There are several methods to control the PWM duty cycle of each LED dot.

• Individual 8-bit / 16-bit PWM for Each LED Dot

  Every LED has an individual 8-bit or 16-bit PWM register that is used to change the LED brightness by PWM duty. The LP5862 uses an enhanced spectrum PWM (ES-PWM) algorithm to achieve 16-bit depth with high refresh rate and this can avoid flicker under high speed camera. Comparing with conventional 8-bit PWM, 16-bit PWM can help to achieve ultimate high dimming resolution in LED animation applications.

• 3 Programmable Groups of 8-bit PWM Dimming

  The group PWM Control is used to select LEDs into 1 to 3 groups where each group has a separate register for duty cycle control. Every LED has 2-bit selection in LED_DOT_GROUP Registers (x = 0, 1, … , 9) to select whether it belongs to one of the three groups or not:

  • 00: not a member of any group
  • 01: member of group 1
  • 10: member of group 2
  • 11: member of group 3

• 8-bit PWM for Global Dimming

  The Global PWM Control function affects all LEDs simultaneously.

The final PWM duty cycle can be calculated as below:

The LP5862 supports 125-kHz or 62.5-kHz PWM output frequency. The PWM frequency is selected by configuring the 'PWM_Fre' in Dev_initial register. An internal 32-MHz oscillator is used for generating PWM outputs. The oscillator’s high accuracy design (ƒ_{OSC_ERR} ≤ ± 2%) enables a better synchronization if multiple LP5862 devices are connected together.

A PWM phase-shifting scheme is implemented in each current sink to avoid the current overshot when turning on simultaneously. As the LED drivers are not activated simultaneously, the peak load current from the pre-stage power supply is significantly decreased. This scheme also reduces input-current ripple and ceramic-capacitor audible ringing. LED drivers are grouped into three different phases. By configuring the 'PWM_Phase_Shift' in Dev_config1 register, which is default off, the LP5862 supports t_{phase_shift} = 125-ns shifting time shown in Figure 8-4.

• Phase 1: CS0, CS3, CS6, CS9, CS12, CS15
• Phase 2: CS1, CS4, CS7, CS10, CS13, CS16
• Phase 3: CS2, CS5, CS8, CS11, CS14, CS17

To avoid high current sinks output ripple during line switching, current sinks can be configured to turn on with 1 clock delay (62.5 ns or 31.25 ns according to the PWM frequency) after lines turn on, as shown in Figure 8-3. This function an be configured by 'CS_ON_Shift' in Dev_config1 register.

The LP5862 allows users to configure the dimming scale either exponentially (Gamma Correction) or linearly through the 'PWM_Scale_Mode' in Dev_config1 register. If a human-eye-friendly dimming curve is desired, using the internal fixed exponential scale is an easy approach. If a special dimming curve is desired, using the linear scale with software correction is recommended. The LP5862 supports both linear and exponential dimming curves under 8-bit and 16-bit PWM depth. Figure 8-5 is an example of 8-bit PWM depth.

In summary, the PWM control method is illustrated as Figure 8-6: