LT3466 Linear Technology, LT3466 Datasheet - Page 9

• Manufacturer Part Number: LT3466
• Description: Dual Full Function White LED Step-Up Converter with Built-In Schottky Diodes
• Manufacturer: Linear Technology

OPERATIO
In the event one of the converters has an output open-
circuit, its output voltage will be clamped at 42V. However,
the other converter will continue functioning properly. The
photo in Figure 4 shows circuit operation with converter 1
output open-circuit and converter 2 driving eight LEDs at
20mA. Converter 1 switches at a lower frequency, reduc-
ing its input current.
Soft-Start
The LT3466 has a separate internal soft-start circuitry for
each converter. Soft-start helps to limit the inrush current
during start-up. Soft-start is achieved by clamping the
output of the error amplifier during the soft-start period.
This limits the peak inductor current and ramps up the
output voltage in a controlled manner.
500mA/DIV
200mA/DIV
50V/DIV
50V/DIV
V
V
SW1
SW2
I
I
L1
L2
Figure 4. Output 1 Open-Circuit Waveforms
V
CIRCUIT OF FIGURE 1
(8/8 LEDs)
IN
= 3.6V
U
1 s/DIV
3466 F04
The converter enters into soft-start mode whenever the
respective CTRL pin is pulled from low to high. Figure 5
shows the start-up waveforms with converter 1 driving
four LEDs at 20mA. The filtered input current, as shown in
Figure 5, is well controlled. The soft-start circuit is less
effective when driving a higher number of LEDs.
Undervoltage Lockout
The LT3466 has an undervoltage lockout circuit which
shuts down both the converters when the input voltage
drops below 2.1V (typ). This prevents the converter to
operate in an erratic mode when powered from low supply
voltages.
100mA/DIV
200mV/DIV
5V/DIV
2V/DIV
CRTL1
V
OUT1
V
FB1
I
IN
V
4 LEDs, 20mA
L = 15 H
C = 0.47 F
IN
= 3.6V
Figure 5. Start-Up Waveforms
100 s/DIV
3466 F05
LT3466
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