SNVA055I July 2002 – January 2022 LM2642
The evaluation board provides several optional component pads for flexibility in changing components.
For more information regarding device operation and component selection, see the LM26420/LM26420Q Dual 2.0A, High Frequency Synchronous Step-Down DC-DC Regulator Data Sheet.
In switching power supplies, the rapid increase of drain current in the top FET coupled with parasitic inductance generates unwanted LΔi/Δt noise spikes at the source node of the FET (SWx node) and VIN node.
The resistor in series with the SWx pin (R6, R11) slows down the gate drive (HDRVx), thus slowing the rise and fall time of the top FET, yielding a longer drain current transition time and reducing switch node ringing. Top FET switching losses will increase with higher resistance values. Small resistors (1 Ω–5 Ω) can also be placed in series with the CBOOTx pin (R7, R12). A CBOOT resistor will slow the rise time of the FET to reduce switch node ringing.
To maintain stable regulation, the FBx pins should remain free of noise. The LM2642 evaluation board has components C15 and C22 installed to suppress noise that may be picked up by the FBx traces. Notice that both of these capacitors are placed physically close to the FBx nodes. Pads C17 and C23 are provided for additional output capacitors.