TPS63900: Replacement part with input current limit

Hi  Jasper,

Since power supply for NB-IOT is 4V which is always higher than Vin, is a boost converter ok for you?

Regards

Tao

Hi  Jasper,

Glad to see TPS61094 match your application well.

If you have any further question about TPS61094, please let me know and i'll forward to my colleague who is taking care of this device.

Regards

Tao

Hi Tao, 

I have a 5F 3V supercapacitor.
I see that the capacitor charges very slowly.

1. ICHG_PRE is 250 mA when ICHG is equal or larger than 250 mA; ICHG_PRE is ICHG when ICHG is lower than 250 mA.
2. ICHG_TERM is 10 mA when ICHG is equal or larger than 10 mA;  ICHG_TERM is 2.5 mA when ICHG is lower than 10 mA.

I have set my charge to 75mA so I expected 75mA as pre limit but this is on the order of uA.
I do not see this in my measurements. Can you explain this further?

Vin    = 3.6V
Osel  = 3.3V
Vsup = 2.6V
Icur   = 75mA

Hello Jasper,

As I found the above picture in the TPS61094 datasheet, I expect that you are now using this part, right?

What is the voltage at your supercapacitor when you measure this low current? Can you share where you measure?

Best regards,
Brigitte

Hello brigitte,

I am indeed using the TPS61094. See the figure below for my measurement.
I expect the TPS61094 to charge the supercapacitor with a current of up to 75mA. So this doesn't happen.

Hello Jasper,

Which resistor do you have on VCHG pin? It looks as if the charging is terminated at 2.5V.

Best regards,
Brigitte

Hello brigitte,

The resistance is correct. The termination voltage is indeed 2.5V.
But the charging current is wrong, this is not the set Icharge (75mA).

I see that the TPS61094 also fails and the capacitor sometimes does not switch on? Is my current peak too high/too fast?
The voltage of the capacitor is still 1.5V. 

TPS61094 + 5F + LISOCL2 bobbin battery

These are my current peaks that I have to absorb with the TPS61094 and the supercapacitor.
Tested with a LISOCL2 spiral battery.



It should be possible to use an LTE modem with a LISOCL2 bobbin and a supercapacitor because there are plenty of products on the market.
Hopefully you can help me further.

Best regards,
Jasper

Hello Jasper,

If the termination voltage is 2.5V, the charging will stop when it reaches the 2.5V. So in your first picture it looks as if the charging is working until the voltage has reached 2.5V. Am I overlooking anything?

Best regards,
Brigitte

That is correct, but the current with which the capacitor charges is many times less than Ichg. This should just be 75mA, right?

Hello Jasper,

You mean that the current in your measurement steps up slowly instead of being from beginning 75mA, right?

Best regards,
Brigitte

Yess, And that sometimes the TPS61094 switches off because the pulse is too fast/too high

Hello Jasper,

The expert of this specific device is at the moment out of the office. Please expect an answer mid of the week.

Best regards,
Brigitte

Hi Jasper,

Can you share your schematic and layout? Also, do you have an oscilloscope. It'll be easier to find the root cause if you can provide waveform in 5us/div scale

Hi Brigitte,

Thank you for supporting this case. 

Best regards,

Travis

Hi Travis,

I am testing the TPS61094 for a new design with the evaluation kit.
An existing system with NB IOT is used as test system

A schematic representation of the system is as follows:

So a system with a LISOCL2 bobbin battery that has high current peaks with an NBIOT/LTE transmission
Is the TPS61094 the right choice or are there other choices that might be better?

Hi Jasper,

How much Amps can the high current peak be and how long does the current last?

Please share the EVM setup. How did you placed the jumper and how did you connect the inputs and outputs.

Also, please share waveform of VOUT , SW  , VSUP and VIN in 10us/div.

Best Regards,

Travis

Hi Travis,

The current peaks are shown in an earlier image in this forum. The peaks go to a maximum of 1A,

EVM Setup:
Csupercapacitor = 5F
Vout = 3.3V
Vcharge = 2.7V
Icharge = 75mA

EN = high
MODE = high

There is a ucurrent gold between Vin and the battery.
I hope to make a picture of VOUT, SW, VSUP and VIN today.

Hi Jasper,

Thank you for your information. Maximum current of 1A should be supported when VSUP>1.8V.

Please share picture of your test setup as well. Also, since the ucurrent gold between Vin and the battery, is the Ibat measured on VIN side or on VSUP side?

Best Regards,

Travis

Hi Travis,

Maximum current of 1A should be supported when VSUP>1.8V.
This means that the TPS61094 switches off if VSUP < 1.8V.
This could be the reason why the TPS61094 sometimes fails on a final RF transmission pulse.

Is the TPS61094 suitable for our application or do you think another component/idea is better?

Best regards,
Jasper

Hi Jasper,

When VSUP drops below 1.8V, the output power cannot be supported and the Vout drops below its target voltage. If you need to discharge super capacitor to below 1.8V, you'll need a discrete charger IC + boost IC solution. Please share your minimum VSUP and I'll recommend you another boost IC.

Best Regards,

Travis

Hi Travis,

Oh too bad. I thought it could be drained all the way down to 0.8V.
The TPS61094 was perfect because of the loose supercap voltage.

For a new design. I need current limit for the LISOCL2 + a supercap to process the RF pulses.
And the supercap should actually only have a maximum voltage of 3V because of the space claim -> 5F, 5V does not fit for example.

Hi Jasper,

I may not understand your application correctly. May I know where the super capacitor is placed? Is it on boost Vin or Vout?

Best Regards,

Travis

Hi Travis,

Right now I have such an application. I got this from TI's application note
Enable and mode are in automatic buck/boost and are not controlled by the MCU

www.ti.com/.../slvaf41a.pdf

Hi Jasper,

TPS61094 cannot support VSUP discharge down to 0.8V. For boost converters, the supported max Iout can be calculated by:

If you need 0.8V Vin, 3.3V Vout and 1A Iout, you'll need to select a boost with over 4.58A  current limit. So we recommend TPS61033 or TPS61022. I agree that TPS61094 is the perfect fit in power structure. It's a pity that we don't have a similar structure device supporting bigger current for now.

Best Regards,

Travis