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LED Drivers/LCD Bias
LED Drivers/LCD Bias Forum
TPS65131 draws to high current when no load connected
i'm using the TPS65131 for multiple of my designs adn now we are validating the first design and notce that the TPS65131 draws to much current even when no load is conneted. below is the schematic
i have removed teh firete beads to make sure that no load is connected. now when i apply 5V and enable the smps it starts drawing 350 - 425 mA???
I have checked that the diodes are mounted ok and they are. the +15V and -15V are generated.
when i remove the DIODE in the positive boost circuitry it also generates +15V but than without drawing the high current.
our board space is limited but we managed to stick to the ref design as much as possible but 100%.
What can cause the tps to draw such high current??
when i have the tps running and than i can connect the load and it keeps running but after power down and power up it will no start again whit load connected. i need to first disconnect??
kind regards Martijn Broens
some additional info after testing.
when i power up my board and enable the TPS (no load connected and no Diode inserted (Positive boost section) than i can start up the tps no problem.
now after that it has started and i have my 15Vpos i can than place the diode on the PCB and the system remains working without drawing additional current. and i can even connect my load to it no change. but i can still not power up with either load or diode in place.
to me this seemd a startup issue for the tps?? pls advice
Please excuse the delay in response.
To be honest, I never saw such a high input current. Would it be possible to get voltage waveforms of the input and output voltage and the boost switch pin? (It seems that the boost is the issue because you say that the current is gone when the boost diode is removed.) Could you check as well the inductor current and send a waveform?
Just to make sure that we are talking about the same thing:
- You remove CR1107 and then the high input current is gone?
no problem i'm already glad that you respond.
no problem i can make the shots tomorrow and send them to you or should i post them here?
indead it is the boost side that shows this effect. i also have some inrush current picturers aswell. how would you suggest to measure the inductor current?
yes i did mean CR1107. it so seams that the switcher than uses its internal fet forward diode for boosting, meaning it wil create the voltage but it will not be able to provide current.
I already have an eval board and i already connected it to my own board but that the eval does nt draw this high inrush current. (@ the eval i hardwired PSP, PSN, ESP, ESN together and connected them to my sys_on (R2561))
In the mean time we already verified 4 other boards and all with the same effect/result. unfortunatly i can not (for now) sen you a board as we can not miss it at the moment, we need them to verify the remainder of the board just by applying external +/-15V
For the measurements, please take the way you prefer. you can post them here or send them privately.
I heard that you are already exchanging parts from the EVM to your board to check if this changes anything. To be honest, I would go the other way: keep the EVM connected instead of your outputs and exchange the parts that you are using to the EVM. If then the EVM still works fine with your load, at least the parts that you are using externally are not causing an issue. Then I suggest to rework the layout to keep it as close as possible to the EVM layout. I can review your new layout before you go to production.
Some additional ideas:
- please check if exchanging C2554 (next to the top resistor of the resistive divider) with 12pF helps.- please measure the input voltage. I wonder if the input capacitance is not big enough for the line impedance of the 5V line. Please check if an additional low impedance input cap close to the inductor helps the issue.
Good morning Brigitte,
thank you again for posting,
i have no probmlem uploading to the forum but there are some items than i'm not allowed to share on a forum. can you pls send me a direct email so i can repley to that.
please find below the snap shot from my scope
What you see is the following:
CH1 (Yellow): VDD_15V Output from switcher TN2307)
CH2(Bleu): NP (measured between Boost inductor and Forward diode (L1903l CR1107)
CH3 (Violet) I5v: current consumption of switcher.
CH4 (Green) VDD_5Vin 5V supply
The test setup is as follows:
External powersupply set to 5V no current limit (max 10Amp).
removed R2561 from design and added a switch between VDD_5V_MAIN and ENP node
powerup the board wait for the board to become running. this is why you already see current consumption of approx 250mA. than when i enable the switch the smps draws 2.69Amp inrush, way to high i would saythan after approx 121us the inrush peak is gone and current consuption falls to 230mA total.
414us later the switcher kicks in and as such current again inreases to 1.73Amp and VDD_15V grows.
than the first periode that the switcher does not seem to do anything current is falls from 1,73A to 710mA (Screenshot 3)
than aftre the second periode current again drops to 210mA and Vout remains.
be aware that all this is under NO_LOAD condition (E704 and E703 removed
To me it still seems that the inrush is whats killing me as in our app we can not handle this large inrush. it will reset our SOC
hope this helps
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