LT3593 Просмотр технического описания (PDF) - Linear Technology

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LT3593

1MHz White LED Driver with Output Disconnect and One Pin Current Programming

Linear Technology 

LT3593

APPLICATIONS INFORMATION

Overvoltage Protection

The LT3593 has an internal open-circuit protection circuit.

In the case of an output open circuit, when the LEDs are

disconnected from the circuit or the LEDs fail open, VCAP

is clamped at 38V. The LT3593 will then switch at a very

low frequency to minimize input current. VCAP and input

current during output open circuit are shown in the Typical

Performance Characteristics. Figure 5 shows the transient

response when the LEDs are disconnected.

Low Input Voltage Applications

The LT3593 can be used in low input voltage applications.

The input supply voltage to the LT3593 must be 2.7V or

higher, but the inductor can be run off a lower battery

voltage. This technique allows the LEDs to be powered off

two alkaline cells. Most portable devices have a 3.3V logic

supply voltage which can be used to power the LT3593.

The LEDs can be driven straight from the battery, resulting

in higher efficiency.

Figure 6 shows three LEDs powered by two AA cells.

The battery is connected to the inductors and the chip is

powered off a 3.3V logic supply voltage.

IL

200mA/DIV

VCAP

20V/DIV

VSW

20V/DIV

VIN = 3.6V

400μs/DIV

3593 F05

FRONT PAGE

LEDs DISCONNECTED

APPLICATION CIRCUIT AT THIS INSTANT

Figure 5. Output Open-Circuit Waveform

L1

2 AA CELLS

10μH

D1

2V TO 3.2V

C1

C2

1μF

1μF

SW

3.3V

C3

VIN

CAP

1μF

LT3593

SHUTDOWN AND

CURRENT CONTROL

CTRL

LED

GND

3593 F06

C1: TAIYO YUDEN EMK107B5105MA

C2: MURATA GRM31MR71H105KA88

L1: MURATA LQH43CN100

D1: CENTRAL CMDSH05-4

Figure 6. Two AA Cells to Three White LEDs

3593f

9

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