AS3689 datasheet(44/72 Pages) AMSOSRAM

44 / 72 page

AS3689

austriami crosyst ems

Datasheet, Confidential

www.austriamicrosystems.com (mlg, ptr)

Revision 1.0.2 / 20070115

42 - 70

7.4.8 PWM Generator

The PWM generator can be used for any current sink (CURR1, CURR2, CURR3x, CURR4x, CURR5x, CURR6,

RGBx).. It can be programmed to use the pin GPIO (pwm_mode=0) or an internal PWM generator

(pwm_mode=1). The setting applies for all current sinks, which are controlled by the pwm generator (e.g.

CURR1 is pwm controlled if curr1_mode = 10, RGB1 is pwm controlled if rgb1_mode = 10). The pwm modulated

signal (internal / external) can switch on/off the current sinks and therefore depending on its duty cycle change

the brightness of an attached LED.

7.4.8.1 Internal PWM Generator

The internal PWM generator uses the 2MHz internal clock as input frequency and its dimming range is 6 bits

digital (2MHz / 2^6 = 31.3kHz pwm frequency) and 2 bits analog. Depending on the actual code in the register

‘pwm_code’ the following algorithm is used:

If pwm_code bit 7 = 1

Then the upper 6 bits (Bits 7:2) of pwm_code are used for the 6 bits PWM generation, which controls the

selected currents sinks directly

If pwm_code bit 7 =0 and bit 6 = 1

Then bits 6:1 of pwm_code are used for the 6 bits PWM generation. This signal controls the selected current

sinks, but the analog current of these sinks is divided by 2

If pwm_code bit 7 and bit 6 = 0

Then bits 5:0 of pwm_code are used for the 6 bits PWM generation. This signal controls the selected current

sinks, but the analog current of these sinks is divided by 4

Figure 24 – PWM Control

pwm_code

7 6 5 4 3 2 1 0

6 bit PWM

to current sink(s)

6 bit PWM

to current sink(s) but analog

currents are divided by 2

6 bit PWM

to current sink(s) but analog

currents are divided by 4

0 0

AS3689 Datasheet(PDF) 44 Page - ams-OSRAM AG