LM3550SPXSLASHNOPB datasheet(16/43 Pages) TI2

16 / 43 page

Shutdown

Charge

Flash

Charge and

Torch

Optimal

Charge

Mode

Voltage

Mode

Charge

VBAT

ESR

CSC

Charger

VLED

VFB

IFLASH

VSC

100 mV

VRDSON

VHR

VCAP

LM3550

SNVS569C – MAY 2009 – REVISED OCTOBER 2016

www.ti.com

Product Folder Links: LM3550

Submit Documentation Feedback

7.3.9 Maximum Flash Duration

Several factors determine the maximum achievable flash pulse duration. The flash current magnitude, feedback

voltage, RDSON of the current source FET, super-capacitor capacitance (CSC), super-capacitor ESR (RESR) and

super-capacitor charge voltage (VCAP) determine the ability of the device to regulate the flash current for a given

amount of time.

tFLASH (maximum) = (CSC × VDROOP) / IFLASH

where

•

VDROOP = VCAP − VLED − [IFLASH × (RESR + RDSON + {RBAL/N)}] − VFB

•

N = number of flash LEDs

(5)

Example:

If VCAP = 5.3 V, VLED = 4 V (at 1.5 A), IFLASH (total) = 3 A, CSC = 0.5 F, RESR = 50 mΩ, RDSON = 40 mΩ,

VFB = 100 mV, and RBAL = 75 mΩ, then VDROOP = 0.82 V and tFLASH (maximum) = 136 ms.

Figure 37. Power Loss Model

7.4 Device Functional Modes

7.4.1 State Machine Description

Figure 38. Default State Diagram

LM3550SPX/NOPB Datasheet(PDF) 16 Page - Texas Instruments

LM3550SPX/NOPB Datasheet(HTML) 16 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Datasheet Download

Link URL