ZHCSCK8H May 2014 – April 2025 LP8860-Q1
PRODUCTION DATA
In additional to conventional PWM dimming control the LP8860-Q1 supports Hybrid PWM and Current dimming. Hybrid dimming combines the PWM and current dimming methods. PWM dimming operates with a lower range of light, and linear current dimming is used with higher brightness values. If the <EN_PWM_I EEPROM> bit is set to 1, the system enables hybrid dimming. Principles of PWM dimming and Hybrid PWM and Current dimming are illustrated by Figure 6-7. Only 25% switch points and slope gain = 1 are shown for simplicity.
Figure 6-7 Principles of PWM Dimming and Hybrid PWM and Current DimmingLED forward voltage increases and efficiency declines when forward current is increased. Use of constant current with PWM dimming at lower brightness and current dimming at greater brightness (instead of PWM dimming at full brightness range), yields better optical efficiency and resolution especially at lower brightness values. The optimum switch point between PWM and current dimming modes and current slope depend on the LED type.
PWM control ranges from 12.5% to 50% and the current slope can be selected using <GAIN_CTRL[2:0]> and <I_SLOPE[2:0]> EEPROM bits, respectively (see Table 6-6 and Table 6-7).
Figure 6-8 Optical Efficiency Improvement With PWM and Current Dimming| GAIN_CTRL[2:0] | SWITCH POINT FROM PWM TO CURRENT DIMMING |
|---|---|
| 000 | 50.0% |
| 001 | 40.6% |
| 010 | 31.3% |
| 011 | 25.0% |
| 100 | 21.9% |
| 101 | 18.8% |
| 110 | 15.6% |
| 111 | 12.5% |
| I_SLOPE[2:0] | SLOPE GAIN |
|---|---|
| 000 | 1.000 |
| 001 | 1.023 |
| 010 | 1.047 |
| 011 | 1.070 |
| 100 | 1.094 |
| 101 | 1.117 |
| 110 | 1.141 |
| 111 | 1.164 |
The current setting for DISP_CL1_CURRENT[11:0] in Hybrid PWM and Current dimming mode can be defined by the following formula (assuming individual LED sink current correction DRV_OUTx_CORR[3:0] is 0%):

Example of calculation for Hybrid PWM and Current dimming mode, 100-mA maximum output current:
| Target maximum current 100 mA | IDISP_CL1_CURRENT = 100 – 100 × 1 × ((100 – 25) / 100) = 25 mA |
| Maximum scale 100 mA (DRV_LED_CURRENT_SCALE[2:0]=101) | |
| Slope = 1.000 (I_SLOPE[2:0]=000) | |
| Switch point = 25% (GAIN_CTRL[2:0]=011) |
Example of calculation for Hybrid PWM and Current dimming mode, 23-mA maximum output current:
| Target maximum current 23 mA | IDISP_CL1_CURRENT = 23 – 25 × 1.094 × ((100 – 25) / 100) = 2.49 mA |
| Maximum scale 25 mA (DRV_LED_CURRENT_SCALE[2:0]=000) | |
| Slope = 1.094 (I_SLOPE[2:0]=100) | |
| Switch point = 25% (GAIN_CTRL[2:0]=011) |