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AS1130

Datasheet - Ty p i c a l A p p l i c a t i o n

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’s necessary to calculate the time how long one LED will be ON.

Where:

PWM . . . value set in the register (0 - 256), (see Table 11 on page 18)

Where:

scan-limit . . . is set via the Display Option Register (0 - 11), (see Table 18 on page 24)

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:

Example:

(EQ 1)

t

LEDon

PWM

f

OSC

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

=

(EQ 2)

t

REFRESH

scanlimit

1

+

(

) 256

×

f

OSC

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

=

(EQ 3)

LEDon

av g

t

LEDon

t

REFRE SH

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

PWM

scanlimit

1

+

(

) 256

×

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

=

=

(EQ 4)

I

LEDavg

I

SEG

LEDon

avg

×

I

SEG

PWM

scanlimit

1

+

(

) 256

×

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

×

=

=

(EQ 5)

I

LEDavg

30mA

256

5

1

+

(

) 256

×

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

×

5mA

=

=