TPS61202: Blows the inductor (latched internal driver?) under load

Guy Marsden

Part Number: TPS61202
Other Parts Discussed in Thread: TPS61200, TPS61252

I'm using the chip in a power bank design with a single Li-pol battery to drive 5V out for phone charging. It works fine with 20mA LED load (around 5.6V) but smokes the chip and inductor when a phone is connected (high load). I'm not an experienced power designer. Did I do something dumb?

over 5 years ago

0 Jasper Li over 5 years ago

TI__Mastermind 46905 points

Hi Guy,

Please share the BOM and layout. I will check if there’s any risk.

0 Guy Marsden over 5 years ago in reply to Jasper Li

Prodigy 80 points

Thanks for taking a look Jasper. Here's the BOM + layout. I know the layout could be improved - it's a first proto. I'm baffled why a heavy load causes the chip to lock up and smoke the inductor. I'm testing on a bench supply because the safety PCB in my 200mAh Li-pol battery would shut down when the circuit shorted out. It's really tedious to replace the chip - I use a heat gun and low melting point solder paste (Chipquik SMDLTLFP).

0 Guy Marsden over 5 years ago in reply to Guy Marsden

Prodigy 80 points

I'm hoping someone (Jasper) can respond to this question. Trying to get this prototype working and tested for pre-production!

Guy

0 Jasper Li over 5 years ago in reply to Guy Marsden

TI__Mastermind 46905 points

Hi Guy,

sorry for the late as busy these day.

I think the root cause is the layout. the high voltage spike in the SW pin kill the IC. please refer to this application note to modify the layout www.ti.com/.../slva773.pdf: changing the location of the output capacitor in current board or build new board.

no sure about the output current? from the input and output voltage the TPS61200 is not the suitable solution. a device as TPS61252 should be better.

0 Guy Marsden over 5 years ago in reply to Jasper Li

Prodigy 80 points

What SW pin? And the App note link you gave is bad. You're not being helpful here.

0 Jasper Li over 5 years ago in reply to Guy Marsden

TI__Mastermind 46905 points

Hi Guy,

this is the link www.ti.com/.../slva773.pdf
The SW pin is the L pin in this device, as this pin is always switching.

0 Guy Marsden over 5 years ago in reply to Jasper Li

Prodigy 80 points

Thanks,
The design note is helpful. I keep thinking like an analog circuit designer and forgetting the high frequency issues in these topologies.

0 Guy Marsden over 5 years ago in reply to Guy Marsden

Prodigy 80 points

I like the TPS61252 - cleaner and simpler. Here's my updated design. The PCB has a full ground plane under the whole area.

0 Jasper Li over 5 years ago in reply to Guy Marsden

TI__Mastermind 46905 points

Hi Yoda,

In the schematic, please place a ceramic output capacitor closed to the IC. or change C8 to ceramic capacitor.
the PCB is good.

0 Guy Marsden over 5 years ago in reply to Jasper Li

Prodigy 80 points

I built the circuit and used a ceramic 47uF cap at C8 per your suggestion. It worked fine driving an adjustable load (USB tester) and I ran it up to 1A input (about .82A output when it started to limit. Using iLim at 10K. SO far, so good. Then I connected the output to a small bluetooth speaker via uUSB to charge it. Input current went to .8A for a few seconds, then the chip blew and shorted the (current limited) power supply I was using to simulate the li-pol battery (set to 3.8V). SO I'm back to square one. This is getting annoying and expensive and my client is getting impatient.

I don't appreciate your taking WEEKS to respond.

Guy

0 Jasper Li over 5 years ago in reply to Guy Marsden

TI__Mastermind 46905 points

Hi Guy,

sorry for the late reply as busy last week.

do you mean the IC is still damaged after you change to TPS61252?
may i know the inductor part number? i need to check if the inductor become saturation.
could you measure the VIN, VOUT and SW waveform when power the blue speaker.

0 Guy Marsden over 5 years ago in reply to Jasper Li

Prodigy 80 points

Yes TPS61252DSGR has blown under load

Inductor is a Wurth 1.5uH 1.7A 47mOhm part# 744031001 as recommended in the spec sheet

I cant take power measurements because the chip blows when trying to charge the bluetooth speaker (or any uUSB battery load).

It's weird that it works fine with a USB load simulator up to .8 Amp.

Guy

0 Jasper Li over 5 years ago in reply to Guy Marsden

TI__Mastermind 46905 points

Hi Guy,

the inductor should be OK.

what is output current when charge the bluetooth or battery load? I'm thinking if the overload causes the device shutdown, then high voltage at Vout pin as the ringing caused by long cable between the boost and the loading. as the failure of a converter is normally caused by over voltage at VIN, SW or VOUT pin.
that is why we need the waveform in these pin to observe what happen before the IC damage.

from the layout, I don't found the ground of the input, only the positive input to the inductor. is it in the bottom layer?

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

TI__Mastermind 46905 points

Hi Guy,

I haven’t heard back from you, I’m assuming you were able to resolve your issue. If not, just post a reply below

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TPS61202: Blows the inductor (latched internal driver?) under load