Torch and

Charge (5.0V)

5.0V

3.0V

T2 bit

6HW WR µ0¶

Flash

200 mA

120 mA

60 mA

Time

Time

4.75V

LM3550

www.ti.com

SNVS569B – MAY 2009 – REVISED MAY 2013

NOTE

When the LM3550 is placed into Optimal Charge Mode, the flash LEDs will begin to glow

once the super-capacitor voltage exceeds 3.0V. The LEDs will continue to glow until the

part is placed into shutdown, into the flash state, or into one of the fixed voltage charge

modes.

TORCH AND CHARGE STATE

The Torch and Charge state provides the ability to utilize the torch functionality while charging to the selected

target voltage. The Torch and Charge state is entered by setting the Torch bit and Charge bit to a '1' and by

setting the Flash bit to a '0' in the General Purpose Register. Additionally, the CM1 and CM0 bits can be

configured to define the target charge voltage.

During the initial charging of the super-capacitor, the Torch functionality will not be enabled until the capacitor

voltage reaches 3.0V. Additionally, the Torch current is limited to 60 mA until the target voltage is reached. Once

the output reaches the target, the current level specified in the Current Control Register is allowed.

bit in the Current Control Register to a '0', decreasing the torch current.

Figure 47. Torch Current Diagram

FLASH STATE

When entered, the LM3550's Flash state delivers a high-current burst of current to the Flash LEDs. To enter the

Flash state, the Flash bit in the General Purpose Register must be set to a '1' or the STROBE pin must be pulled

F0 in Current Control and FD3-FD0 in Options).

By default, a flash will not occur if the super-capacitor is not fully charged (i.e., the end-of-charge flag (EOC pin)

automatically reset the Flash bit and the Torch bit to '0' upon completion of the flash. Additionally, after the flash

event has occurred, the LM3550 will return to the charge state/mode that was in operation before the flash event

with the exception of Optimal Charge Mode. (If Optimal Charge Mode was used before a flash, all charging is

halted after the flash.)

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