Texas Instruments LM3464 Application Note
LM3464
Application Note 2071 LM3464A 4 Channel LED Driver Evaluation Board
Literature Number: SNVA449C
LM3464A 4 Channel LED Driver Evaluation Board AN-2071
LM3464A 4 Channel LED
Driver Evaluation Board
Introduction
This evaluation board demonstrates the high power efficiency
and outstanding output current accuracy of the LM3464A typical application circuit. With four LED strings connected, the
total output power is about 50W. The schematic, bill of material and PCB layout drawing of the LM3464A evaluation board
are provided in this document. This evaluation board can be
adapted to different types of power supply with changes of a
few components. The PCB of this evaluation board is pin to
pin compatible to both LM3464 and LM3464A with 80V and
95V maximum input voltage respectively. The information being presented in this document are also applicable to both the
LM3464 and LM3464A.
The LM3464A is a 4 channel linear LED driver which combined the advantages of high power efficiency of switching
regulators and low current ripple of linear current regulators.
With the incorporation of the proprietary Dynamic Headroom
Control (DHC) technology, the LM3464A optimizes system
efficiency automatically while providing outstanding output
stability and accuracy. Each LED current regulators of this
board consists of an external MOSFET and a control circuit
inside the LM3464A to provide the best flexibility to fulfill the
needs of different applications. The LM3464A includes a builtin Low Drop-Out (LDO) voltage regulator which accepts an
input voltage up to 95V (LM3464A) to provide power and voltage references to internal circuits, allowing the LM3464A to
adapt to difference source voltages easily. The integrated
thermal foldback control circuit protects the LED Strings from
damages due to over-temperature. This eventually secures
the lifetime of the entire lighting system. The LM3464A includes a fault handling mechanism which latches off output
channels upon open or short circuit of the LED strings, preventing substantial damages due to failures of the LEDs. The
number of output channel can be expanded by cascading
several LM3464A evaluation boards to achieve high luminous
output.
National Semiconductor
Application Note 2071
SH Wong
June 3, 2011
Standard Settings of the Evaluation Board
• Vin range 12V to 95V (LM3464A)
• 48V LED turn ON voltage
• 350mA LED current per channel
• 2kHz thermal foldback dimming frequency
Because the LM3464A evaluation board is designed to turn
on the LED strings at 48V rail voltage, applying excessive input voltage to this board will increase power dissipation on the
MOSFETs and could eventually damage the circuit. In order
to avoid permanent damages, it is not recommended not to
apply higher than 60V input voltage to this evaluation board.
This board is generally designed to drive 4 LED strings at
350mA which each sting contains 12 serial LEDs. For driving
LED strings of different configuration, the value of a few components should be adjusted following the descriptions in this
document.
Highlight Features
• Dynamic Headroom Control (DHC)
• Thermal foldback control
• High speed PWM dimming
• Minimum brightness limit for thermal foldback control
• Cascade operation for output channel expansion
• Vin Under-Voltage-Lockout
• Fault protection and indication
• Programmable startup voltage
• Thermal Shutdown
© 2011 National Semiconductor Corporation 301271 www.national.com
Evaluation Board Schematic
AN-2071
FIGURE 1. LM3464A Evaluation Board Schematic
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30127101
Bill of Materials
Designation Description Package Manufacturer Part # Vendor
U1 LED Driver IC, LM3464A eTSSOP-28 eTSSOP-28 LM3464AMH NSC
D1 Schottky Diode 40V 1.1A DO219AB DO219AB SL04-GS08 Vishay
Q1,Q2,Q3,Q4
CIN Cap MLCC 100V 2.2uF X7R 1210 1210 GRM32ER72A225KA35L Murata
CVCC Cap MLCC 10V 1uF X5R 0603 0603 GRM185R61A105KE36D Murata
CDHC Cap MLCC 50V 0.22uF X5R 0603 0603 GCM188R71H224KA64D Murata
CFLT Cap MLCC 50V 2.2nF X7R 0603 0603 GRM188R71H222KA01D Murata
CTHM Cap MLCC 50V 68nF X7R 0603 0603 GRM188R71H683KA01D Murata
R1 Chip Resistor 8.06Kohm 1% 0603 0603 CRCW06038K06FKEA Vishay
RTHM1 Chip Resistor 4.87Kohm 1% 0603 0603 CRCW06034K87FKEA Vishay
RTHM2 Chip Resistor 232ohm 1% 0603 0603 CRCW0603232RFKEA Vishay
RDMIN1 Chip Resistor 15.4Kohm 1% 0603 0603 CRCW060315K4FKEA Vishay
RDMIN2 Chip Resistor 1.05Kohm 1% 0603 0603 CRCW06031K05FKEA Vishay
RDHC Chip Resistor 2.67Kohm 1% 0603 0603 CRCW06032K67FKEA Vishay
RFB1 Chip Resistor 48.7Kohm 1% 0603 0603 CRCW060348K7FKEA Vishay
RFB2 Chip Resistor 2.67Kohm 1% 0603 0603 CRCW06032K67FKEA Vishay
RISNS1, RISNS2,
RISNS3, RISNS4
RIN, RD1, RD2, RD3,
RD4
VIN,PGND Banana Jack 5.3(mm) Dia 5.3 (mm) Dia. 575-8 Keystone
FAULTb,DIM, SYNC,
THM+, THM-,
AGND, VFB, VIN,
PGND, EN
LED1, LED2, LED3,
LED4
PCB LM3464EVAL PCB 82.5 X 60 (mm) 82.5 x 60 (mm) N/A NSC
RG1, R2, RG3, RG4 No Connection 0603
ZIN, Z1, Z2, Z3, Z4 No Connection SMA
MOSFET N-CH 150V 29A D-PAK D-PAK FDD2572 Fairchild
MOSFET N-CH 150V 50A TO252–3 TO252–3 IPD200N15N3 Infineon
Chip Resistor 1.13ohm 1% 0603 0603 CRCW06031R13FKEA Vishay
Chip Resistor 0ohm 1% 0603 0603 CRCW06030000Z0EA Vishay
Turret 2.35(mm) Dia 2.35 (mm) Dia. 1502-2 Keystone
Turret 2.35(mm) Dia 2.35 (mm) Dia. 1502-2 Keystone
Turret 2.35(mm) Dia 2.35 (mm) Dia. 1502-2 Keystone
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Connectors and Test Pins
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30127102
FIGURE 2. Typical Connection Diagram
Evaluation Board Quick Setup Procedures
Terminal Designation Description
VIN Power supply positive (+ve) connection
PGND Power supply negative (-ve) connection
AGND LM3464A analog signal ground
LED1 Output Channel 1 (Connect to cathode of LED string 1)
LED2 Output Channel 2 (Connect to cathode of LED string 2)
LED3 Output Channel 3 (Connect to cathode of LED string 3)
LED4 Output Channel 4 (Connect to cathode of LED string 4)
EN LM3464A enable pin (pull down to disable)
VFB Connect to voltage feedback node of primary power supply for DHC
FAULTb Acknowledgement signal for arising of ‘FAULT’
DIM PWM dimming signal input (TTL signal compatible)
SYNC Synchronization signal for cascade operation
THM+ Connect to NTC thermal sensor for thermal foldback control
THM- Connect to NTC thermal sensor for thermal foldback control
VLEDFB Connected to LM3464A VLedFB pin
OUTP Connected to LM3464A OutP pin
VCC LM3464A internal voltage regulator output
VDHC Connected to LM3464A VDHC pin
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AN-2071
Structure of the System
A LM3464A LED lighting system is basically consist of three
main parts, the LM3464A evaluation board, an AC/DC power
supply and an LED array containing four LED strings. In general, the LM3464A evaluation board can be regarded as four
independent current sources that the dropout voltages on the
current sources are being monitored by an internal circuit that
generates the DHC signal. The LM3464A evaluation board is
designed to drive 4 LED strings of 12 LEDs in series. With
350mA driving current for every LED string, the default total
output power of the LM3464A evaluation board is around
60W. In order to ensure proper operation, the AC/DC power
supply and LED array should be selected following the steps
presented in this document.
Selection of AC/DC Power Supply
The LM3464A evaluation board can be powered by an AC/
DC power supply through the banana-plug type connectors
on the board as shown in figure 2. Assuming the nominal forward voltage of one LED is 3.5V, the total forward voltage of
a LED string containing 12 LED is about 42V. In order to reserve extra voltage headroom to compensate the variations
of the LED forward voltages due to changes of operation temperature, the LED turn ON voltage of this evaluation board is
set to 48V. As this evaluation board is designed to deliver
350mA for each output channel, which is about 60W output
power at 48V rail voltage, the AC/DC power supply must be
able to supply no less than 60W continuous output power at
48V. Therefore, a 60W AC/DC power supply with 48V output
voltage is needed.
In order to facilitate Dynamic Headroom Control (DHC), the
output voltage of the AC/DC power supply is adjusted by the
LM3464A. The LM3464A adjusts the output voltage of the AC/
DC power supply by sinking current from the output voltage
feedback node of the AC/DC converter through a resistor
RDHC into the OutP pin according to the dropout voltage of
the linear current regulators. The OutP pin of the LM3464A is
a open drain pin that can only sink current from the voltage
feedback node of the AC/DC power supply, thus the
LM3464A evaluation board is only able to increase the output
voltage of the AC/DC power supply to acquire wider voltage
headroom.
Since the output voltage of the AC/DC converter will be increased by the LM3464A to allow dynamic head room control
(DHC), the nominal output voltage of the AC/DC power supply
must be reduced prior to connecting to the LM3464A evaluation board to reserve voltage headroom for DHC to take
place. This is achieved by modifying the resistance of the
output voltage sensing resistors of the AC/DC power supply.
To adapt the AC/DC power supply to the LM3464A evaluation
board, the nominal output voltage of the AC/DC power supply
is recommended to be reduced from 48V to 36V. Usually, the
nominal output voltage of the AC/DC power supply can be
reduced by changing the resistance of the resistor divider for
output voltage feedback. Figure 2 shows the voltage feedback circuit using LM431 which has been widely used in
typical AC/DC power supplies as an example.
To reduce the output voltage of the AC/DC power supply from
48V to 36V, the resistance of R2 is increased without changing
the value of R1. The output voltage and value of R2 are related
by the following equations:
(1)
For V
And V
REF(AC/DC)
RAIL(nom)
= 2.5V
= 36V:
(2)
In the above equations, V
of the AC/DC converter for output voltage feedback. V
is the objective rail voltage level being adjusted to. In this
(nom)
example, reducing of the rail voltage is achieved by increasing
REF(AC/DC)
is the reference voltage
RAIL
the value of R2. With the rail voltage is reduced to 36V, the
LED strings are unable to be driven at 350mA due to insufficient voltage headroom until the DHC loop functions. In order
to ensure the LED strings an regulated driving current at the
time that the LED stings being turned on, the LM3464A increases the output voltage of the AC/DC power supply
(V
) from 36V to 48V (V
RAIL
LED strings. The level of V
of the resistors, RFB1 and RFB2. Figure 3 shows the changes
of V
upon the AC/DC power supply is powered until the
RAIL
system enters steady state operation.
DHC_READY
DHC_READY
) prior to turning on the
is defined by the value
As the output voltage of the AC/DC power supply is depending on the current being sunk from the output voltage feedback node of the AC/DC power supply, the output voltage
could increase to exceed the rated output voltage of the AC/
DC power supply and damage the system if the resistance of
the RDHC is too low and the OutP pin of the LM3464A is accidentally shortened to GND (V
value of the RDHC must be selected appropriately following
the equations below. In the equations, V
imum voltage that V
to GND. R1 and R2 are the resistors of the output voltage
can reach if the OutP pin is shortened
RAIL
= 0V). To avoid this, the
OutP
RAIL(peak)
is the max-
feedback resistor divider of the AC/DC power supply. When
designing the values of the RDHC, it is essential to ensure
that the V
of the AC/DC power supply, otherwise the AC/DC power sup-
RAIL(peak)
does not exceed the rated output voltage
ply could be damaged.
(3)
where
(4)
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