The reduction of output pulse-width accuracy has an even greater effect on the accuracy of power delivered to a resistive load since load power is proportional to the square of the current delivered.

LED power analysis taking the example of a resistive load scenario:

Equation 16.

Equation 17.

Equation 18.

Equation 19.

Equation 20.

Substituting input duty cycle from Equation 47,

Equation 21.

We can visualize the worst-case effects of pulse-width distortion on a resistive load scenario with the following conditions:

• HSS supply voltage: V_vs = 10 V
• Load resistance: R_load = 10 Ω
• PWM Duty Cycle: D_IN = 50%
• Pulse-width distortion: t_d(PWD) = ±50 μs (TPS4H000-Q1 min/max spec)

We can also quantify the variation of actual power dissipation due to compared to ideal.

Equation 22.

Using the example of TPS4H000-Q1,

• PWM Duty Cycle: D_IN = 50%
• Pulse-width distortion: t_d(PWD) = ±50 μs (TPS1H100 min/max spec)

We can see that if we consider a worst-case PWD scenario of TPS4H000-Q1, switching frequency is virtually limited to below 1 kHz again if relatively accurate load power is desired at 50% duty cycle. This figure is even lower if high accuracy is required at low duty cycles.

Figure 3-6 Potential Load Power Variation for TPS4H000, Normalized