AS3661 datasheet(40/87 Pages) AMSCO

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AS3661

Datasheet - D e t a i l e d D e s c r i p t i o n

8.10.5 LEDx Control

These registers are used to assign the any current source output to the MASTER FADER group 1, 2, or 3, or none of

them. Also, the registers set the slope of the current sources output temperature compensation line and selects

between linear and logarithmic PWM brightness adjustment. By using logarithmic PWM-scale the visual effect looks

like linear. When the logarithmic adjustment is enabled, the chip handles internally PWM values with 12-bit resolution.

This allows very fine-grained PWM control at low PWM duty cycles. If a MASTER FADER is selected for an output, the

duty cycle on the output will be LED1 PWM register value (address 0x16) multiplied with the value in the MASTER

FADER register.

Besides the LED mapping and linear or logarithmic selection it is also possible to do a temperature compensation for

each output separately. The PWM duty cycle at temperature T (in centigrade) can be obtained as follows: PWMF =

[PWMS - (25 - T) * slope * PWMS] / 2, where PWMF is the final duty cycle at temperature T, PWMS is the set PWM duty

cycle (PWM duty cycle is set in registers 16H to 1EH) and the value of the correction factor is obtained from Table 8.

For example, if the set PWM duty cycle in register 16H is 90%, temperature T is -10°C and the chosen s lope is +1.5 1/

°C, the final duty cycle PWMF for LED1 output will be [90% - (25°C - (-10°C))* 1.5 1/°C * 90%]/2 = [90 % - 35 * 1.5 *

90%]/2 = 21.4%. Default setting 00000 means that the temperature compensation is non-active and the PWM output

(0 to 100%) is set solely by PWM registers LED1 PWM to LED9 PWM.

Table 14. LED1 CONTROL Register

LED1 CONTROL

Bit

Bit Name

Default

Access

Bit Description

7:6

LED1_MAPPING

R/W

This register defines the mapping of LED1 output to the master

faders. The faders can either be used for dimming several

LEDs in parallel or for ratiometric control of the output.

00: no master fader selected

01: MASTER FADER 1 controls LED1 output

10: MASTER FADER 2 controls LED1 output

11: MASTER FADER 3 controls LED1 output

LED1_LOG_EN

R/W

This bit is effective for both, program execution engine and

direct PWM control.

0: linear adjustment.

1: logarithmic adjustment.

4:0

LED1_TEMP_COMP

0 0000

R/W

The reference temperature is +25°C (i.e. the temper ature at

which all slope settings have no effect) and the temperature

coefficient (slope) can be set in 0.1 1/°C steps to any value

between -1.5 1/°C and +1.5 1/°C, with a default to 0.0 1/°C

11111: -1.5 1/°C

11110: -1.4 1/°C

...

00000: temperature compensation not activated

...

01110: +1.4 1/°C

01111: +1.5 1/°C

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