DC/DC Converter Flexibility Enables Adding Noise Reduction Circuitry In this short video, I’ll discuss two simple noise reductions techniques that you can easily implement with a discrete DC/DC converter. But, if you’re using an integrated power module, these options are not available.

Integrated power module vs. discrete DC/DC converter Slide 2 - 1 When starting your power design, you can either choose an integrated module or discrete converter. Power modules are attractive solutions because they’re easy to use and don’t require you to select external components such as: The compensation network Output inductor Boot capacitor Plus other components not show in the diagram on the left. Due to the integration of these components in a power module it is much easier to create a DC/DC converter solution that will enable shortened design time which enables a quicker time to market Slide 2 -2 Discrete DC/DC converters on the other hand are little more complicated to implement, but this added complexity allows you to add external circuitry like a boot resistor and Snubber network that will help reduce the radiated and conducted noise. Also with the external compensation you will have more flexibility to add a secondary pie filter for additional noise reduction. I will show the advantages of adding the boot resistor and Snubber network in the following slides

DC/DC converter comparison without & with noise reduction circuitry Slide 3 - 1 The diagram on the left shows the simplified schematic for a discrete DC/DC converter. For this example we used the TPS54824 DC/DC converter that has fixed frequency operation with external compensation. The TPS54824 in this configuration will provide similar performance a fully integrated power module   Slide 3 – 2 Now in the diagram on the right you can see the simplified schematic with the addition of a 3ohm resistor in series with the Boot capacitor and RC Snubber network with a 5ohm resistor plus a 330pF capacitor. With these additions we able to reduce both the switch node ringing and peak to peak output ripple which in turn will reduce the overall conducted and radiated EMI. Since we used 0603 package size for all three components there is very little impact on the total solutions size

Switch node ringing Switch Node: 10V/div 10ns/div Switch Node: 10V/div Without Boot Resistor and Snubber RC With Resistor and Snubber RC ~17V peak ~14V peak Switch Node: 10V/div 10ns/div Switch Node: 10V/div 10ns/div The scope plot on the left highlights the switch node ringing of the DC/DC converter without the extra 3ohm boot resistor and 5ohm resistor plus a 330pF capacitor in the RC snubber network. The scope plot on the right highlights the switch node ringing of the DC/DC converter with the extra 3ohm boot resistor and 5ohm resistor plus a 330pF capacitor in the RC snubber network. You will notice that the addition of the extra boot resistor and RC Snubber network the peak switch node voltage is reduced from approximately 17 volts to 14V which is a reduction of 3V.

VOUT ripple VOUT 5mV/div 400ns/div VOUT 5mV/div 400ns/div Without Boot Resistor and Snubber RC With Resistor and Snubber RC ~40mV peak to peak ~15mV peak to peak VOUT 5mV/div 400ns/div VOUT 5mV/div 400ns/div The scope plot on the left highlights the output voltage ripple of the DC/DC converter without the extra 3ohm boot resistor and 5ohm resistor plus a 330pF capacitor in the RC snubber network. The scope plot on the right highlights the output voltage ripple of the DC/DC converter with the extra 3ohm boot resistor and 5ohm resistor plus a 330pF capacitor in the RC snubber network. You will notice that the addition of the extra boot resistor and RC Snubber network the output voltage ripple is reduced from approximately 40mV peak to peak to approximately 15mV which is a reduction of 25mV.

Efficiency comparison Without Noise Reduction With Noise Reduction Now you would think that by adding both the extra 3ohm boot resistor and the RC Snubber network with a 5ohm resistor plus a 330pF capacitor the overall efficiency would be greatly affected but as you can see in the efficiency plot we observed minimal decrease in overall efficiency a full load current of 8A

Summary Modules are simple to design with but Discrete DC/DC converters enable the addition of simple circuits to help reduce noise in your system Snubber Circuit 1 - 5W 0603 resistor and 1 - 330pF 0603 Capacitor Boot Resistor 1 - 3W 0603 resistor Small impact on overall solution size Decreased the switch node ringing amplitude by 3 volts from ~17V peak to ~14V peak Decreased the VOUT ripple from ~40mV peak to peak to ~15mV peak to peak Small impact on the overall circuit Efficiency