RT6204 Design Guidelines and
Example Applications
RT6204 is a 60V, 0.5A Synchronous Buck converter, Richtek’s latest addition to the Wide Vin converter range. The 5.5V to 60V input range and 0.8V to 50V output range makes this IC suitable for a many different types of applications, and therefore the circuit design and key component selection can be slightly different from standard buck converter designs. Below are a few examples that highlight different design aspects of RT6204.
Generating auxiliary supplies in Photo Voltaic systems
Higher Power Photo Voltaic (Solar Power) systems often use higher DC bus voltages like 24V or 48V. Solar systems with maximum power point tracking may have considerable DC bus voltage fluctuations. This DC bus feeds the inverter and battery charger. These circuits often need well regulated lower auxiliary voltages for the charge control and inverter driver blocks.
RT6204 can provide well regulated auxiliary voltage from the fluctuating DC bus voltage. When high step-down ratio’s can happen, the converter minimum on time needs to be considered.
Two-stage high power LED driver system
High power LED driver systems often consist of a PFC flyback and a constant current buck LED driver at the secondary side. The PFC flyback delivers a secondary voltage which has some AC ripple. The buck LED driver provides a well regulated ripple free current for the LED string. These systems often need a dimming function, which requires an MCU and (RF) interface. RT6204 can be used to step-down the high LED driver supply voltage to a low 5V or 3.3V MCU supply. This has the advantage that only a single secondary winding is needed, and guarantees a stable MCU supply, even in low power standby mode when the LED driver is switched off. Maximum input supply rating and low power standby efficiency can be important factors in such a design. Read more for a reference design of the RT6204 in a 5V output application.
Voltage regulation from unregulated supplies
Quite a few industrial applications still use iron core transformers. The rectified output voltage of these supplies can vary considerably over mains voltage and load conditions.
RT6204 can be used to derive a well regulated supply voltage from the unregulated secondary voltage. When the unregulated input voltage minimum value comes close to the regulated 24V output voltage (like the above example where VIN min = 26.6V), the RT6204 maximum duty-cycle capabilities need to be carefully considered. The output capacitor choice for the 24V output supply may also be different from a normal low voltage supply. Read more for a reference design of the RT6204 in a 24V output application.
As can be seen from the above examples, a design with RT6204 can have different focus points, like high step-down ratio, maximum duty-cycle operation, different output capacitor types or low power efficiency.
The application note “RT6204 Wide Vin Buck Converter” examines 4 different converter designs: 1.2V output / 5V output / 12V output / 24V output. For each design, the wide input voltage range is considered and minimum and/or maximum duty-cycle conditions are analyzed in detail. Also the use of ceramic output capacitors vs. electrolytic output capacitors are compared and output ripple and converter stability aspects are examined.
Below schematic shows some of the key component calculation aspects for the RT6204 converter. Click the different blocks for more information on how to calculate these parameters.
For more information, please read the full application note ‘’ RT6204 Wide Vin Buck Converter’’.
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