Input Voltage: 23.5V to 32V with occasional transients to 42V
Nominal output voltage: 24V, dropout to 22V acceptable
Load: 0mA to 250mA
I have an application requiring an output with the conditions stated above. I am in the process of determining if the TPS54040A is an acceptable solution. I have a TPS54040EVM that I am using along with SwicherPro for my calculations. Below is my current circuit on the EVM.
These values are open to modification, although getting much larger input/output capacitance with 1206 and 1210 ceramics at 24V may prove difficult (extra capacitors can be added if needed). The capacitor values shown are nominal values and do not take into consideration DC bias effects.
I have a few questions/concerns.
What issues does the circuit have with DCM? Because my load gets very light, it simply is not possible to stay in CCM. If there are none I will likely lower my inductance. The recommended 30mA ripple will be hard with minimum input voltage (especially with a large inductor). Is 30mA always required, especially near dropout?
When my input voltage enters the dropout range I can audibly hear the inductor (with and without load, although the sounds are different). I assume this is from the pseudo-100% duty cycle during moderate to heavy load and ECO-Mode during light load. Or is this a stability issue? Will operation like this cause long-term issues?
VIN also has some minor ripple due to switch ringing. To prevent EMI/EMC issues, is it better to more heavily filter the input or use a snubber across D1 if overall efficiency isn't the biggest concern?
Is there a better solution or IC for this application? I have considered a SEPIC but have been wary about the increased complexity and stability issues.
Also, my load occasionally has self-contained PWM circuitry in the low kHz range. Will this cause any stability interactions with my control loop?
Thanks!