Other Parts Discussed in Thread: LM2841
This design started out with an LM2841, but due to increases in the current draw in SD cards it was necessary to switch to the 600mA LM2842X After using the online tools to calculate input/output caps, diode, and inductor, the results are an unstable switching output that results in the needed 3.3V output (with large ripple).. It is running at the 550KHz frequency, but in between the 550KHz switching times, there are 3 additional switch events that occur on the output. The output will not even support 50mA in this condition. Here are the values being used:
VIN = 24V nom
CIN = 2.2uf Tantalum along with a 100uF electrolytic
COUT = 47uF X7R
IIND = 47uH shielded ferrite.
Using an inductor value of 100uH impoved bud did not eliminate the oscillation.
Beyond upping capacitance and inductance, is there an alternate method to help stabilize the circuit.
One thought was to use a feed forward cap on the upper feedback resistor/divider. Please not that this PCB has worked perfectly for years using the LM2841.
Thoughts?
