SLUU130A – September 2002 – Revised February 2003
Figure 2 shows the plots for the closed loop gain and phase with VIN = 3.3 V and IOUT = 4.4 A. At the crossover frequency of 60 kHz the phase margin is approximately 51 degrees.
GAIN AND PHASE MARGIN
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| 40 |
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| ILOAD = 4.4 A |
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| VI = 3.3 V |
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Frequency – Hz
Figure 2.
4.8Snubber Component Selection
The switch node where Q1 and L1 come together is very noisy. An
As a starting point, the snubber capacitor, C9, is generally chosen to be 5 to 8 times larger than the parasitic capacitance at the node, which is primarily COS of Q1:B. Since COS is 440 pF for Q1:B, C9 is chosen to be 3.3 nF. R3 is empirically determined to be 2.2 Ω , which minimizes the ringing and overshoot at the switch node. With low input voltages the power loss, 1/2⋅ C⋅ V2⋅ f , is relatively small at 24 mW.
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