AN4460 datasheet(23/54 Pages) STMICROELECTRONICS

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AN4460

Firmware implementation

interrupt is received when the next dimming even is required, as specified in the

onoff[][] structure.

When the interrupt routine sets a SMED ON, the startup flag for the ADC delayed

acquisition (using the AWU peripheral) is also set.



SMEDx_ISR(): SMED interrupt

The interrupt is used to stop the SMED when an OCP problem is detected. The

interrupt is generated by a SMED on exit from S3. The SMED is in S3 only if

event(1) is received during S1. The interrupt routines stop the SMED by changing

the SWx bit and giving the fault signal to the main function, which turns on the red

“fault” LED. The SMED is reactivated on its next dimming cycle and if the OCP

problem is not removed then the SMED evolves into S3, triggering the

SMEDx_ISR interrupt again.

Auto-wakeup unit. The auto-wakeup unit is used while the CPU waits for the

current startup and LED voltage settlement time before starting the ADC

acquisition. For a correct FOT implementation the ADC measures the VCOMx

voltage when the PWM is ON and when the VLED has a correct value. This time is

fixed to around 100 µs after the SMED start. When the AWU time expires, the

interrupt starts the ADC channel acquisition.



ADC_ISR(): ADC interrupt

The routine samples, for each channel, VLED_PW and VCOMx, 4 times respectively.

The values are then averaged and stored. The ADC sampling routine occurs 100

µs after the start of the PWM dimming. Should the PWM dimming time be smaller

than 100 µs, the ADC samples incorrect voltage values and therefore the samples

are discarded. This protection (inconsistent voltage protection) is implemented via

the SMED_Active bit.

The interrupt routine uses the adc_eoc flag to inform the main function that the

ADC operation is completed and that new data is available. As a consequence,

the software discards the ADC value. The interrupt routine uses the adc_eoc flag

to inform the main function that the ADC operation is completed and that new data

is available.



Get_Key()

This routine is used to detect if the board buttons are pressed. The STLUX385A

uses the ADC (ADCIN[7], pin 31) to sense the button status. Since the ADC is

used also to read VCOMx and VPWR, a protection is set to avoid conflicts.



Comp_PWM()

It computes the new SMED’s operating parameters as calculated by the adaptive

voltage compensation mechanism.The new values are updated on the SMED

registers only during the next STOP phases (using the upd_flags variable with

UPD_PWMx flags).



Comp_DUTY()

This routine is invoked when the user changes the dimming period. The routine

computes a new dimming period based on the ontime[] structures and stores

the result on tmp_onoff[][] structures. The update is performed at the

beginning of the next dimming period (using the upd_flags variable with

UPD_DUTY flags) and when the dimming is OFF. During the update, the

tmp_off[][] structure is copied into the onoff[][] structure.

The tasks displayed in the previous picture refer to the PWM and dimming control

operations only. The STLUX385A firmware handles other tasks such as the command line,

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