FEDEVEL
Platform forum

Oscar , 05-22-2018, 08:03 AM

Hi everyone,

I would like to ask for help in a technical doubt regarding Boost and LDO converters. Is it a good-practice design connect two LDO's at the output of the Boost converter. I need to get +-5V and +3.3V, with a max output current of 150mA for all of them. So I decided to use the TPS65131 boost converter from Texas Instruments, this Boost converter can provide two independet output voltages: one positive output voltage and one negative output voltage. However I need very low noise in the power rails, for that reason I am using ultra low noise LDO's at the positive output and at the negative output of the boost converter. So, the idea is get +-6V from the boost converter and then with one positive LDO, get +5V and with one negative LDO get -5V. I also want to connect other positive LDO at the +6V output to get 3.3V, but I do not know if this is a good practice, it means, connect two LDO´s at the output of one Boost converter. Thanks for help.

robertferanec , 05-23-2018, 12:00 PM

- I usually do not use LDO for bigger voltage difference. For example, if you will be making 3.3V from 6V, that is 2.7V (difference) * 150mA (if 3.3v has also 150mA max current) = 0.405W loss on the LDO regulator. Especially if you will be using boost converter, that may be a lot of wasted energy.

- Double check if the LDO will work ok with negative voltage and if you can use that output in your circuit

- What is the input voltage?

I would be also probably considering other options (maybe find a way using lower voltage, not 5V ?).

PS: Generally, if possible, I try to avoid using boost converter as they can be very noisy and may cause problems during EMC/EMI certification

robertferanec , 05-24-2018, 12:55 PM

There is no really recommended loss on LDO, However higher power = heat. Also, if this is a battery powered device, you may want to be very careful about wasted power losses.

I would have a look what other people are using in similar applications or if there are recommended chips / connections for these applications. I do not really know much about your application, so it is hard to suggest something.