This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS7A7002: Controlling more than one LDO output voltage with only one DAC

Part Number: TPS7A7002
Other Parts Discussed in Thread: DAC5311

Hi,

I found nice (with all equation) example of controlling LDO output voltage with DAC voltage...

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/give-your-voltage-regulator-the-margin-it-deserves

Is it possible that only one (the same DAC5311)  can be used to control more than one (exactly the same LDO's TPS7A7002) LDO's. For example one DAC with 3 LDO's with adjustable same (on all 3) output voltage?

  • Hello,

    I suppose in theory it would be possible to do this. The issue I'm seeing is that the errors in the feedback resistors for each of the 3 devices would all be different, and so you would not be able to use feedback from, for example, an ADC that is monitoring the output voltage of the LDO (if it were a single LDO), resulting in different output voltages for the devices. This is also assuming that the LDOs are configured for the same output voltage. If the LDOs were configured for different output voltages the problem becomes more complicated because now you have to worry about the range of each LDO for the same 0V to 5V (for example) DAC output and still account for the feedback resistor errors (not to mention the variation in VFB of each LDO when the LDO is loaded). 

    I think if you were to try simulating this it would probably work. In practice, though, I am not sure that you could reliably program all 3 LDOs to the voltages that you expect.

    Regards,

    Nick

  • Hi,

    In my setup there are will be more identical LDO's (on one PCB, one near another) with same power supply input voltage (input pins for regulators are tided together), and same output voltage level (output pins are not connected together, but to different devices that should work on the same voltage level). DAC is used only for voltage setup (once) and ADC is connected only to output of one regulator (and measuring voltage only during setup sequence, it is not automatic real-time follower / adjuster). Microcontroller take care about setup. Range will be 1.7V - 3.7V and small error of few mV is not a issue.

    I simply see DAC output pin as one voltage level, and I don't see influence of one current going over resistors from DAC output to LDO's ADJ/FB pin to current going over another resistors to another LDO's ADJ/FB pin. Again, I am aware of small voltage output difference, even LDO's will be from the same batch, and 0.1% resistors will be precisely measured to identical as posible values. 

  • Hello,

    I agree that the DAC output will be a single voltage and the feedback from each LDO should not interfere with each other much (except maybe during a large transient in one of the devices where the VFB changes). In the case that the LDOs are all the same device, they all have the same nominal output voltage, and you can tolerate some output voltage deviation, I think this will be fine. The only thing you will need to be sure of is that your DAC output can source enough current for all 3 feedback networks. 

    Regards,

    Nick