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Table 8-3. Individual 8-bit Dot Current (DC) Setting (continued)

8-BIT DC REGISTER

RATIO OF OUTPUT CURRENT TO IOUT_MAX × CC/127

Binary

Decimal

- - -

1000 0000 (Default)

128 (Default)

50.2 (Default)

- - -

1111 1101

253

99.2

1111 1110

254

99.6

1111 1111

255

100

In summary, the current gain of each current sink can be calculated as below:

IOUT (mA) = IOUT_MAX × (CC/127) × (DC/255)

(3)

For time-multiplexing scan scheme, if the scan number is N, each LED dot's average current IAVG is shown as

below:

IAVG (mA) = IOUT/N = IOUT_MAX × (CC/127) × (DC/255)/N

(4)

8.3.3 PWM Dimming

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 LP5860T uses an enhanced spectrum PWM (ES-PWM) algoithm 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 while each group has a separate register

for PWM control. Every LED has 2-bit selection in LED_DOT_GROUP Registers (x = 0, 1, … , 54) to select

whether the LED dot 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:

PWM_Final(8-bit) = PWM_Individual(8-bit) × PWM_Group(8-bit) × PWM_ Global(8-bit)

(5)

PWM_Final(16-bit) = PWM_Individual(16-bit) × PWM_Group(8-bit) × PWM_ Global(8-bit)

(6)

The LP5860T 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 31.2-MHz oscillator is used for generating PWM

outputs. The oscillator’s high accuracy design (ƒOSC_ERR ≤ ± 3%) enables a better synchronization if multiple

LP5860T 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

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LP5860T

SNVSCE1 – MAY 2023

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