8.3.2.8 Phase Shift PWM Scheme

Phase shift PWM scheme allows delaying the time when each LED driver is active. When the LED drivers are not activated simultaneously, the peak load current from the boost output is greatly decreased. This reduces the ripple seen on the boost output and allows smaller output capacitors. Reduced ripple also reduces the output ceramic capacitor audible ringing. PSPWM scheme also increases the load frequency seen on the boost output six times and therefore transfers the possible audible noise to the frequencies outside of the audible range.

Description of the PSPWM mode is seen inTable 6. PSPWM mode is set with <PS_MODE[2:0]> bits.

Table 6. LED String Configuration

PS_MODE[2:0]	WAVEFORMS	CONNECTION
000
	6 LED strings with 60 degree phase shift. One driver for each LED string.
001
	5 LED strings with 72 degree phase shift. One driver for each LED string. (Driver #6 not used).
010
	4 LED strings with 90 degree phase shift. One driver for each LED string. (Drivers #5 and #6 not used).
011
	3 LED strings with 120 degree phase shift. One driver for each LED string. (Drivers #4, #5 and #6 not used).
100
	2 LED strings with 180 degree phase shift. One driver for each LED string. (Drivers #3, #4, #5 and #6 not used).
101
	3 LED strings with 120 degree phase shift. Two drivers for each LED string. (Drivers 1&2, 3&4 and 5&6 are tied and with the same phase).
110
	2 LED strings with 180 degree phase shift. Three divers for each LED string. (Drivers 1&2&3 and 4&5&6 are tied and with the same phase).
111
	1 LED string driven by all six drivers. (All drivers are tied and with the same phase).