LT3474EFE#PBF Linear Technology, LT3474EFE#PBF Datasheet - Page 15

• Manufacturer Part Number: LT3474EFE#PBF
• Description: IC LED DRVR HP CONS CURR 16TSSOP
• Manufacturer: Linear Technology
• Type: High Power, Constant Currentr

Specifications of LT3474EFE#PBF

• Constant Current: Yes
• Topology: PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: Color, White LED
• Frequency: 200kHz ~ 2MHz
• Voltage - Supply: 3.5 V ~ 36 V
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 1A
• Internal Switch(s): Yes
• No. Of Outputs: 1
• Output Current: 1A
• Output Voltage: 15V
• Input Voltage: 4V To 36V
• Dimming Control Type: PWM
• Operating Temperature Range: -40°C To +85°C
• Driver Case Style: TSSOP
• Rohs Compliant: Yes
• Led Driver Application: Automotive, Avionic Lighting
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Efficiency: -

APPLICATIONS INFORMATION
BOOST and BIAS Pin Considerations
The capacitor and internal diode tied to the BOOST pin
generate a voltage that is higher than the input voltage.
In most cases, a 0.22μF capacitor will work well. Figure 4
shows three ways to arrange the boost circuit. The BOOST
pin must be more than 2.5V above the SW pin for full ef-
fi ciency. For outputs of 2.8V or higher, the standard circuit
(Figure 4a) is best. For lower output voltages, the BIAS pin
V
V
V
V
IN
IN2
IN
V
IN
IN
> 3V
Figure 4. Generating the Boost Voltage
V
MAX V
V
MAX V
MINIMUM VALUE FOR V
V
MAX V
BOOST
BOOST
V
MAX V
BOOST
BOOST
BOOST
BOOST
BIAS
V
BIAS
V
BIAS
V
BIAS
V
BOOST
– V
– V
BOOST
IN
IN
IN
IN
– V
– V
SW
SW
LT3474
LT3474
LT3474
LT3474
SW
SW
≈ V
≈ 2V
GND
GND
GND
GND
≈ V
≈ V
≈ V
≈ V
≈ V
≈ V
BOOST
IN2
BOOST
BOOST
BOOST
IN2
IN
IN
IN
IN
OUT
OUT
SW
+ V
SW
SW
+ V
(4c)
+ V
SW
(4b)
(4d)
(4a)
IN
– V
OUT
OUT
IN2
Z
= 3V
– V
Z
C3
C3
C3
C3
3474 F04c
3474 F04b
V
3474 F04d
OUT
3474 F04a
V
V
OUT
OUT
V
OUT
In order to have accurate LED current, precision resistors
are preferred (1% or better is recommended). Note that
the V
use the following formula to choose resistors:
can be tied to the input (Figure 4b). The circuit in Figure
4a is more effi cient because the BOOST pin current comes
from a lower voltage source. The BIAS pin can be tied to
another source that is at least 3V (Figure 4c). For example,
if a 3.3V source is on whenever the LED is on, the BIAS
pin can be connected to the 3.3V output. For LT3474-1
applications with higher output voltages, an additional
Zener diode may be necessary (Figure 4d) to maintain the
BOOST pin voltage below the absolute maximum. In any
case, be sure that the maximum voltage at the BOOST pin
is both less than 51V and the voltage difference between
the BOOST and SW pins is less than 25V.
Programming LED Current
The LED current can be set by adjusting the voltage on
the V
or to a 1.25V source. For lower output currents, program
the V
Voltages less than 1.25V can be generated with a voltage
divider from the REF pin, as shown in Figure 5.
R
I
LED
2
ADJ
ADJ
ADJ
=
=
Figure 5. Setting V
1 25
pin. For a 1A LED current, either tie V
using the following formula:
pin sources a small amount of bias current, so
1A • V
.
1.25V
V V
R
ADJ
–
1
V
R1
R2
ADJ
ADJ
REF
V
ADJ
+
LT3474/LT3474-1
ADJ
50
LT3474
GND
nA
with a Resistor Divider
3474 F04
ADJ
15
to REF
3474fd