Hi all, I have make a circuit need to use LM5122 for DCDC boost from Vin=15~21V to Vout=30V with 7A output, I just put those information to web bench design and generate the schematic to follow the component value as shown below:
Unfortunately, I have face problem:
1. At the beginning, I had found that more spike and noise at the output voltage especially when large load, make a fault trigger to the current sense so very early off the LM5122, after I add some ceramic cap. it's seems the noise is much smaller, but I don't know the problem is actually solved or not.
2. Since I am making a product which need to very lower power consumption in idle mode, so I will switch off the LM5122 when no use (by UVLO, or cut the Vin by external circuit), and wake up when some current drawing in the output. I have MCU to turn the LM5122 on if the current sense circuit have signal then trigger the MCU. If no current draw at start and wake up LM5122, everything is work fine. However, I observed when the current consume is larger when sleep, the LM5122 seems wouldn't wake up and the input is over current, it seems Cout need more power to charge up the capacitor but not success, then LM5122 is shut down, and wake up again and try to charge the capacitor....looping. Beside, M1 temperature is rising up. Where is the problem occur?
3. In previous talk, I need low power consumption in idle mode, I find that most current consume in sleep are Rfbt and Rfbb, leakage from the output, In addition to the LM5122 current is leakage even UVLO is off(so I cut the LM5122 Vin when the product sleep), I just attached my modification as below, is this reasonable? or any other issue need to pay attention?
Thanks so much for answer my question.