SNVSAE3B March 2016 – November 2017 LM5161
The LM5161 is designed to operate with an input power supply capable of supplying a voltage range between 4.5 V and 100 V. The power supply should be well regulated and capable of supplying sufficient current to the regulator during the sync buck mode or the isolated Fly-Buck mode of operation. As in all DC/DC applications, the power supply source impedance must be small compared to the converter input impedance in order to maintain the stability of the converter.
If the LM5161 is used in a buck topology with low input supply voltage (4.5 V) and large load current (1 A), it is prudent to add a large electrolytic capacitor, in parallel the CIN capacitors. The electrolytic capacitor stabilizes the input voltage to the IC and prevent droop or oscillation, over the entire load range. Also, it is necessary to add the electrolytic capacitor or a ceramic capacitor in series with appropriate ESR, parallel to the input capacitors CIN, in order to dampen the input voltage spikes, as detected by the LM5161 when connected to a power supply with long power leads. These input voltage spikes can easily be twice the input voltage step amplitude and a damping capacitor is necessary to contain the input voltage to less than 100V in order to protect the LM5161.