Boost Converter IC with Current limiting feature

Hi Ali,

TPS61390/1 can support so high output voltage. But it is mainly used for APD bias, so it is a little complex and a external diode is needed. If you can use external mosfet, there are many boost controller you can choose such as LM5155.

Hi,
What is an APD Bias? I don't want to use many components due to the small size of the product. If I use TPS61390 then what complexities, I can face?
What will be the purpose of external MOSFET in the case of LM5155?

Hi Ali,

If you load current is no more than 30mA, tps61390 could be used. The complexities actually means it has pins you do not need.

For LM5155, it is a Boost controller, two Mosfets of boost are outside of the device. So it is easy to achieve higher voltage and power rating.

Hi
I tried to create a schematic at WEBENCH using the following inputs for LM5155

Vin = 3 to 4.2V
Vout = 50V
Iout = 10mA

It gives me errors. I also tried to figure out TPS61390 but as you mentioned above that it is complex due to APD so I skipped it. Also, it requires many components. 
I am designing a TENS machine and I just have to generate a PWM signal of higher voltage with the lower current because PAD resistance will be 500ohm. 
I have to boost the single-cell lipo battery voltages to some higher voltages and then generate square waves using transistors by applying PWM signal at the gate of MOSFETS.

Hi Ali,

For LM5155, the default input range is 3.5V to 45V but it can be configured to 2.97V minimum, that's why you meet errors. 

As I tried, TPS61391 should be a good reference and it is less complex. 

https://webench.ti.com/power-designer/switching-regulator/customize/7?noparams=0

Hi,
Thanks for the reply.
Whenever, I open WEBENCH, This message pop up. Is it something that I should worry about efficiency?
The TPS61391 efficiency validation is prone to ~ 5% ~ 10% mismatch from the bench data The switching frequency of TPS61391 is modelled at fixed 700kHz. However, it may vary over a higher load

Hi Ali,

It is normal. The Webench model is not perfect. 

Hi,
Thanks for clearing all my above points.
I have one last concern then I think everything will be good.
The TPS61391 will not provide the current more than the setup value irrespective of the source current or load demand?
As I mentioned above, that I am designing a TENS machine in which two pads will connect with the body and apply voltages pulses. I am boosting lipo battery voltages to 50V then converting that boosted voltage to a square wave using a microcontroller and MOSFET. Then I will apply these pulses to a TENS Pad which will attach to the body. The current through pads should not pass more than 30mA and for that, I need the current limiting feature in the boost IC. I hope you got my point. Thanks

Hi Ali,

I got it. So you want less than 30mA output current, right? If so, tps61391 can be used in another way. You should use APD pin as output pin like Figure10 in datasheet. The output current of APD pin can be limited by Rshort. These links can be good references.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/897356/tps61390-question-related-to-current-mirror-monitoring/3318032

https://www.ti.com/lit/an/slvaeh5/slvaeh5.pdf

Hi,
Is it possible if you can provide me a schematic for it?
If you can provide me WEBENCH design that would be great. 
thanks