LT3466EFE Linear Technology, LT3466EFE Datasheet - Page 9

• Manufacturer Part Number: LT3466EFE
• Description: IC,Laser Diode/LED Driver,TSSOP,16PIN,PLASTIC
• Manufacturer: Linear Technology

OPERATIO
However, the other converter will continue functioning
properly. The photo in Figure 4b shows circuit operation
with converter 1 output open-circuit and converter 2 driv-
ing eight LEDs at 20mA. Converter 1 starts switching at a
lower peak inductor current and begins skipping pulses,
thereby reducing its input current.
Figure 4b. Switching Waveforms with Output 1 Open-Circuit
200mA/DIV
100mA/DIV
50mA/DIV
Figure 4a. Transient Response of Switcher 1 with LED1
Disconnected from the Output
10V/DIV
50V/DIV
50V/DIV
V
V
V
OUT1
SW1
SW2
I
I
I
L1
L1
L2
V
CIRCUIT OF FIGURE 1
LED1 DISCONNECTED
V
CIRCUIT OF FIGURE 1
IN
IN
= 3.3V
= 3.3V
LED1 DISCONNECTED AT THIS INSTANT
U
200µs/DIV
1µs/DIV
3466 F04b
3466 F04a
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.
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 from
operating 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 = 15µH
C = 0.47µF
IN
= 3.6V
Figure 5. Start-Up Waveforms
100µs/DIV
3466 F05
LT3466
3466fa
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