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TPS60400 - problem getting -5V for

elbert shiang
Prodigy 10 points
Other Parts Discussed in Thread: TPS60400, ADS1299, TPS60403

Hi, I have a filter circuit that uses opamps, the problem is that opamps require -5V,

 I've used a charge pump TPS60400 to helo get me a -5V supply, but instead of giving me -Vin which would be equal to -5V it's giving me only -1.4V, which is too little. Anyone have an idea on how to get a proper -5V supply.

  • 0
    TI__Guru*** 142860 points

    The TPS60400 can indeed do this for you if your load current is small enough and the circuit is designed properly.  How much current does your -5V rail take?  You can use a lab supply to give it -5V and measure the current used.

    There is an EVM available for the TPS60400, so you could order that and test your circuit with a known good TPS60400 design.  Could you post your schematic?

    Where are you measuring the output voltage?  Could you measure Vin also?

  • 0 in reply to Chris Glaser
    TI__Guru*** 142860 points

    Were you able to solve your issue?  If so, please post your solution so that everyone may learn.

  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Hi, I am developing my own acquisition board based on ADS1299. The idea is to use it with a Tiva Launchpad board. ADS1299 acquire, convert and send to the Tiva by SPI, the Tiva receive data and send them to PC by USB. I tried the system before designing it. For the test I used a Tiva Launchpad and a ADS1299 demo kit (only the upper board with the ADS1299 mounted). I used wires to connect the 2 boards with all signals needed (included also +5v,+3.3v and GND from Tiva board). I developed the firmware and the Matlab GUI and everything worked great. After that I proceeded with the design and realization of my own board for the ADS1299. Trying it, I am having a problem in the power management ICs, especially with the TPS60403 device. It is supposed to have -5v in its output but it is not working well, I get just -1.6v. I choose the same ICs recommended by the ADS1299 demo kit user guide (TPS60403, TPS72325, TPS73225). It seems that now the current required after the Voltage Inverter is higher than the 60mA available from the TPS60403, but why? In the trial system was working but not now, do you have any idea or suggestions for me?
    Thanks

  • 0 in reply to EnzoM
    TI__Guru*** 142860 points
    The first step would be to compare the waveforms on your working board to your new board. Look at Vin and Vout of the TPS6040x and see how they are different. You can post them here and I'll comment.
  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Hello again Chris,

    I took few shots from my board and from the previous test system.

    So, starting from my board:
    this is the input of the voltage inverter TPS60403, directly taken from the Tiva Launchpad USB +5v

    ..and this is what I am getting in its output

    ..and what there is on the Cfly capacitor

    And now, these are taken from the test system (Tiva Launchpad + ADS1299 demo kit):
    The input is, as before, the Vbus of the Tiva Launchpad.
    TPS60403 output:

    ..and Cfly capacitor

    As I said, it seems that the current absorption after the voltage inverter is now higher than the maximum current deliverable from the TPS60403.
    This is really strange because the -5V goes only to the negative voltage regulator TPS72325. I tried to remove it and the voltage inverter worked well, so I replaced the negative regulator with a new one but, unfortunately, nothing changed.

    Do you have any idea on what is happening?

    Thanks

  • 0 in reply to EnzoM
    TI__Guru*** 142860 points
    You need to measure the 5V input at the TPS6040x's Vin pin to see the effect of IR drop on your board.

    You could add a 1 Ohm resistor between the TPS6040x output and the LDO input to measure the current flowing. If there is more current on your new board, then you need to debug the LDO's loads and see why they are drawing more current now.
  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Hi Chris,

    at first, thanks for your support!
    I fixed that problem!
    I found out that RESV1 pin was erroneously contacting with neighboring AVSS pin, causing the strange (but understandable) current consumption as well as overheating the IC.
    Now everything works fine! :)

    Have a nice new year!
    BR
    Enzo