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TPS62003 and TPS3511 with a lithium polymer battery

Hope Johnson
Prodigy 85 points
Other Parts Discussed in Thread: TPS2511, TPS63002

Hello TI community,

I'm designing a portable mobile phone/USB device charger using the TPS63002 chip to boost a 3.7V 2600mAh lithium ion battery (capable of producing up to 2A) to 5.0, then using the TPS2511 to put the device-specific voltages on the D+ and D- pins.  Using a power supply, I've successfully tested my design with a couple of devices, including an iphone5.  The iphone5 initially uses 1A or more of current from the power supply, then backs off to somewhere around 550-800mA. Note that this is read from the power supply.  

However, when I switched to the lithium ion battery, iPhone charging initially works fine, pulling roughly 250mA (as measured by my multimeter at the USB port), then slowly ramps down, until at some point it drops to around 180mA and the 'Accessory not supported' error shows up.

I thought that problem might be the voltage sag, so I've tried multiple values (from 50 - 200KOhm) for the Cs resistor (R2 in my schematic), but it hasn't made a difference.  I've also tried difference values (22uF - 2 x 47uF) for the Vin capacitor (C4 in my schematic).  I've also tried multiple types of lithium ion battery.  The one I'm currently using is rated at up to 4A, so I don't believe that's the problem.  Recently I've noted that the TPS63002 chip gives off some heat during the charging and has even started to make a low volume whirring noise.  Maybe the chip is damaged?

I'm including my schematic here.  I'd appreciate any pointers.

Thanks!2185.TPS2511wTPS63002.pdf

  • 0
    TI__Mastermind 42795 points

    Is the DC voltage sagging at the VCC node when the circuit mis-behaves? Maybe take a few DMM measurements of voltage during the event.

  • 0 in reply to Eric Wright
    Prodigy 85 points

    The VCC voltage sags a bit, but not below what's acceptable for USB charging.  With a 51KOhm Cs resistor (R2 in my schematic), I read 5.3V without load.  When the iphone is plugged in, it initially drops to ~5.03V, then stabilizes around 5.08V.  This all happens rapidly (within a second or so), and is concurrent with the error messages coming up on the screen.

    Any ideas?

  • 0 in reply to Hope Johnson
    TI__Mastermind 42795 points

    From what you've told me, the issue seems to lie with the TPS63002 and not the TPS2511. Can you provide an oscilloscope plot of the 5V bus when the "sagging" occurs? It may just be the transient response capability of the TPS63002. Once we get the plots, I can move this post over to the TPS63002 section of this forum so that those experts can help out.

  • 0 in reply to Eric Wright
    Prodigy 85 points

    I agree that my problem is probably an issue with the TPS63002 and not the TPS2511, but I was wondering if it might be an issue with the way I've connected them (i.e., the R2 resister).  I don't have immediate access to an oscilloscope, so it may take some time before I can show a plot of the sagging.  In the meanwhile, is there anything I could do to try to counteract the sagging?

  • 0 in reply to Hope Johnson
    TI__Mastermind 42795 points

    While I am not completely sure of any stability related issues that extra output capacitance might create, you can simply try a much larger output capacitor(s) feeding the 5V to the phone(s).

  • 0 in reply to Eric Wright
    Prodigy 85 points

    Thanks for the suggestion of using a larger output capacitor.  I tried up to 141uF, but the results were the same.

    Meanwhile, I found an oscilloscope and used it to read VCC while the iphone was connected and gave the error message.  The attached movie shows a typical example of what I saw (sorry that the movie is upside down).  Divisions on the scope are 2V and 50ms.  Initially, before plugging in the iPhone, VCC is steady at a bit over 5V (my multimeter read 5.3V).  At the moment the iPhone is plugged and instantly goes to the error message, VCC drops to just below 4V and in this case, remains there.  Sometimes the voltage popped back up to 5+V but didn't charge the phone. I'm guessing it stayed at 4V for this trial because I had the screen engaged.

    Could this somehow be remedied by changing the Cs resistor (R2) or it's configuration?  As I mentioned before, I have tried larger resistors here (up to the point where VCC = 6+V and is too high for USB charging) without any change in the result?

    Any ideas?

    Click here to play this video