How to parallel TPS76901's

Do a search in this forum (Linear Regulators) for 'parallel ldo', you will get a number of hits.

See the following : Application Report SLVA250 "Ballast Resistors Allow Load Sharing Between Two Paralleled DC/DC Converters" Although written for two regulators, it can easily be scaled for more. http://www.ti.com/lit/an/slva250/slva250.pdf

Yeah, well, there are lots of references, but not really any solutions.  The ONLY reference that might be of value is the document.  Everything else is for high power and I'm under 200 mA @ 200C.

Sure, a switcher would be more available, but requires custom magnetics and many more components.  Not suitable for an MCM.

Hi Mike,

An ugly solution would be to use diodes to combine the two LDO outputs.  Schottky diodes would normally be good but they are too leaky for consideration at 200°C.  You could either live with the drop on a regular diode (much lower at 200°C) or put a diode in the LDO ground path to offset the output Voltage.  A resistor to leak a little more current into the ground path diode might be needed if the quiescent ground current from the LDO is too low to let the ground diode offset the series combining diode.

Best Wishes,

Andrew 

Hi Mike, or anyone else...any thoughts or comments on this proposed solution?

I doubt that the diodes will be the solution, and will certainly have higher losses than using the ballast resistor solution in the app-note. If you are using adjustable LDO's you could off-set the initial diode Vf by setting the output voltage a few hundred milli-volts higher. However, the LDO with the highest output voltage, even by a few milli-volts, will provide the bulk of the output current. That would make the diode on that output hotter, it's Vf would drop due to the heat, and the one LDO would try to provide even more current. Thermal run-away, of a sorts.

I was recently pointed to the datasheet for TPS7A45xx, "Figure 31. Paralleling Regulators for Higher Output Current"

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

No description in the application information on the circuit operation. Seems to be a variation of an article published ten years ago in Electronic Design (and that was probably borrowed from somewhere else) ...

http://electronicdesign.com/power/double-your-output-current-parallel-voltage-regulators

A master/slave arrangment where the two LDO input currents are compared and output voltage of the slave LDO is tweaked higher or lower.

The TPS7A45xx solution looks like it should be adaptable to any other regulator family with a programmable regulator.  Please forgive my asking, Mike: did you come across any HT alternatives to the TPS76901 other than the TPS7H1201-HT?