 mA x 0.762·
1A
x 1+
¸¸
12 ¨¨©
1A
0. 762
¹
IL - RMS = 1.31A
IL - RMS =
(16)
The chosen component from step 4 is:
L1 = 33 PH
6.6
(17)
Output Capacitance
Solve for CO:
CO =
CO =
ILED x D
rD x 'iLED- PP x fSW
1A x 0. 238
= 6.84 PF
2.925 : x 17 mA x 7 00 kHz
(18)
A total value of 6.6 µF (using 3 2.2 µF X7R ceramic capacitors) is chosen therefore the actual ΔiLED-PP is:
'iLED- PP =
ILED x D
rD x CO x fSW
'iLED- PP =
1A x 0. 238
= 17.6 mA
2.925 : x 6.6 PF x 7 00 kHz
(19)
Determine minimum allowable RMS current rating:
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Design Procedure
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ICO- RMS = ILED x
DMAX
0.683
= 1.47A
= 1A x
1- DMAX
1- 0.683
(20)
The chosen components from step 5 are:
C6 = C17 = C19 = 2.2 PF
6.7
(21)
Peak Current Limit
Solve for R6:
R6 =
245 mV 245 mV
=
= 0.041 :
ILIM
6A
(22)
The closest standard resistor is 0.04 Ω therefore ILIM is:
ILIM =
245 mV 245 mV
=
= 6.1A
0.04 :
R6
(23)
The chosen component from step 6 is:
R6 = 0.04:
6.8
(24)
Loop Compensation
ωP1 is approximated:
ZP1 =
rad
2
2
=
= 104 k
sec
rD x CO 2.925: x 6.6 PF
(25)
ωZ1 is approximated:
ZZ1 =
rD x Dc2 2.925 : x 0.7622
rad
=
= 52k
L1
33PH
sec
(26)
TU0 is approximated:
TU0 =
Dc x 310V 0.762 x 310V
=
= 5900
ILED x R LIM 1A x 0.04:
(27)
To ensure stability, calculate ωP2:
ZP2 =
rad
52k
min(ZP1, ZZ1)
ZZ1
sec
rad
=
=
= 1. 76
5 x 5900 5 x 5900
5 x TU0
sec
(28)
Solve for C8:
C8 =
1
1
=
= 0.11 PF
ZP2 x 5e6: 1.76 rad x 5e6:
sec
(29)
Since PWM dimming can be evaluated with this board, a much larger compensation capacitor C8 = 1.0 µF
is chosen.
To attenuate switching noise, calculate ωP3:
ZP3 = max(ZP1, ZZ1) x 10 = ZP1 x10
ZP3 = 104 k
rad
rad
x 10 = 1.04 M
sec
sec
(30)
Assume R20 = 10Ω and solve for C12:
C12 =
1
=
10: x ZP3
1
10: x 1.04M
rad
sec
= 0.097 PF
(31)
The chosen components from step 7 are:
8
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C8 = 1.0 PF
R20 = 10:
C12 = 0.1 PF
6.9
(32)
Input Capacitance
Solve for the minimum CIN:
CIN =
'iL - PP
250 mA
=
= 0.45 PF
8 x 'vIN- PP x fSW 8 x 100 mV x 700 kHz
(33)
To minimize power supply interaction a much larger capacitance of approximately 20 µF is used, therefore
the actual ΔvIN-PP is much lower. Since high voltage ceramic capacitor selection is limited, four 4.7 µF X7R
capacitors are chosen.
Determine minimum allowable RMS current rating:
IIN - RMS =
'iL - PP
12
=
250 mA
12
= 72 mA
(34)
The chosen components from step 8 are:
C2 = C3 = C16 = C18 = 4.7 PF
(35)
6.10 NFET
Determine minimum Q1 voltage rating and current rating:
VT - MAX = VO = 31.5V
IT- MAX =
(36)
0. 683
x 1A = 2.2A
1- 0.683
(37)
A 100V NFET is chosen with a current rating of 40A due to the low RDS-ON = 50 mΩ. Determine IT-RMS and
PT:
IT - RMS =
ILED
1A
x D=
x 0.238 = 640 mA
0. 762
Dc
(38)
2
PT = IT- RMS x RDSON = 640 mA2 x 50 m: = 20 mW
(39)
The chosen component from step 9 is:
Q1 o 40A, 100V, DPAK
(40)
6.11 Diode
Determine minimum D1 voltage rating and current rating:
VRD- MAX = VO = 31.5V
(41)
ID - MAX = ILED = 1A
(42)
A 100V diode is chosen with a current rating of 12A and VD = 600 mV. Determine PD:
PD = ID x VFD = 1A x 600 mV = 600 mW
(43)
The chosen component from step 10 is:
D1 o 12A, 100V, DPAK
(44)
6.12 Input UVLO
Since PWM dimming will be evaluated a three resistor network will be used. Assume R13 = 10 kΩ and
solve for R5:
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Design Procedure
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R5 =
1.24V x R13
1.24V x 10 k:
=
= 1.43 k:
VTURN - ON - 1.24V
10V -1.24V
(45)
The closest standard resistor is 1.43 kΩ therefore VTURN-ON is:
VTURN - ON =
1.24V x ( R5 + R13)
R5
VTURN- ON =
1.24V x (1.43 k: +10 k:)
= 9.91V
1.43 k :
(46)
Solve for R4:
R4 =
R4 =
R5 x (VHYS - 20 PA x R13)
20 PA x (R5 + R13)
1.43 k: x (2.9V - 20 PA x 10 k:)
= 16.9 k:
20 PA x (1.43 k: + 10 k:)
(47)
The closest standard resistor is 16.9 kΩ making VHYS:
VHYS =
VHYS =
20 PA x R4 x (R5 + R13)
+ 20 PA x RUV2
R5
20 PA x 16.9 k: x (1.43 k: + 10 k:)
1.43 k:
+ 20 PA x 10 k: = 2.9V
(48)
The chosen components from step 11 are:
R5 = 1.43 k:
R13 = 10 k:
R4 = 16.9 k:
(49)
6.13 Output OVLO
Solve for R18:
R18 =
VHYSO
15V
=
= 750 k:
20 P A 20 P A
(50)
The closest standard resistor is 750 kΩ therefore VHYSO is:
VHYSO = R18 x 20 PA = 750 k: x 20 PA = 15V
(51)
Solve for R11:
R11 =
1.24V x 750 k:
1.24V x R18
=
= 15.8 k:
VTURN - OFF - 1.24V
60V -1.24V
(52)
The closest standard resistor is 15.8 kΩ making VTURN-OFF:
VTURN - OFF =
1.24V x ( R11 + R18)
R11
VTURN- OFF =
1.24V x (15.8 k: + 750 k:)
= 40V
15.8 k:
(53)
The chosen components from step 12 are:
R11 = 15.8 k:
R18 = 750 k:
10
(54)
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Typical Waveforms
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7
Typical Waveforms
TA = +25°C, VIN = 24V and VO = 31.5V.
0.0
0.0
40
10
20
0
VDIM (V)
VSW (V)
1.0
ILED
VSW
ILED (A)
0.5
ILED (A)
1.0
ILED
-1.0
5
0
VDIM
2 Ps/DIV
4 ms/DIV
Figure 5. Standard Operation
TP1 Switch Node Voltage (VSW)
LED Current (ILED)
8
Figure 6. 200Hz 50% PWM Dimming
TP11 Dim Voltage (VDIM)
LED Current (ILED)
Alternate Designs
Alternate designs with the LM3429 evaluation board are possible with very few changes to the existing
hardware. The evaluation board FETs and diodes are already rated higher than necessary for design
flexibility. The input UVLO, output OVP, input and output capacitance can remain the same for the designs
shown below. These alternate designs can be evaluated by changing only R9, R10, and L1.
Table 1 gives the main specifications for four different designs and the corresponding values for R9, R10,
and L1. PWM dimming can be evaluated with any of these designs.
Table 1. Alternate Design Specifications
Specification /
Component
Design 1
Design 2
Design 3
Design 4
VIN
10V
15V
20V
25V
VO
14V
21V
28V
35V
fSW
600kHz
700kHz
500kHz
700kHz
ILED
2A
500mA
2.5A
1.25A
R9
0.05Ω
0.2Ω
0.04Ω
0.08Ω
R10
41.2 kΩ
35.7 kΩ
49.9 kΩ
35.7 kΩ
L1
22µH
68µH
15µH
33µH
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