LM3565

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SNVS957 – JANUARY 2013

FUNCTIONAL DESCRIPTION

Circuit Description

Overview

The LM3565 is a high-power white LED flash driver capable of delivering up to 930 mA of LED current into two

series LEDs. 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.

Circuit Components

Synchronous Boost Converter

The LM3565 operates in boost mode in LED Flash or Assist operation. In LED boost mode, the PWM converter

switches and maintains at least 300 mV across the current source. This minimum headroom voltage ensures that

the current sink remains in regulation.

High-Side Current Source

The High-Side current source of the LM3565 is capable of driving two LEDs in series. The flash current range is

480 mA to 930 mA in 30 mA steps with a default current equal to 750 mA.

Additionally, the high-side current source is capable of supporting two Assist/Torch current levels (continuous

current) equal to 60 mA (default) or 90 mA.

A/D Converter

An internal 8-bit ADC can be utilized to measure the input voltage and the LED voltage during a flash or assist

event. If the ADC input voltage measurement bit is set to a '1' (IV bit in register 0x09), the digitized value of the

LM3565's input voltage can be read back from the Input Voltage ADC Register (0x0A). The input voltage is

sampled before the start of the flash or assist event if the FON bit in register 0x09 is set to a '0' and 2ms after the

LED current ramp up is completed if it is set to a '1'. The LED voltage can be read back from the LED Voltage

ADC Register (0x0B) if the ADC LED voltage measurement bit is set to a '1' (LV bit in register 0x09). The LED

voltage is sampled 2ms after the LED current is ramped up.

ENABLE Pin

The ENABLE pin on the LM3565 places the part into Shutdown Mode (low) or Standby Mode (high). In

Shutdown Mode, most of the control functionality is disabled. In shutdown, it is possible to enable the part

the Torch and Strobe pins if the part has been configured to do so. The ENABLE pin must be held low before

power is applied to the LM3565.

SDA and SCL Pins

input and SCL is the interface clock input.

STROBE Pin

The Strobe pin of the LM3565 provides an external method for initiating a flash or assist event. In most cases,

the Strobe pin is connected to an imaging module so that the image capture and flash event are synchronized.

The Strobe pin is only functional when the LM3565's Output Enable (OEN in 0x07) and Strobe Signal Mode

(SEN in 0x06) bits are set ('1'). The Strobe pin can be configured to be an edge-sensitive or level-sensitive input

by setting the Strobe Signal Usage bit (SSU in 0x06. '1' = Level, '0' = Edge). In edge-sensitive mode, a rising

edge transition ('0' to '1') will start the flash event and the internal flash timer will terminate the event. In level-

sensitive mode, a rising edge transition ('0' to '1') will start the flash event and a falling edge transition ('1' to '0')

or the internal flash timer, which ever occurs first, will terminate the event.

Additionally, the Strobe pin can be used to pulse-width modulate (PWM) the diode current during a flash or assist

event. In flash mode, by setting the PWM bit in the Strobe signaling register (PWM in register 0x06) to a '1', and

toggling the Strobe pin high and low, the diode current will transition between the target flash current and a

reduced current value selected in register 0x06 (SPL3-SPL0). When the Strobe pin is high ('1'), the flash current

is equal to the target LED current. When the Strobe pin is low ('0'), the flash current is equal to the target LED

current minus the reduction current value, or 60 mA, whichever is higher. The diode current is ramped up and

down during the transitions between the full current state and the reduced current state.

Copyright © 2013, Texas Instruments Incorporated

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Product Folder Links: LM3565