LT3466 Ver la hoja de datos (PDF) - Linear Technology
Número de pieza
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Fabricante
LT3466 Datasheet PDF : 20 Pages
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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.
VOUT1
10V/DIV
IL1
200mA/DIV
200µs/DIV
LED1 DISCONNECTED AT THIS INSTANT
VIN = 3.3V
CIRCUIT OF FIGURE 1
3466 F04a
Figure 4a. Transient Response of Switcher 1 with LED1
Disconnected from the Output
LT3466
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.
IL1
50mA/DIV
VSW1
50V/DIV
IL2
100mA/DIV
VSW2
50V/DIV
VIN = 3.3V
1µs/DIV
CIRCUIT OF FIGURE 1
LED1 DISCONNECTED
3466 F04b
Figure 4b. Switching Waveforms with Output 1 Open-Circuit
IIN
100mA/DIV
VOUT1
5V/DIV
VFB1
200mV/DIV
CRTL1
2V/DIV
VIN = 3.6V
4 LEDs, 20mA
L = 15µH
C = 0.47µF
100µs/DIV
3466 F05
Figure 5. Start-Up Waveforms
3466fa
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