FEATURES
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LT3476
High Current
Quad Output LED Driver
DESCRIPTIO
The LT
®
3476 is a quad output DC/DC converter designed
to operate as a constant-current source for driving high
current LEDs. A fixed frequency, current mode architecture
results in stable operation over a wide range of supply and
output voltages. A frequency adjust pin allows the user to
program switching frequency between 200kHz and 2MHz
to optimize efficiency and external component size.
The LT3476 senses output current at the high side of
the LED. High side current sensing is the most flexible
scheme for driving LEDs, allowing buck, boost or buck-
boost configurations. Each current monitor threshold is
trimmed to within 2.5% at the full scale of 105mV. With
an external sense resistor, the user programs the output
current range of each channel. Each of the four regulators
is independently operated by that channel’s PWM signal.
This PWM feature allows precise adjustment of the color
mixing or dimming ratio of the LED source. Dimming
ratios up to 1000:1 can be achieved.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
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True Color PWM
TM
Dimming Delivers Up to 5000:1
Dimming Ratio (In Boost Configuration)
LED Current Regulation with High-Side Sense
VADJ Pin Accurately Sets LED Current Sense
Threshold Over Range 10mV to 120mV
Four Independent Driver Channels with 1.5A, 36V
Internal NPN Switches
Frequency Adjust Pin: 200kHz to 2MHz
High Efficiency Conversion = Up to 96%
Open LED Protection
Low Quiescent Current
22mA in Active Mode
<10μA in Shutdown Mode
Wide V
IN
Range: 2.8V to 16V
Thermally Enhanced, 38-Lead, 5mm × 7mm
QFN Package
APPLICATIO S
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RGGB Lighting
Automotive and Avionic Lighting
TFT LCD Backlighting
Constant-Current Sources
TYPICAL APPLICATIO
PV
IN
33V
CAP1
100mΩ
LED1
100W Quad 1A
×
8 LED Driver
CAP2
100mΩ
LED2
CAP3
100mΩ
LED3
CAP4
100mΩ
LED4
2.2μF
×
4
UP TO
8 LEDS
1A
0.22μF
0.22μF
1A
1A
0.22μF
0.22μF
1A
I
LED
500mA/DIV
10μH
10μH
10μH
10μH
1.05V
V
IN
2.8V TO 16V
PWM1-4
SHDN
2.2μF
SW1
CAP1-4
LED1-4
V
IN
PWM1-4
SHDN
SW2
LT3476
SW3
SW4
REF
VADJ1-4
VC1-4
R
T
3476 TA01
4.99k
100k
21k
GND
1nF
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1000:1 PWM Dimming at 100Hz
PWM
5V/DIV
5μs/DIV
3476 TA02
1
LT3476
ABSOLUTE
(Note 1)
AXI U RATI GS
PI CO FIGURATIO
TOP VIEW
PWM1
PWM2
V
ADJ1
V
ADJ2
VC2
V
IN
............................................................................16V
PWM1-4,
SHDN
........................................................16V
SW1-4, LED1-4, CAP1-4 ...........................................36V
REF R
T
, V
ADJ1-4
, V
C
1-4 ................................................2V
,
Operating Temperature Range (Note 2).... –40°C to 85°C
Maximum Junction Temperature........................... 125°C
Storage Temperature Range................... –65°C to 125°C
Lead Temperature ................................................. 300°C
V
IN
38 37 36 35 34 33 32
VC1 1
LED1 2
CAP1 3
CAP2 4
LED2 5
R
T
6
REF 7
LED3 8
CAP3 9
CAP4 10
LED4 11
VC4 12
13 14 15 16 17 18 19
V
ADJ4
V
ADJ3
PWM4
PWM3
SHDN
VC3
NC
39
GND
31 NC
30 NC
29 SW1
28 SW1
27 SW2
26 SW2
25 SW3
24 SW3
23 SW4
22 SW4
21 NC
20 NC
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS GND
(MUST BE SOLDERED TO PCB)
ORDER I FOR ATIO
LEAD FREE FINISH
LT3476EUHF#PBF
LEAD BASED FINISH
LT3476EUHF
TAPE AND REEL
TAPE AND REEL
LT3476EUHF#TR
PART MARKING
3476
PART MARKING
3476
PACKAGE DESCRIPTION
38-Lead (5mm × 7mm) Plastic QFN
PACKAGE DESCRIPTION
38-Lead (5mm × 7mm) Plastic QFN
LT3476EUHF#TRPBF
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
●
denotes the specifications which apply over the full operating
temperature range, (Note 3) otherwise specifications are at T
A
= 25°C. SW1-4 = 5V, V
IN
= 3.3V,
SHDN
= 3.3V, R
T
= 21k to GND,
PWM1-4 = 3.3V, V
ADJ1-4
= REF CAP1-4 = 5V, unless otherwise noted.
,
PARAMETER
V
IN
Operating Range
Full-Scale LED Current Monitor Threshold
One-Tenth Scale LED Current Monitor Threshold
CAP1-4/LED1-4 Operating Range
REF Output Voltage
REF Line Regulation
Quiescent Current in Shutdown
10μA ≥ I
REF
≥ –200μA
2.8V ≤ V
IN
≤ 16V
SHDN
= 0V
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
Over CAP1-4/LED1-4 Operating Range
●
MIN
2.8
102
100
8
2.2
1.032
TYP
105
12
1.050
0.003
0.1
NC
V
ADJ1-4
= 100mV
2
U
TEMPERATURE RANGE
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
MAX
16
107
108
16
36
1.063
10
UNITS
V
mV
mV
mV
V
V
%/V
μA
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W W
W
W
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LT3476
ELECTRICAL CHARACTERISTICS
PARAMETER
Quiescent Current Idle
Quiescent Current Active (Not Switching)
Switching Frequency
The
●
denotes the specifications which apply over the full operating
temperature range, (Note 3) otherwise specifications are at T
A
= 25°C. SW1-4 = 5V, V
IN
= 3.3V,
SHDN
= 3.3V, R
T
= 21k to GND,
PWM1-4 = 3.3V, V
ADJ1-4
= REF CAP1-4 = 5V, unless otherwise noted.
,
CONDITIONS
PWM1-4 = 0V
VC1-4 = 0V
R
T
= 8.25k
R
T
= 21k
R
T
= 140k
R
T
= 8.25k (2MHz)
R
T
= 21k (1MHz)
R
T
= 140k (200kHz)
Current Out of Pin
PWM1-4 = 0V
1700
850
160
MIN
TYP
5.5
22
2000
1000
200
1.26
84
–10
–20
76
90
98
20
0
200
3
Static Test
I
SW
= 1.3A to GND
SHDN
= 0V
33.5
PWM1-4 < 0.4V, CAP = LED = 5V
CAP = LED = 5V
1.5
16
1.5
50
100
30
0.4
70
0.4
1.5
2
350
0.1
35
100
5
2.5
100
20
30
2300
1150
240
MAX
UNITS
mA
mA
kHz
kHz
kHz
V
%
%
%
nA
nA
μS
MΩ
A
mV
μA
V
nA
μA
V
V
μA
V
V
μA
Nominal R
T
Pin Voltage
Maximum Duty Cycle
V
ADJ1-4
Input Bias Current
VC1-4 Idle Input Bias Current
EAMP GM (ΔI
VC
/ΔV
CAP-LED
)
VC Output Impedance
SW1-4 Current Limit
SW1-4 V
CESAT
SW1-4 Leakage Current
CAP1-4 Overvoltage Protect Threshold
CAP1-4/LED1-4 Idle Input Bias Current
CAP1-4/LED1-4 Input Bias Current
SHDN
Input Low Voltage
SHDN
Input High Voltage
SHDN
Pin Current
PWM1-4 Input Low Voltage
PWM1-4 Input High Voltage
PWM1-4 Pin Current
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 3:
The LT3476E is guaranteed to meet specifications from 0°C to
85°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
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LT3476
TYPICAL PERFOR A CE CHARACTERISTICS
V(CAP-LED) Threshold vs V
ADJ
150
T
A
= 25°C
2.5
TYPICAL
V(CAP-LED) THRESHOLD (mV)
120
CURRENT LIMIT (A)
2
MINIMUM
F
OSC
(kHz)
90
60
30
0
0
0.3
0.6
0.9
V
ADJ
(V)
1.2
V(CAP-LED) Threshold
vs Temperature, V
ADJ
= V
REF
108
107
CURRENT LIMIT (A)
106
105
104
103
102
–45
2.5
2
OSCILLATOR FREQUENCY (kHz)
V(CAP-LED) THRESHOLD (mV)
–20
55
30
5
TEMPERATURE (°C)
Reference Voltage
1.065
108
107
106
105
104
103
102
V(CAP-LED) THRESHOLD (mV)
1.060
INPUT CURRENT (mA)
V
REF
(V)
1.055
1.050
1.045
1.040
–45
–20
55
30
5
TEMPERATURE (°C)
4
U W
3476 G01
T
A
= 25°C, unless otherwise noted.
Current Limit vs Duty Cycle
10000
Oscillator Frequency vs R
T
1.5
1000
1
0.5
1.5
0
100
0
20
60
40
DUTY CYCLE (%)
80
100
3476 G02
1
10
R
T
(kΩ)
100
1000
3476 G03
Switch Current Limit
vs Temperature
1150
1100
1050
1000
950
900
Oscillator Frequency
vs Temperature
R
T
= 21k
1.5
1
0.5
80
105
0
–45
–20
55
30
5
TEMPERATURE (°C)
80
105
3476 G05
850
–45
–20
55
30
5
TEMPERATURE (°C)
80
105
3476 G06
3476 G04
V(CAP-LED) Threshold vs V(CAP)
V
ADJ
= 1.05V
25
Quiescent Current
PWM 1-4 = 3.6V
20
V
C
= GND, NOT SWITCHING
T
A
= 25°C
15
10
PWM 1-4 = 0V
5
0
0
5
10
20
15
V
CAP
(V)
25
30
35
80
105
3476 G07
0
4
8
V
IN
(V)
12
16
3476 G09
3476 G08
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LT3476
PI FU CTIO S
VC1, VC4, VC3, VC2, (Pins 1, 12, 13, 38):
Error Amplifier
Compensation Pin. When PWM is low, V
C
pin floats external
compensation capacitor to save state for next cycle.
LED1, LED2, LED3, LED4, (Pins 2, 5, 8, 11):
Non-
Inverting Input of Current Sense Error Amplifier. Connect
directly to LED current sense resistor terminal. Switcher
will regulate this node to a voltage of 0.1 • V
ADJ
below the
CAP node. Also connected to CAP node through external
sense resistor and to anode of LED string. Do not allow
this pin to float independently of corresponding CAP input
pin. In applications where the LED current is low and the
PV
IN
changes widely, connect the output filter capacitor
to LEDn.
CAP1, CAP2, CAP3, CAP4, (Pins 3, 4, 9, 10):
Inverting
input of current sense error amplifier. Connect directly to
other terminal of LED current sense resistor. Also con-
nected to output filter capacitor and cathode of external
Schottky rectifier. CAP greater than the overvoltage protect
threshold will inhibit switching.
R
T
(Pin 6):
Oscillator Programming Pin. Place resistor
connected to GND to program oscillator frequency.
REF: (Pin 7):
Reference Output Pin. Connect to V
ADJ
pin
to get full-scale LED current. Connect to resistor dividers
to program V
ADJ
pins to values lower than 1.05V. Bypass
to local GND with 0.1μF capacitor.
V
ADJ4
,
V
ADJ3
,
V
ADJ2
,
V
ADJ1
,
(Pins 14, 15, 36, 37):
LED
Current Adjustment Pin. Sets voltage across external sense
resistor between CAPn and LEDn. Connect directly to
REF for full-scale threshold of 105mV, or use signal vales
between GND and REF to modulate LED current. V
ADJ
pin
input range is 1.25V maximum.
PWM4, PWM3, PWM2, PWM1, (Pins 16, 17, 34, 35):
Signal low turns off the channel—disables the main
switch, reduces quiescent supply current to the channel,
and causes the V
C
pin for the channel to become high
impedance.
SHDN
(Pin 18):
Shutdown Pin. Higher than 1.5V turns
the device on.
NC (Pins 19, 20, 21, 30, 31, 32):
Not Used. Connect to
GND (Pin 39) for better heat dissipation.
SW4, SW3, SW2, SW1, (Pins 22, 23, 24, 25, 26, 27, 28, 29):
Switch Pin. Connect to external inductor and anode of external
Schottky rectifier. Minimize area of SW trace and use a
GND plane to reduce EMI. Adjacent pins of same name
are internally connected.
V
IN
(Pin 33):
Input Supply Pin. Must be locally by-
passed.
GND (Pin 39):
Signal and Power GND. Solder Exposed
Pad directly to ground plane. The Exposed Pad metal of
the package provides both electrical contract to ground
and good thermal contact to the printed circuit board.
It must be soldered to the circuit board for proper
operation.
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