LM2776: Advice for protecting charge pump inverter when used as external voltage

David Dean

Part Number: LM2776
Other Parts Discussed in Thread: TLV61046A, TPS61046, LMR36006, LMR36006-Q1, TPS2595, LMR36015

My current system has 5V available and I need to provide 10V to an external device. It is OK if this external voltage is not referenced to GND, and given some size and cost constraints, I think the smallest solution it to use an inverter (like the LM2776) and provide +5 and -5 to the external device, who should be happy to see 10V (let me know if this is incorrect).

Assuming that this is a valid way to provide a 10V output, my concern is how to protect the LM2776 from ESD, or any other normal concerns related to an external connection. For example on the +5V side I can use a diode to prevent reverse voltage, but on the -5V side that diode would need the opposite polarity, which would not help if a positive voltage is accidentally applied to that pin.

Perhaps there is an application note available that would help with this?

over 5 years ago

0 Chris Glaser over 5 years ago

TI__Guru*** 142750 points

Hi David,

TI makes ESD protection devices, which you can find here: www.ti.com/.../overview.html

How much current will the 10V load draw?

0 David Dean over 5 years ago in reply to Chris Glaser

Expert 2305 points

About 100mA.

ESD isn't my biggest concern, I know I can just put some TVS diodes (or similar) from both outputs to GND. Reverse voltage might be the larger concern - the product has an input and output connection and it's possible (but hopefully unlikely) that the user will accidentally connect the input to the output. If the output were simply 10V and GND, I'd put a diode on the 10V signal and be done. But I don't see how I can do that with the -5V signal.

0 Chris Glaser over 5 years ago in reply to David Dean

TI__Guru*** 142750 points

Thanks for explaining.

At 100 mA, the output will be around -4.7V due to the output impedance, so you won't quite achieve 10V. Is this ok for your application?

I think most designers would use a mechanical method (for example, a keyed plug/connector) to ensure that the wires don't get swapped by mistake.

0 Jasper Li over 5 years ago

TI__Mastermind 46905 points

Hi David,
do you also consider a boost converter, such as TLV61046A, or TPS61046 if BGA package is also acceptable.
compared with charge pump, a 0805 package inductor is required to achieve the boost function. but you can get a regulated 10V when the input voltage changes.

0 David Dean over 5 years ago in reply to Jasper Li

Expert 2305 points

I have but the charge pump solution seemed simpler and smaller - at least at first, as the TLV61046A looks very interesting. Boost regulators did have the issue where I could not turn off the output without additional circuitry but it looks like the TLV61046A solves this with the isolation switch, so this might work. Just to be clear, this means that when I disable the converter, Vout will fall to 0V, correct?

0 Jasper Li over 5 years ago in reply to David Dean

TI__Mastermind 46905 points

Hi David,

yes. Vout will be zero if the disable the converter. this device can also protect output short circuit.

0 Chris Glaser over 5 years ago in reply to Jasper Li

TI__Guru*** 142750 points

Hi David,

The first half of this circuit is a very small 36Vin buck: www.ti.com/.../PMP15039

0 David Dean over 5 years ago in reply to Chris Glaser

Expert 2305 points

This is the LMR36006? That is very interesting! Is this a brand-new part? I admit to doing most of my component searching though Digikey and it looks like it's not available there yet. Is this part in production with normal availability?

0 Arief Hernadi over 5 years ago in reply to David Dean

TI__Mastermind 23815 points

Hi David

The LMR36006-Q1 is actually released

http://www.ti.com/product/LMR36006-q1

Thanks

-Arief

0 David Dean over 5 years ago in reply to Jasper Li

Expert 2305 points

Hi Jasper,

One followup on the TLV61046A. In some applications I may want to turn the output on and off at around 5 - 10 Hz. I previously would have done this with a separate switch, but I'd prefer to take advantage of the EN pin and the load disconnect feature. In other applications the input voltage may turn on and off at frequencies as high as 30 Hz. I don't really have any control over this and the regulator would be enabled and disabled as VIN goes above and below the UVLO threshold.

Could either of these harm the TLV61046A?

0 Jasper Li over 5 years ago in reply to David Dean

TI__Mastermind 46905 points

Hi David,
it is OK. I don't see risk to harm the TLV61046A in the two case.

0 David Dean over 5 years ago in reply to Jasper Li

Expert 2305 points

Great, thanks.

Another minor concern. The max voltage for the TLV61046A is 5.5V. My product has a USB charger output and I plan to power the TLV61046A from the 5V output. While this will be well regulated to 5V (or maybe 5.25V), my concern is what could happen since the signal goes to the outside world. I have ESD protection but would be concerned about what a poorly-designed USB device could do, or a high voltage ripple from a long cable plugging in, things like that. Do you have any real-world concerns about using the TLV61046A in that setting?

0 Jasper Li over 5 years ago in reply to David Dean

TI__Mastermind 46905 points

Hi David,
the input of the TLV61046A much be limited below 5.5V.
as I know, you may need to a load switch between the USB and the input of the boost converter. however, I know little about load switch device. I need time to find some material to reply your question.

0 David Dean over 5 years ago in reply to Jasper Li

Expert 2305 points

Thanks Jasper, I look forward to hearing back from you once a reply is ready. Thanks!

0 Jasper Li over 5 years ago in reply to David Dean

TI__Mastermind 46905 points

Hi David,
if the input voltage of the USB could be higher than 6V in your system, I would suggest you add an E-fuse such as TPS2595 to limit the input voltage not higher than 6V. 6V is maximum input voltage of the TLV61046A.
I don't know much about the e-fush device, so I suggest you create a new post about the e-fuse device.

if just want to limit the high ripple during plug in, you can try to add a resistor in series with the capacitor to avoid ringing after plug in

0 David Dean over 5 years ago in reply to Jasper Li

Expert 2305 points

I don't think I'm concerned that Vusb could be higher than 6V, so the E-fuse shouldn't be necessary. It's mostly a concern about ripple or ringing. Could you send me a sketch of the proposed circuit with the resistor?

0 Jasper Li over 5 years ago in reply to David Dean

TI__Mastermind 46905 points

Hi David,
it depends on the inductance of the cable. it is RLC circuit, we need a R that can over damp the circuit.
another solution can be refer to the page 18 "USB Soft Connect Circuit" in "www.analog.com/.../3559fb.pdf"

0 David Dean over 5 years ago in reply to Jasper Li

Expert 2305 points

Hi Jasper,

Sorry if I wasn't clear, but my product is the USB host, and generates the 5V, so I don't think the slow connect feature would work in this case.

The scenario in that note seems to refer to a voltage spike on the USB device side. Is there another situation that will cause a spike like that on the host side? Or will that 10V spike bounce back to the host side as well?

0 Jasper Li over 5 years ago in reply to David Dean

TI__Mastermind 46905 points

Hi David,
the 10V voltage spike is caused by the inductor of the cable and the capacitor in USB device. it can't bounce back to the host side.

0 David Dean over 5 years ago in reply to Arief Hernadi

Expert 2305 points

Do you know anything about future availability of this part? I finally got a chance to test the LMR36006 and it looks just about ideal. However, while there are some available in the TI store, it is not in stock with any distributors, nor is the LMR36015. Do you know if these will soon be more widely in stock?

0 Katelyn Wiggenhorn over 5 years ago in reply to David Dean

TI__Genius 11040 points

Hello,

You can place an order through distribution and then, they will provide a lead time. This device is available in small quantities (approximately 10) through distribution (Digikey/Mouser). Once you place an order, it should be processed in a week.

Please let me know if you have any additional questions.

Best Regards,
Katelyn

Power management

Power management forum

LM2776: Advice for protecting charge pump inverter when used as external voltage