LM2755

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SNVS433D – OCTOBER 2007 – REVISED APRIL 2013

TIME STEP CONTROL

Bit 0 to Bit 2: The value of these 3 bits is equal to N, which is used in the timing control equations (0

≤ N ≤ 7).

The minimum internal time step (N=0) is 50µs. Setting the time-step to N=7 results in a maximum time step of

6.4msec.

tSTEP = 50µsec × 2

NSTEP if the internal clock is used.

(4)

tSTEP = 2

NSTEP × (32 ÷ f

SYNC ) if the external clock on the SYNC pin is used.

(5)

Bit 3 to Bit 7: Not used

DELAY CONTROL

The LM2755 allows the programmed current waveform on each diode pin to independently start with a delay

upon enabling the waveform dimming bits in the general purpose register. There are 256 delay levels available.

The delay time is set by the following equation:

For nSTEP= 0,

(6)

tdelayx = tSTEP × (ndelayx+ nrisex )

(7)

By default, ndelayx = 0 with a range of 0 ≤ ndelay ≤ 255.

(8)

For 1

≤ nSTEP ≤ 7, tdelayx = tSTEP × [(ndelayx-1) + (nrisex-1)]

where

•

1

≤ ndelay ≤ 255.

•

If ndelay = 0, tdelayx = 0s.

•

ndelayx is stored in the Dx Delay registers.

(9)

TIMING CONTROL

nrisex nfallx, nhighx, nlowx are numbers between 0 and 255, stored in the timing control registers. The durations of the

rise, high, fall and low times are given by:

For nSTEP= 0,

(10)

(11)

trise/fall = tSTEP x (nIDxH − nIDxL − 1 ) x nrisex/fallx

where

•

2

≤ nrisex/fallx ≤ 255

•

nrisex or nfallx = 0 or 1 are not valid and should not be used

(12)

For 1

≤ nSTEP ≤ 7,

(13)

trise/fall = tSTEP x (nIDxH− nIDxL − 1 ) x (nrisex/fallx − 1)

where

•

2

≤ nrisex/fallx ≤ 255

•

nrisex or nfallx = 0 or 1 are not valid and should not be used

(14)

For nSTEP= 0,

(15)

thighx = tSTEP × (nhighx + nfallx) tlowx = tSTEP × (nlowx + nrisex)

where

•

1

≤ nhighx/lowx ≤ 255

•

For nhighx/lowx=0, thigh or low = tSTEP

(16)

For 1

≤ nSTEP ≤ 7,

(17)

thighx = tSTEP × ((nhighx − 1) + (nfallx -1))

(18)

tlowx = tSTEP × ((nlowx − 1)+ (nrisex -1))

where

•

2

≤ nhighx/lowx ≤ 255

•

For nhighx/lowx= 0 or 1, thighx = tSTEP × (nfallx − 1)

•

tlowx = tSTEP × (nrisex − 1)

(19)

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