XTR111: Mosfet & Transistor selection

PossitiveByte

Part Number: XTR111

Hi everyone.

On the circuit diagram provided on the datasheet, there is a MOSFET and a transistor that need to be implemented separately by the end user. I've been doing some research and modeled the circuit on Tina, but I don't really know what specific components I should buy (referring to the MOSFET and transistor). Could someone please provide some advise on what I specifically need to look for?

Kind regards,

Dani

over 7 years ago

0 kai klaas69 over 7 years ago

Guru 140200 points

Hi Dani,

the datasheet contains very detailed information about this MOSFET. Have you read the section "External Mosfet"? Have you seen "Table 1" ?

Kai

0 kai klaas69 over 7 years ago in reply to kai klaas69

Guru 140200 points

Hi Dani,

could you find a proper MOSFET?

Kai

0 Luis Chioye over 7 years ago in reply to kai klaas69

TI__Guru 55466 points

Hi Dani,

As Kai suggested, Table 1 from the datasheet has some suggestions for Pchannel MOSFETs.

Please feel free to post if you have additional questions.

Thank you,

Best Regards,

Luis

0 PossitiveByte over 7 years ago in reply to Luis Chioye

Prodigy 60 points

Thank you very much Luis,

I ended up using Infineon's BSP170P at it is working flawlessly. There is just one last question I have regarding this. What sets the maximum current allowed by the current limiting circuit? My current set up looks exactly like the one on the specifications sheet, with the 15 ohm resistors.

0 kai klaas69 over 7 years ago in reply to PossitiveByte

Guru 140200 points

Hi Dani,

37mA flowing through the 15R resistor causes a voltage drop of 0.555V. This makes Q2 turning-on and limiting the gate source voltage of Q1.

Kai

0 PossitiveByte over 7 years ago in reply to kai klaas69

Prodigy 60 points

Hi Kai,

So whenever there is a voltage drop of 0.555V, the gate closes?

Do you have any other examples where I can understand better the logic behind the circuit?

If I substituted the 15 ohm resistor with a 35 ohm one, would that shut down the gate if the current surpasses 16 mA?

Regards,

Dani

0 kai klaas69 over 7 years ago in reply to PossitiveByte

Guru 140200 points

Hi Dani,

it does not close the gate. It limits the gate source voltage. Or by other words, it prevents that the gate source voltage furtherly increases.

When you increase the 15R resistor, then the current limit decreases. How much exactly depends on the transistor and on temperature.

But this current limiting is only inetnded for preventing damage and not for normal operation.

Kai

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XTR111: Mosfet & Transistor selection