needed, then Overlap1 and/or Overlap2 bits are written to

‘1’. Switch enable bits G1SW, R1SW and B1SW bits need to

be written to ‘1’ if corresponding RGB1 output is to be

activated. The switch enable bits G2SW, R2SW and B2SW

have same effect to RGB2 outputs. Switch enable bits have

effect only in overlapping mode.

Following chapters describe RGB functionality and modes in

more details.

MODES OF OPERATION

Constant Current/Switch Mode

The LEDs are driven either by constant current sink or

switches.

By using constant current mode the LED current is limited

based on external resistors Rr, Rg and Rb connected to pins

IR, IG and IB. Only one RGB LED per output is recom-

mended in this mode.

The LED currents can be adjusted with resistors based on

the following table.

RR or RG or RB

[

Ω]

Typical I

LED

[mA]

5.6k

22.0

6.8k

18.1

8.2k

15.0

10k

12.3

12k

10.3

15k

8.2

18k

6.8

The switch mode uses constant current mirrors as low ohmic

switches. Switch mode requires an external ballast resistor

to limit the LED current. This mode is used if 2 or more RGBs

are connected in parallel. To prevent the current variation

due output voltage accuracy it is recommended to use

charge pump in double (2x) mode.

The mode selection is shown on the following table.

CC/SW(1/2)

Mode

Comment

0

Constant Current Mode

LEDs are driven with constant current sinks. Maximum current is limited by Rr,

Rg and Rb

1

Switch Mode

LEDs are driven with switches. Maximum current is limited by ballast resistors.

Overlapping/Non-Overlapping Mode

This mode control defines how the RGBs are controlled by

PWM timing logic. Overlapping mode turns on and off the

RGBs at the same time. Non-overlapping mode splits the R,

G and B to phases based on selected color and thus limits

the maximum output current through the RGB LED.

The selection for this mode is as follows.

Overlap(1/2)

Mode

Comment

0

Non-overlapping Mode

LEDs are driven with non-overlapping method to minimize the noise and

current consumption. Frame based color control is enabled.

1

Overlapping Mode

LEDs are driven with overlapping method. Maximum current consumption is

6*Imax. Color control is disabled.

Overlapping Mode

Since RGB outputs are on simultaneously, the maximum

load peak current is

I

I(G2)

Overlapping Mode Timing Diagram

The brightness is controlled using PWM duty cycle based

control method as the following figure shows.

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