The LP5862 device uses time-multiplexing matrix
scheme to support up to 36 LED dots with a single chip. The device integrates 18
current sinks with 2 scan lines to drive 18 × 2 = 36 LED dots or 6 × 2 = 12 RGB
pixels. In matrix control scheme, the device scans from Line 0 to Line 1
sequentially as shown in Figure 8-1. Current gain and PWM duty registers are programmable for each LED dot to support
individual analog and PWM dimming.
Figure 8-1 Scan Line Control
Scheme
There are two high-side p-channel MOSFETs (PMOS)
integrated in LP5862 device. Users can flexibly set the active scan numbers from 1
to 2 by configuring the 'Max_Line_Num' in Dev_initial register. The
time-multiplexing matrix timing sequence follows the Figure 8-2.
tPWM is the current
sink active time, which equals to 8 us (PWM frequency set at 125 kHz) or 16 us
(PWM frequency set at 62.5 kHz) by configuring 'PWM_Fre' in Dev_initial
register.
tSW_BLK is the switch
blank time, which equals to 1 us or 0.5 us by configuring 'SW_BLK' in
Dev_config1 register.
tphase_shift is the PWM phase shift
time, which equals to 0 or 125 ns by configuring 'PWM_Phase_Shift' in
Dev_config1 register.
Total display time for one complete
sub-period is tsub_period and it can be calculated by the following
equation:
Scan_line# is the scan line
number determined by 'Max_Line_Num' in Dev_initial register.
The time-multiplexing matrix scheme
time diagram is shown in Figure 8-3. The tCS_ON_Shift is the current sink turning on shift by configuring
'CS_ON_Shift' bit in Dev_config1 register.
The LP5862 device implements
deghosting and low brightness compensation to remove the side effects of matrix
topology:
Deghosting: both upside deghosting and
downside deghosting are implemented to eliminate the LED's unexpected weak
turn-on.
Upside_deghosting:
discharge each scan line during its off state. By configuring the
'Up_Deghost' in Dev_config3 register, the LP5862 discharges and
clamps the scan line switch to a certain voltage.
Downside_deghosting:
pre-charge each current sink voltage during its off state. The
deghosting capability can be adjusted through the 'Down_Deghost' in
Dev_config3 register.
Low Brightness Compensation: three groups
compensation are implemented to overcome the color-shift and non-uniformity
in low brightness conditions. The compensation capability can be through
'Comp_Group1', 'Comp_Group2', and 'Comp_Group3' in Dev_config2 register.