One of the key features of the LMQ1 is slew-rate control. If the high-side top MOSFET turn-on time is too fast, there is a high overshoot in the switch-node voltage during this transition. When reducing the dead time for a synchronous buck, make sure that the high- and low-side MOSFETs never conduct at the same time.
Using slew-rate control optimizes the switch-node rise and fall time, eliminating switch-node ringing. The resistors I selected for this application are a good startup point for any application where the output power is under 50W. It also provided better control of the switch-node rise and fall and eliminated the need for a snubber circuit, which adds circuit complexity and cost.
By picking the correct values of slew-rate control resistors, not only can you reduce EMI; you can also improve system efficiency. You must Sign in or Register to post a comment.
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Your existing password has not been changed. Sorry, we could not verify that email address. An alternative to using the methods describe above to reduce switch-node ringing is to use the LMQ1 automotive-qualified synchronous buck controller.
One of the key features of the LMQ1 is slew-rate control. If the high-side top MOSFET turn-on time is too fast, there is a high overshoot in the switch-node voltage during this transition. When reducing the dead time for a synchronous buck, make sure that the high- and low-side MOSFETs never conduct at the same time.
Using slew-rate control optimizes the switch-node rise and fall time, eliminating switch-node ringing. The resistors I selected for this application are a good startup point for any application where the output power is under 50W. When the output is turned on, an inrush current flows to charge the capacitor connected to the load side. If this current is too large, the overcurrent protection circuit may malfunction, making it impossible to start up, or overshooting may occur in the output voltage.
To prevent this, this function limits the inrush current and controls the slew rate at the rise of the output voltage. The slew rate control function can control the rise of the output voltage with an external capacitor. The inside of the red frame in the left figure is the external capacitor CdVdT. By changing this value, the rising slew rate of the output voltage can be adjusted. The graph on the right shows the above relationship. The rush current can also be reduced by slowly rising this output voltage.
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