1

bit7

1

bit6

1

bit5

1

bit4

1

bit3

1

bit2

ST1

bit1

ST0

bit0

MSB

LSB

Current Step Time

Register Address: 0x50

1

bit7

1

bit6

1

bit5

OCL

bit4

OVP

bit3

DATA

bit2

MODE

bit1

RESET

bit0

MSB

LSB

Multi-Function Pin Control/Options

Register Address: 0x20

LM3553

SNVS414B – FEBRUARY 2008 – REVISED MAY 2013

www.ti.com

VFB: Selects the regulation voltage for the LM3553. Setting this VFB bit to a '0' sets the regulation voltage to

450mV while setting the VFB bit to a '1' sets the regulation voltage to 350mV. Setting the VFB bit to a '1' during

torch mode and/or lower current flash modes (ILED < 1A) will help improve the LED efficiency of the LM3553.

M/F Pin Control Register

RESET: Enables M/F as hardware RESET. '0' = Hardware RESET, .'1' = GPIO or current sink depending on the

MODE bit. Default = '0'

MODE: Sets M/F mode. Default for M0DE = '0'. '0' = GPI, and'1' = GPO

NOTE

When M/F is configured as an input, data is transfered from GPI to DATA whenever an

I2C write command is issued to the LM3553. When configuring M/F as a GPO, the first

write needs to take the LM3553 out of RESET mode and a second write can then set the

pin to the GPO.

DATA: GPIO Data. When the M/F is configured as an output (GPO), DATA sets the GPO level. Example: DATA

= '1', M/F is set high or logic '1'. When the M/F pin is configured as an input (GPI), DATA stores the GPI level.

Example: M/F = '1', DATA will be set to a '1'. Default for DATA = '0'.

OVP: Enables high-voltage OVP (OVP Bit ='1') or low-voltage OVP (OVP Bit ='0'). Default = low-voltage mode '0'

OCL: SW Pin Current Limit Selector Bit: If OCL = '0', the inductor current limit is 2.5A typ. If OCL = '1', the

inductor current limit is 1.7A typ.

Table 1. M/F Functionality Configuration Table

RESET

MODE

M/F Function

0

X

RESET

1

0

GPI

1

1

GPO

Current Step Time Register

ST1-ST0: Sets current level stepping time for D1 and D2 during the beginning and end of the flash or torch

current waveform. '00' = 25µs, '01' = 50µs, '10' = 100µs, '11' = 200µs.

The current ramp-up/ramp-down times can be approximated by the following equation:

TRAMPUP/RAMPDOWN = (NFLASH - NSTART + 1) × tSTEP

where

•

N is equal to the decimal value of the brightness level

•

(0

≤ NFLASH ≤ 127 and 0 ≤ NSTART ≤ 31)

NSTART = NTORCH if Torch is enabled before going into a flash. If going straight into a flash from an off-state,

NSTART = 0.

12

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