AS1130-BSST datasheet(55/67 Pages) AMSOSRAM

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[v2-01] 2016-Oct-12

AS1130 − Typical Application

LED Current Calculation

The current through a LED in the matrix is set via three registers

(Current Source Register, Dot Correction and PWM). The

resulting current through the single LED can be calculated as

shown in the following.

First it is necessary to calculate the time how long one LED will

be ON.

Where:

tLEDon: Time where the LED is ON

PWM:. Value set in the register (0 - 256), see Figure 36

fOSC: Frequency set in the CLK Synchronization Register, see

Figure 50.

The refresh rate is defined by the scan-limit and fOSC.

Where:

tREFRESH: Time needed to refresh the matrix scan-limit. is set via

the Display Option Register (0 - 11), see Figure 43

fOSC: frequency set in the CLK Synchronization Register, see

Figure 50

With the LED on-time and the refresh rate an average LED ON

factor can be calculated.

The resulting current is then the Segment Current (set in the

Current Source Register) times the average LED ON factor.

Where:

ISEG: Segment Current set via register Figure 44

Example:

Assume that following conditions are set in the registers:

PWM = 256, scan-limit = 5 (half filled matrix, 66 LEDs),

ISEG = 30mA

(EQ1)

tLEDon

PWM

fOSC

---------------

(EQ2)

tREFRESH

scanlimit 1

() 256

fOSC

------------------------------------------------------

(EQ3)

LEDonavg

tLEDon

tREFRESH

------------------------

PWM

scanlimit 1

() 256

------------------------------------------------------

(EQ4)

ILEDavg

ISEG LEDonavg

ISEG

PWM

scanlimit 1

() 256

------------------------------------------------------

(EQ5)

ILEDavg

30mA

256

() 256

--------------------------------

5mA

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