Datasheet LT8303 (Analog Devices) - 13

LT8303
applicaTions inForMaTion
VSW VSW VSW <150V <150V <150V VLEAKAGE VLEAKAGE VLEAKAGE <120V <120V <120V tOFF > 350ns tOFF > 350ns tOFF > 350ns tSP < 250ns tSP < 250ns tSP < 250ns TIME TIME TIME 8303 F05
No Snubber with DZ Snubber with RC Snubber Figure 5. Maximum Voltages for SW Pin Flyback Waveform
Lℓ Lℓ Z • C • • R • D 8303 F06
DZ Snubber RC Snubber Figure 6. Snubber Circuits
A snubber circuit is recommended for most applications. The Zener diode breakdown voltage should be chosen to Two types of snubber circuits shown in Figure 6 that can balance power loss and switch voltage protection. The best protect the internal power switch include the DZ (diode- compromise is to choose the largest voltage breakdown. Zener) snubber and the RC (resistor-capacitor) snubber. The Use the following equation to make the proper choice: DZ snubber ensures well defined and consistent clamping V voltage and has slightly higher power efficiency, while the ZENER(MAX) ≤ 150V – VIN(MAX) RC snubber quickly damps the voltage spike ringing and For an application with a maximum input voltage of 80V, provides better load regulation and EMI performance. choose a 62V Zener diode, the VZENER(MAX) of which is Figure 5 shows the flyback waveforms with the DZ and around 65V and below the 70V maximum. RC snubbers. The power loss in the clamp will determine the power rat- For the DZ snubber, proper care must be taken when ing of the Zener diode. Power loss in the clamp is highest choosing both the diode and the Zener diode. Schottky at maximum load and minimum input voltage. The switch diodes are typically the best choice, but some PN diodes current is highest at this point along with the energy stored can be used if they turn on fast enough to limit the leak- in the leakage inductance. A 0.5W Zener will satisfy most age inductance spike. Choose a diode that has a reverse- applications when the highest VZENER is chosen. voltage rating higher than the maximum SW pin voltage. 8303fa For more information www.linear.com/LT8303 13 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts