Cirrus Logic AN372 - Manual (Page 5)

AN372
AN372REV1 5
3.2 Overview of Design Steps
The CS1612/13 LED driver IC controls a power converter system that has two distinct power-conversion
stages. The IC requires supporting circuitry to provide a steady-state power supply with gate bias, a clamp
circuit, and EMI filtering. The recommended design process is outlined below:
1. Start with the buck stage.
2. Design for full power at minimum V
BST
. Note that any design may require trade-offs for different operating
parameters.
3. Optimize the buck stage through validation and design iteration.
4. Base the boost stage design on the power requirement of the buck stage.
5. Start the boost stage design in No-dimmer Mode.
6. Determine the peak current in the boost inductor, I
PK(BST)
.
7. Determine a boost inductance, L
BST
, that adjusts the switching frequency within the defined range.
Consider the impact on the EMI.
8. Pick the boost FET based on peak current ratings.
9. Choose the power supply components.
10.Complete the non-power-converting circuitry: ZCD, OVP, eOTP, Clamp Circuit, Charge Pumps, and Bias
Circuits.
11. Design the EMI filter.
12.Lay out the PCB.
The buck stage design is carried out at the full brightness (full load) point. To achieve an optimal solution,
several iterations of the design process may be required. The EMI filter is particularly critical because there is
a small degree of freedom in selecting the EMI component values that meet the requirements below:
• Comply with EMI regulations
• Achieve compatibility with the largest variety of dimmers
• Smooth dimming, no flicker with a variable number of identical lamps controlled by one dimmer