1

bit7

1

bit6

1

bit5

1

bit4

FD3

bit3

FD2

bit2

FD1

bit1

FD0

bit0

MSB

LSB

FLASH Duration Control

Register Address: 0xC0

1

bit7

FC6

bit6

FC5

bit5

FC4

bit4

FC3

bit3

FC2

bit2

FC1

bit1

FC0

bit0

MSB

LSB

FLASH Current Control

Register Address: 0xB0

1

bit7

0

bit6

0

bit5

TC4

bit4

TC3

bit3

TC2

bit2

TC1

bit1

TC0

bit0

MSB

LSB

TORCH Current Control

Register Address: 0xA0

LM3553

www.ti.com

SNVS414B – FEBRUARY 2008 – REVISED MAY 2013

Torch Current Control Register

TC6-TC0: Sets Torch current level for D1 and D2. xxx1 1111 = Fullscale

Flash Current Control Register

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 (RSET) connected to the ISET pin.

The RSET selection equation can be used to set the current through each of the two current sinks, D1 and D2.

RSET = 6770 × 1.24V ÷ IDx

Table 2. RSET Selection Table

IFlash = ID1 + ID2

RSET

500mA

33.6k

Ω

600mA

28k

Ω

1A

16.8k

Ω

1.2A

14k

Ω

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.

IFLASH≊

≊ (N + 1) × ILED_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 ILED_TOTAL = ID1 + ID2 @ Full-scale. Brightness codes 0 through 4 are repeated

and each sets the total LED current to approximately 40mA.

Flash Safety Timer Control Register

FD3-FD0: Sets Flash Duration for D1 and D2. 1111 = Fullscale

Safety Timer Duration Code (Binary)

Typical Safety Timer Duration (milliseconds)

0000

50

0001

100

0010

200

0011

300

0100

400

0101

500

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