LP5907 – About parallel operation of this device

I'm surprised that no one has posted here yet. This is usually an easy answer.

" .... Can you recommend the following figure? ..."

In short ... No.

Direct connection of the two outputs causes the LDO with highest ouput voltage, even if only a few milli-volts higher, to supply the majority of the current. In this method, current sharing between the two LDOs is usually around 90%/10%, but a lot depends on device load regulation, output voltage matching, and juction temperature matching.

Adding ballast resistors at the outputs is an option, but at this current level it is not a very attractive solution as load regulation usually suffers. But current sharing could get as good as 60%/40% 

http://www.ti.com/lit/an/slva250/slva250.pdf

Active balancing is NOT an option here, at it requires at least one of the two LDOs to be an adjustable, plus a handful of other components, See Figure 35 (Page 21) in the TPS7A45xx datasheet for an example. Note that one LDO is fixed, the other is ADJ.in this example.

http://www.ti.com/lit/ds/symlink/tps7a4501.pdf

Also, you can search for the word 'parallel' in the Linear Regulator forum for numerous other discussions on this topic.

Hi Donald-san,

I apologize for the late reply.

Thank you for the information!

I understood that our customer has to connect the ballast resistors to perform the current sharing.

And, I refer to the following thread.

http://e2e.ti.com/support/power_management/linear_regulators/f/321/t/159076.aspx?pi300775=1

Based on this thread, I calculated the ballast resistors value.

LP5907 output accuracy is 4.5V +/- 2% (4.59V(max), 4.41V(min)).

And, the Load current is 300mA.

If the targeted load voltage is 4.4V, then

Rballast1=((4.41V-4.4V)/(300mA/2))=10mV/150mA≒66mohm

Rballast2=((4.59V-4.4V)/(300mA/2))=190mV/150mA≒1266mohm

Is my understanding incorrect?

Could you please review this and let me know if you have any advice?

Regards,

Kanemaru

Yes, your understanding is correct ONLY IF you know the exact Vout value for each LP5907 that is sharing current. Then you can hand calculate and select the closest R values.

If you do NOT know the exact Vout for each LP5907 then you will need to use more generic calculations, and be prepared for the real possibility of imperfect current sharing and not meeting the target load voltage of 4.40V @ 300mA load current.