LM3553 Datasheet, PDF (12/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

LM3553
SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
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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 (I_LED < 1A) will help improve the LED efficiency of the LM3553.
M/F Pin Control Register
Multi-Function Pin Control/Options
MSB
Register Address: 0x20
LSB
1
1
1
OCL
OVP DATA MODE RESET
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
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.
RESET
0
1
1
Table 1. M/F Functionality Configuration Table
MODE
X
0
1
M/F Function
RESET
GPI
GPO
Current Step Time Register
Current Step Time
MSB
Register Address: 0x50
LSB
1
1
1
1
1
1
ST1
ST0
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
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:
T_{RAMPUP/RAMPDOWN} = (N_FLASH - N_START + 1) × t_STEP
where
• N is equal to the decimal value of the brightness level
• (0 ≤ N_FLASH ≤ 127 and 0 ≤ N_START ≤ 31)
N_START = N_TORCH if Torch is enabled before going into a flash. If going straight into a flash from an off-state,
N_START = 0.
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