LM3553 Datasheet, PDF (13/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

LM3553
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Torch Current Control Register
MSB
TORCH Current Control
Register Address: 0xA0
SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
LSB
1
0
0
TC4
TC3
TC2
TC1
TC0
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
TC6-TC0: Sets Torch current level for D1 and D2. xxx1 1111 = Fullscale
Flash Current Control Register
FLASH Current Control
MSB
Register Address: 0xB0
LSB
1
FC6
FC5
FC4
FC3
FC2
FC1
FC0
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
FC6-FC0: Sets Flash current level for D1 and D2. x111 1111 = Fullscale
Current Level Equation
The Full-Scale Flash Current Level is set through the use of an external resistor (R_SET) connected to the I_SET pin.
The R_SET selection equation can be used to set the current through each of the two current sinks, D1 and D2.
R_SET = 6770 × 1.24V ÷ I_Dx
Table 2. R_SET Selection Table
I_Flash = ID1 + ID2
500mA
600mA
1A
1.2A
R_SET
33.6kΩ
28kΩ
16.8kΩ
14kΩ
The current through each current sink, D1 and D2, can be approximated by the following equation using the
values stored in either the Torch or Flash Current Control registers.
I_FLASH≊ (N + 1) × I_{LED_TOTAL} ÷ 128
where N is the decimal equivalent number (0 ≤ N ≤ 127 for Flash and 0 ≤ N ≤ 31 for Torch) stored in the Torch or
Flash Current control registers and I_{LED_TOTAL} = I_D1 + I_D2 @ Full-scale. Brightness codes 0 through 4 are repeated
and each sets the total LED current to approximately 40mA.
Flash Safety Timer Control Register
FLASH Duration Control
MSB
Register Address: 0xC0
LSB
1
1
1
1
FD3
FD2
FD1
FD0
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
FD3-FD0: Sets Flash Duration for D1 and D2. 1111 = Fullscale
Safety Timer Duration Code (Binary)
0000
0001
0010
0011
0100
0101
Typical Safety Timer Duration (milliseconds)
50
100
200
300
400
500
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