40 s/DIV

VIN

200 mV/

DIV

ILED

200 mA/

DIV

400 s/DIV

500 mA/

DIV

VOUT

2V/DIV

TX

ILED

2V/DIV

1 s/DIV

500 mA/

DIV

VOUT

2V/DIV

TX

ILED

2V/DIV

400 s/DIV

1A/DIV

VIN

200 mV/

DIV

ILED

IIN

1A/DIV

400 s/DIV

1A/DIV

VIN

200 mV/

DIV

ILED

IIN

1A/DIV

LM3556

www.ti.com

SNVS796C – AUGUST 2011 – REVISED APRIL 2013

TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Input Voltage Flash Monitor, Up and Down Mode

Input Voltage Flash Monitor, Up and Down Mode

(0mv Hysteresis, 512 µs Filter Time)

(256µs Flash Ramp, 1/2 Step Filter Time)

Figure 26.

Figure 27.

Time Taken for LM3556 to Ramp

Impact on LED Current with a TX Event

from Torch to Flash after TX Event

Figure 28.

Figure 29.

from 3

→ 2.9V

Figure 30.

LM3556 GENERAL INFORMATION

The LM3556 is a high-power white LED flash driver capable of delivering up to 1.5A into a single high-powered

LED. The device incorporates a 4 MHz constant frequency-synchronous current-mode PWM boost converter,

and a single high-side current source to regulate the LED current over the 2.5V to 5.5V input voltage range.

minimum headroom voltage ensures that the current source remains in regulation. If the input voltage is above

the LED voltage + current source headroom voltage the device does not switch and turns the PFET on

LED is dropped across the current source.

Copyright © 2011–2013, Texas Instruments Incorporated

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