LM2990: Can I parallel up multiple devices to increase current capability?

Hello,

Please see the resources at the bottom of this reply. There is a lot of information here so please reply back if you have any questions.  The excel calculator will help you a lot, there is no VBA in it so you should be able to download it without any issues.  We can also help design this for you if you prefer, as long as you give us some additional requirement information (see below).

LM2990

You can parallel any LDO using ballast resistors, thus it is also possible to parallel multiple LM2990 LDO's. The main drawback of this device is the inability to connect the references together of multiple LM2990.  Thus the error voltage (that is, the difference between each LDO output voltage in the parallel LDO system) can be high.  Assuming each LDO is the same temperature, we can approximate the error as +/- 100 mV for the -5V and -5.2V output option, +/- 240 mV for the -12V option, and +/- 300 mV for the -15V option.  This will lead to larger values of ballast resistance required and possibly more LDOs than 2 in parallel to meet other requirements (such as output voltage tolerance).  Even still, it is certainly possible and we can help provide ballast resistor values if you would like.  I will need the answers to the following requirements:

Ambient Temperature
Maximum junction temperature per LDO [optional]
Input Voltage
Output Voltage and output voltage tolerance
System Noise Requirement [optional]
Maximum output current

TPS7A33

A more modern solution that most customers parallel is the TPS7A33 and this is the path I would recommend if possible.  The TPS7A33 is almost 12 years newer than the LM2990 and includes design improvements as well as the ability to connect the references together.  You will likely have a smaller solution with the TPS7A33.  The TPS7A33 is already in the simple calculator (see the link below).  You can either fill out the calculator yourself or you can answer the same questions above and I can quickly provide you the results.

Thanks,

Stephen

Simple calculator for complex parallel LDOs
PARALLEL-LDO-CALC [NEW]

New, comprehensive design resources are available for paralleling LDOs using ballast resistors. 

A Scaleable, High-Current, Low-Noise Parallel LDO Reference Design [NEW]
Comprehensive Analysis and Universal Equations for Parallel LDO's Using Ballast Resistors [NEW]
Parallel LDO Architecture Design Using Ballast Resistors [NEW]