Part Number:TPS7A85A
Tool/software:TINA-TI or Spice Models
Hello,
I need a LDO regulator that can provide Vin = 3.3V, Vout = 1.0V and capable of sourcing up to 8A, and upon searching, I found TPS7A85A to be the best candidate. To achieve this high of a current output, it would mean I would need qty 3 TPS7A85A LDOs in parallel. After researching current sharing and LDOs in parallel, TI mentioned that for high current and low noise TIDA-01232 (ballast resistors) should be used, and for high accuracy TIDU142 (control loop and sense resistors) should be used. I am leaning towards using the TIDA-01232 design, due to the fact it has been thoroughly tested with six LDOs in parallel and specifically uses the TPS7A85A; while the TIDU421 design has only been tested with two LDOs and used a different LDO part.
1) If high accuracy is the requirement, is it recommended to use TIDU421 design with qty three TPS7A85A in parallel or is it strictly for only two LDOs? If three is acceptable, how would that be implemented? Would a double supply control loop op amp be needed?
2) I have simulated the TIDA-01232 design in Tina with 3 LDOs in parallel, and wanted to clarify the RBallast and Evout (see calculations below):
In the reference design, there is a given Evout formula, in which I calculated assuming Voutnom = 1V and ERfb = 1% (not sure about this value since it wasn't given or if its needed?)
However, in the document it also mentions using Evout = 0.75mV.
I am unsure if I should use the Evout I calculated or the 0.75mV mentioned below.
Next, I calculated RBallast using the given formula below. However, I am unsure if this formula is specifically for 2 LDOs in Parallel or if can be used for multiple. If its for multiple then shouldn't the "2" multiplied with IoutMaxSingle be "n", the number of LDOs in parallel? If it is just "2" then I would get a negative result for Rballast.
Note: I Used 0.75mV for Evout for the Rballast calculations because I wasn't sure if I should use the calculated 14mV.
Simulation: Looking at the transient result, it seems like the schematic is designed correctly. I achieved an output voltage of 993.63mV. But would like to know if there are more ways to improve the accuracy of my schematic. Also, is the current going through the ballast resistors supposed to be so small? (probed it with the DMM and current = 5nA for the three ballast resistors)
