The LP5813 supports 8-bit PWM dimming with 24 kHz or 12 kHz frequency, which is configured by 'PWM_Fre' bit in Dev_config_1 register. An internal 6 MHz oscillator is used to generate the PWM clock. SYNC pin can be configured as PWM clock input or output by configure 'vsync_out_en' bit in Dev_Config_11 register. If multiple LP5813 are used in the system with autonomous animation engine control, all devices can refer the same clock signal, which comes from one of LP5813 or external controller, to avoid animation mismatch in long time operation.

Each LED can be configured into 3 different PWM alignment phases: Forward, Middle, and Backward. The alignment phase of each LED is set by 'phase_align' bits in Dev_Config_7 to Dev_Config_10 registers. By turning on the LEDs in different phase, the peak current load from boost or the system power supply is greatly decreased. The input current ripple and ceramic-capacitor audible ringing can also be reduced. Figure 9-14 shows the PWM alignment phases. In the forward alignment, the rising edge of PWM pulse is fixed at the beginning of PWM period. In the middle alignment, the middle point of PWM pulse is fixed at the middle of PWM period, while the pulse spreads to both directions. In the backward alignment, the falling edge of PWM pulse is fixed at the end of PWM period.

Figure 9-14 PWM Alignment Scheme

The LP5813 allow users to configure the dimming scale as exponential curve or linear curve, through the ‘exp_en’ bits in Dev_Config_5 and Dev_Config_6 registers. A human-eye-friendly visual performance can be achieved by using the internal exponential scale. The linear scale has great linearity between PWM duty cycle and PWM setting value, which provides flexible approach for external controlled gamma correction algorithm. The 8-bit linear and exponential curves are shown as Figure 9-15.

Figure 9-15 Linear and Exponential PWM Dimming Curves