LT3466EDD-1 Ver la hoja de datos (PDF) - Linear Technology

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LT3466EDD-1

White LED Driver and Boost Converter in 3mm × 3mm DFN Package

Linear Technology 

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OPERATIO

In the event one of the converters has an output open-circuit,

its output voltage will be clamped at 39.5V. 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 driving the OLED display. Con-

verter 1 starts switching at a lower inductor current and

begins skipping pulses, thereby reducing its input current.

Converter 2 continues functioning properly.

VOUT1

10V/DIV

IL1

200mA/DIV

200µs/DIV

LED1 DISCONNECTED AT THIS POINT

VIN = 3.3V

CIRCUIT OF FIGURE 1

34661 F04a

Figure 4a. Transient Response of Switcher 1 with LED1

Disconnected from the Output

LT3466-1

Soft-Start

The LT3466-1 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 six

LEDs at 20mA. The filtered input current, as shown in

Figure 5, is well controlled. The soft-start circuitry is less

effective when driving a higher number of LEDs.

Undervoltage Lockout

The LT3466-1 has an undervoltage lockout circuit which

shuts down both converters when the input voltage drops

below 2.1V (typ). This prevents the converter from switch-

ing in an erratic mode when powered from low supply

voltages.

VSW1

50V/DIV

IL1

100mA/DIV

VSW2

50V/DIV

IL2

100mA/DIV

VIN = 3.6V

1µs/DIV

CIRCUIT OF FIGURE 1

34661 F04b

Figure 4b. Output 1 Open-Circuit Waveforms

IIN

200mA/DIV

VOUT1

20V/DIV

VFB1

200mV/DIV

CTRL1

5V/DIV

VIN = 3.6V

6 LEDs, 20mA

200µs/DIV

CIRCUIT OF FIGURE 1

34661 F05

Figure 5. Start-Up Waveforms

34661f

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