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TPS723: DC DC Converter with LDOs(LP2992 & TPS723)

Part Number: TPS723
Other Parts Discussed in Thread: LP2992,

Hello together,

I am using two switching regulators in a parallel application to reduce the input voltage from 24V to ±3.3V. Then I connect the positive output +3.3V from the switching regulator to LDO LP2992. The negative output of -3.3V with LDO TPS723. At +3.3V the switching regulator has the output current of 500mA and at -3.3V the output current is -400mA. The wiring of the switching regulator is shown below.

Can LP2992 and TPS723 withstand these currents from the switching regulator?

What do I have to consider if I want to connect a switching regulator with linear regulators?

Kind Regards

Selvedin Hodzic

  • Hi Selvedin,

    I am not sure if I am understanding your question properly, but I will give it a shot.

    1. LDO's are commonly used to post regulate and filter output from a switching regulator. The key to making sure this works well is to have sufficient drop-put.  The wider the delta between VIN and VOUT, the better the PSRR (Power Supply Ripple Rejection). This is discussed in our LDO Basics VIdeo which can be viewed here. The below gif (if it comes through) shows why:

    2. I am not sure where figure 4 you posted above comes from, but there needs to be an inverting regulator to create the negative input to the negative LDO. For a negative LDO to work, the input voltage must have a lower potential than the output voltage as the negative LDO can only sink current. 

    3. LDO's typically have two means of self-protection. The first is an internal current limit and the second is a thermal shutdown threshold. This is really helpful if your input rail is powering several other subcircuits as the LDO well clamp the current or thermally shut down if there is a fault at the output without bringing down the whole system. 

    I hope this helps.