(Notes 2 and 3) ...................................... –40°C to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range .................. –65°C to 125°C
Lead Temperature (Soldering, 10 sec)................... 300°C
38 37 36 35 34 33 32
VC1 1
LED1 2
CAP1 3
CAP2 4
LED2 5
RT 6
REF 7
LED3 8
CAP3 9
CAP4 10
LED4 11
VC4 12
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 2°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
orDer inForMAtion
LEAD FREE FINISH
LT3476EUHF#PBF
LT3476IUHF#PBF
LEAD BASED FINISH
LT3476EUHF
LT3476IUHF
TAPE AND REEL
LT3476EUHF#TRPBF
LT3476IUHF#TRPBF
TAPE AND REEL
LT3476EUHF#TR
LT3476IUHF#TR
PART MARKING*
3476
3476
PART MARKING*
3476
3476
PACKAGE DESCRIPTION
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
PACKAGE DESCRIPTION
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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
l
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
10µA ≥ I
REF
≥ –200µA
l
electricAl chArActeristics
CONDITIONS
Over CAP1-4/LED1-4 Operating Range
l
MIN
2.8
102
100
8
2.2
1.032
TYP
105
12
1.050
MAX
16
107
108
16
33.5
1.063
UNITS
V
mV
mV
mV
V
V
3476fb
V
ADJ1-4
= 100mV
2
LT3476
electricAl chArActeristics
PARAMETER
REF Line Regulation
Quiescent Current in Shutdown
Quiescent Current Idle
Quiescent Current Active (Not Switching)
Switching Frequency
The
l
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
2.8V ≤ V
IN
≤ 16V
SHDN
= 0V
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
0.003
0.1
5.5
22
2000
1000
200
1.26
84
–10
–20
76
90
98
20
0
210
3
Static Test
I
SW
= 1.3A to GND
SHDN
= 0V
33.5
PWM1-4 < 0.4V, CAP = LED = 5V
CAP = LED = 5V
l
l
MAX
10
30
2300
1150
240
UNITS
%/V
µA
mA
mA
kHz
kHz
kHz
V
%
%
%
Nominal RT Pin Voltage
Maximum Duty Cycle
V
ADJ1-4
Input Bias Current
VC1-4 Idle Input Bias Current
EAMP GM (∆I
VC
/∆V
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
100
20
nA
nA
µS
MΩ
1.5
2
350
0.1
35
2.5
5
100
A
mV
µA
V
nA
µA
V
V
µA
V
V
µA
70
0.4
1.5
16
l
l
30
0.4
1.5
50
100
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 junction temperature. Specifications over the –40°C to 85°C
operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3476I is guaranteed to meet performance specifications over the –40°C
to 125°C operating junction temperature range.
3476fb
3
LT3476
typicAl perForMAnce chArActeristics
150
T
A
= 25°C, unless otherwise noted.
Oscillator Frequency vs R
T
V(CAP-LED) Threshold vs V
ADJ
T
A
= 25°C
2.5
Current Limit vs Duty Cycle
10000
TYPICAL
V(CAP-LED) THRESHOLD (mV)
120
CURRENT LIMIT (A)
2
MINIMUM
F
OSC
(kHz)
90
1.5
1000
60
1
0.5
30
0
0
0.3
0.6
0.9
V
ADJ
(V)
1.2
1.5
3476 G01
0
0
20
60
40
DUTY CYCLE (%)
80
100
3476 G02
100
1
10
R
T
(k )
100
1000
3476 G03
V(CAP-LED) Threshold
vs Temperature, V
ADJ
= V
REF
108
107
CURRENT LIMIT (A)
106
105
104
103
102
–45
2.5
Switch Current Limit
vs Temperature
1150
OSCILLATOR FREQUENCY (kHz)
1100
1050
1000
950
900
Oscillator Frequency
vs Temperature
R
T
= 21k
V(CAP-LED) THRESHOLD (mV)
2
1.5
1
0.5
–20
55
30
80
5
TEMPERATURE (°C)
105
130
0
–45
–20
55
30
80
5
TEMPERATURE (°C)
105
130
850
–45
–20
55
30
80
5
TEMPERATURE (°C)
105
130
3476 G04
3476 G05
3476 G06
Reference Voltage
1.065
V(CAP-LED) THRESHOLD (mV)
108
107
106
105
104
103
102
V(CAP-LED) Threshold vs V(CAP)
V
ADJ
= 1.05V
25
20
INPUT CURRENT (mA)
Quiescent Current
PWM 1-4 = 3.6V
1.060
V
REF
(V)
1.055
15
10
V
C
= GND, NOT SWITCHING
T
A
= 25°C
1.050
PWM 1-4 = 0V
5
1.045
1.040
–45
–20
55
30
80
5
TEMPERATURE (°C)
105
130
0
5
10
20
15
V
CAP
(V)
25
30
35
0
0
4
8
V
IN
(V)
12
16
3476 G09
3476 G07
3476 G08
3476fb
4
LT3476
typicAl perForMAnce chArActeristics
SHDN
and PWM Pins Current vs
Voltage
120
100
80
60
40
20
0
SHDN
PWM 1-4
PIN THRESHOLD (V)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
–45
CAP1-4 OVERVOLTAGE THRESHOLD (V)
T
A
= 25°C, unless otherwise noted.
CAP Pins Overvoltage Threshold
vs Temperature
36.0
35.5
35.0
34.5
34.0
33.5
33.0
–45
SHDN
and PWM Pins Threshold
vs Temperature
CURRENT (µA)
0
4
8
PIN VOLTAGE (V)
12
16
3476 G10
–20
55
30
80
5
TEMPERATURE (°C)
105
130
–20
55
30
80
5
TEMPERATURE (°C)
105
130
3476 G11
3476 G12
pin Functions
VC1, VC4, VC3, VC2, (Pins 1, 12, 13, 38):
Error Ampli-
fier Compensation Pin. When PWM is low, VC 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.
RT (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 VC pin for the channel to become high impedance.
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