Checking Minimum LED Dimming Pulses Against Timing Resolution

A driver advertised with a large brightness register can still have practical limits at very low PWM duty cycles. The input decoder, output timing, and current rise time each affect the smallest useful light pulse. Review these separately before treating every numerical brightness step as a distinct optical level.

Identify the selected control mode

The TI LP8860-Q1 data sheet distinguishes decoded PWM duty control, register based brightness, and direct PWM operation. It also specifies input timing and timeout behavior. The applicable limitations depend on which mode is enabled.

Record input PWM frequency, internal dimming configuration, brightness scaling, and any hybrid mode. A control register with many bits does not automatically remove timing limits at the external input pin.

Calculate pulse duration

Multiply the PWM period by the smallest intended duty cycle. At a hypothetical 20 kHz input, the period is 50 microseconds; a 0.1 percent duty cycle produces a 50 ns high interval. Compare that duration with the selected device’s actual permitted input timing.

Check both high and low intervals. Near full brightness, the short interval may be the low time rather than the high time. Endpoint handling can also involve a timeout or special interpretation of a continuously high or low input.

Measure current pulse area

Capture LED current at the lowest intended commands. Inspect delay, rise, fall, plateau, and off current. The average current depends on the area under the waveform, so a narrow triangular pulse does not provide the same result as an ideal rectangular pulse of the same nominal width.

Compare adjacent commands and repeat several cycles. Quantization or jitter can make the average response uneven even when the control waveform changes in apparently uniform steps.

Verify usable brightness levels

Measure optical output with fixed geometry and appropriate integration time. Check monotonicity, repeatability, and any visible discontinuity when changing control modes. Include supply and temperature conditions that affect output headroom or current response.

Save timing settings, measured electrical pulse area, optical response, and the lowest accepted command. Define behavior for commands below that range, such as a documented off state or minimum level. A useful dimming specification states the verified usable range and update behavior. Quoting only register resolution or an ideal period divided by pulse width can overstate the number of distinct brightness levels available from the assembled LED system. Check that host timer rounding does not collapse several requested brightness values into the same physical pulse width.