LT3476EUHF#PBF Linear Technology, LT3476EUHF#PBF Datasheet - Page 6

• Manufacturer Part Number: LT3476EUHF#PBF
• Description: IC LED DRVR HP CONST CURR 38-QFN
• Manufacturer: Linear Technology
• Type: High Power, Constant Currentr

Specifications of LT3476EUHF#PBF

• Constant Current: Yes
• Topology: PWM, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 4
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: Color, RGB
• Frequency: 200kHz ~ 2MHz
• Voltage - Supply: 2.8 V ~ 16 V
• Voltage - Output: 2.2 V ~ 36 V
• Mounting Type: Surface Mount
• Package / Case: 38-QFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 1.5A
• Internal Switch(s): Yes
• Efficiency: 96%
• Led Driver Application: Automotive, Avionic Lighting
• No. Of Outputs: 4
• Output Current: 1.5A
• Output Voltage: 36V
• Dimming Control Type: PWM
• Rohs Compliant: Yes
• Input Voltage: 2.8V To 16V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

BLOCK DIAGRA
OPERATIO
LT3476
The LT3476 is a constant-frequency, current mode regula-
tor with an internal power switch. Operation can be best
understood by referring to the Block Diagram. At the
start of each oscillator cycle, the SR latch is set, which
turns on the Q1 power switch. A voltage proportional to
the switch current is added to a stabilizing ramp and the
resulting sum is fed into the positive terminal of the PWM
comparator, A2. When this voltage exceeds the level at
the negative input of A2, the SR latch is reset, turning off
the power switch. The level at the negative input of A2 is
set by the error amplifi er A1, and is simply an amplifi ed
version of the difference between the voltage across the
internal resistor R
current sense resistor R
amplifi er sets the correct peak switch current level to
regulate the current through R
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
6
PV
33V
V
3V
IN
IN
33
7
REF
V
14, 15,
36, 37
PWM
16, 17,
34, 35
V
1, 12, 13, 38
V
U
SET
ADJ
C
IN
1.05V
and the voltage across the external
IDLE MODE
1.25V
–
+
SNS
W
CAP
3, 4, 9, 10
+
+
–
R
SNS
. In this manner, the error
R
2kΩ
A4
0.1Ω
SET
SNS
(EXT)
. If the error amplifi er’s
V1
LED
2, 5, 8, 11
Q3
EXTERNAL COMPONENTS
Q4
R
20kΩ
THERMAL
SET1
+
–
ISRC
300μA
BUCK MODE
145°C
LIMIT
AMPLIFIER
A1
ERROR
Q2
OSCILLATOR
GENERATOR
to 2MHz
200kHz
RAMP
∑
6
R
T
–
+
25k
35V
OVERVOLTAGE
A2
COMPARATOR
The current regulated in R
ing the voltage across R
amplifi er A4 regulates current in Q3 to produce a voltage
across R
transistor Q3 also produces a voltage across R
tenth the magnitude of the V
to the CAP input. The voltage across R
125mV (typ) by the separate 1.25V input on A4.
The average current regulated in R
for dimming using the PWM pin. When the PWM pin is
low, switching is disabled and the error amplifi er is turned
off so that it does not drive the V
loads on the V
of the V
capacitor. This feature reduces transient recovery time
because when the PWM input again transitions high, the
demand current for the switch returns to the value just
before PWM last transitioned low.
DETECT
PWM
C
2.2μF
NC
19, 20, 21
30, 31, 32
BYP
PWM
C
LED ARRAY
SET
pin will be saved on the external compensation
equal to V
C
pin are disabled so that the charge state
R
S
SHUTDOWN
Q
C
0.1μF
DRIVER
CURRENT SENSE
FILT
ADJ
SET
AMPLIFIER
LT3476 CHANNEL
SNS
. This current fl owing through
A3
using the V
10μH
+
–
ADJ
18
can be adjusted by chang-
SHDN
SNS
input and level shifted
C
Q1 MAIN
SW
22-29
0.02Ω
pin. Also, all internal
R
SWITCH
SW
can also be adjusted
ADJ
3476 BD
SET
input pin. The
is limited to
SET
one-
3476fa