The following equations provide a guideline to calculate the required parameters for the design configuration.

The first step is to calculate the required energy which needs to be stored in the buffer capacitor for a single LED pulse with Equation 1.

where

• V_F(MAX) is the maximum forward voltage of one IR LED
• I_LED is the desired peak LED current
• N is the number of LEDs connected in series
• t_ON is the desired LED current pulse on-time
• η is the estimated efficiency of the LED driver

In the next step, the required high-side switch current limit can be calculated with Equation 2.

where

• V_Boost is the configured output voltage of the boost converter stage
• t_off specificies the time for recharging the buffer capacitor and can be selected depending on the LED pulse frequency and on-time

The calculated value represents the minimum recharge current which is required to fully recharge the buffer capacitor before the next LED pulse occurs.

Once an appropiate recharge current has been selected, the resulting input current which flows over the coaxial cable and PoC filter inductors can be determined with Equation 3.

where

• I_LIM is the selected recharge current limit
• V_PoC is the voltage on the coaxial cable
• η is the estimated efficiency of the boost converter
• ΔI is the peak-to-peak inductor ripple current, which is typically 20 - 40 % of the output current

In the last step, the required buffer capacitor size can be calculated with Equation 4.

V_BUF(MIN) represents the minimum voltage level in the buffer capacitor at the end of the discharge cycle. The minimum voltage level must be greater than the maximum expected output voltage of the LED driver.