STMicroelectronics STLDC08 Demo Board STEVAL-ILL039V1/2 STEVAL-ILL039V1 STEVAL-ILL039V1 Fiche De Données
Codes de produits
STEVAL-ILL039V1
STLDC08
Detailed description
Doc ID 18476 Rev 1
15/29
7.5 Dimming
When PWMOUT goes to zero, the LED current immediately goes to zero and the energy
stored in the coil is discharged on the output capacitor, causing an increase in the output
voltage. As soon as the PWM goes back to high value, there is a big spike current on the
LED. This could damage the LED itself. To avoid this, as soon as the input PWM signal goes
to zero the controller immediately turns off the main switch (in order to discharge the coil
current on the LED branch). In this way the PWM power is turned off with a delay in order to
guarantee that FB goes high after PowerMOS turn off. After this delay, the flip-flop is ready
to be set and the PWM power is turned off. In this condition the output voltage is slightly
lower than the regulated value, but a current spike on the LED is avoided.
stored in the coil is discharged on the output capacitor, causing an increase in the output
voltage. As soon as the PWM goes back to high value, there is a big spike current on the
LED. This could damage the LED itself. To avoid this, as soon as the input PWM signal goes
to zero the controller immediately turns off the main switch (in order to discharge the coil
current on the LED branch). In this way the PWM power is turned off with a delay in order to
guarantee that FB goes high after PowerMOS turn off. After this delay, the flip-flop is ready
to be set and the PWM power is turned off. In this condition the output voltage is slightly
lower than the regulated value, but a current spike on the LED is avoided.