Copyright © 2016, Texas Instruments Incorporated

C1+

C1-

C2+

C2-

1.0-MHz

Switch

Frequency

VIN

GND

LM3550

2.7 V to 5.5 V

2X, 3/2X and 1X

Charge Pump

I

2C Interface

Block

General Purpose Register

Current Control Registers

Options Control Register

SDA

SCL

ALD/TEMP High

ALD/TEMP Low

Registers

Current

Limit

Controller

OVP

External

NFET

Controller

Active

Balance

Ambient

Light/

Temperature

Detection

EOC

STROBE

IND

VOUT

BAL

LED-

FB

FET_CON

ALD/TEMP

Output

Disconnect

Voltage

Mode FB

13

LM3550

www.ti.com

SNVS569C – MAY 2009 – REVISED OCTOBER 2016

Product Folder Links: LM3550

Submit Documentation Feedback

Copyright © 2009–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LM3550 is a super-capacitor charger and high-current-flash controller based upon a switched-capacitor

boost converter. On the charging end of the application, the LM3550 has a 534 mA (typical) input current limit

that prevents the part from drawing an excessive current when the super-capacitor voltage is below the target

charge voltage. During the charge phase the LM3550 runs in current limit and adaptively change gains (1×, 1.5×,

2×) until the super-capacitor reaches its target charge voltage. Integrated into the LM3550 is an external NFET

controller that allows the flash current drawn from the super-capacitor to remain regulated throughout the flash

cycle. Flash timing and current level can be changed through the I2C-compatible interface.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 STROBE Pin

The STROBE pin on the LM3550 provides an external method of flash triggering. This means a direct connection

between a controller or camera/imager and the LM3550 device can be made, avoiding any latency added due to

communication delays. The STROBE pin can be configured to be rising-edge sensitive (default) or level

sensitive. In the rising-edge sensitive mode, the flash duration is controlled internally and uses the value stored in

the FLASH duration bits (Options Control Register bits 3:0) to determine the pulse length. If level sensitive mode

is selected (Options Control Register bit 7 = 1), the flash-pulse duration can be controlled externally. In this

mode, when the STROBE pin is high, the flash remains on as long as the duration does not exceed the value

stored in the FLASH duration control bits. If the timing does exceed the internal flash-duration value, the LM3550

automatically disables the flash current.