Cirrus Logic AN368 - Manual (Page 10)

AN368
10 AN368REV2
3.2 Design Process
The design process requires a specification covering the required operating range, color temperature, dimmer
compatibility, form factor, and applicable standards. Once those specifications are defined, the recommended
design process is as follows:
Design the Flyback Stage
• Define power-stage components, such as the MOSFET and zener clamp, based on certain considerations,
including cost, performance, and space
• Calculate transformer parameters and remaining power-stage components
• Design transformer based on cost, size, and performance
• Design Synchronizer Circuit
• Specify protection thresholds
Design the Color System
Perform curve fit that meets target specifications for color and lumen output across the dimming range
Design the Boost Stage
• Pick power semiconductors for the boost stage based on input power required by flyback and nominal link
voltage
• Determine peak current in the boost stage during No-dimmer Mode
• Boost inductor design based on providing best-case tradeoff between efficiency, EMI, and size of
magnetics
Design of the Other Non-power Conversion Circuitry
• Design charge pump, auxiliary supply circuit for providing V
DD
to the IC
• Clamp circuit
Design the EMI Filter
• Design EMI filter to meet required compliance
Design Other Protections
• ZCD
• OCP, OLP, OVP, VDIFF, BOP, COP, LLP
• eOTP, iOTP
Layout the PCB
• Observe GND rules
• Sensitive traces
Optimize Output Regulation of Flyback Section
• Correct for actual ZCD offsets
• Compensate T2 commutation time
• I
PK(FB)
(T1) compensation
Program the Device
• OTP memory
• Compute CRC
• OTP Verification
Optimize EMI Filter
• Verify EMI filter meets dimmer compatibility
• Optimize EMI filter for compliance