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USB EZ-PD™ Type-C Forum Discussions

NaMe_2085021
Level 4
Level 4
25 replies posted 10 replies posted 10 questions asked
Are the transistors correctly connected?
Are the transistors correctly connected?

      

2mosfet.png

Аre the transistors correctly connected?

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1 Solution
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DaBl_4548126
Level 2
Level 2
First solution authored First like received Welcome!

Because there is a parasitic body diode inside the FET, so you need to place two "back-to-back" (i.e. source to source as shown) to prevent discharging  the battery (via the FET body diode) when the charger is unpowered. This way, if the FETs are off, no current can flow in either direction.

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If I do not use the battery?

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Well, I guess it depends on what (if anything) you have connected to the "Consumer Path". If nothing is connected there, you could delete those FETs entirely, as in Figure 11. But if you have circuitry there, I think you may need to be able to disconnect it as part of the power negotiation process, even if you don't have a battery. (I'm not familiar with this particular chip, but I have some knowledge of laptop charging circuits in general.)

I thought your question was a general "why do I need two FETs when one should do?", and the answer is that when it is possible for current to flow "from the load" via the body diode, as when you are charging a battery.

Perhaps you need to contact Cypress technical support. I'm just a fellow user.

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Thank you very much!

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NaMe_2085021
Level 4
Level 4
25 replies posted 10 replies posted 10 questions asked

I don't understand how it  works. Please, help me.

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Thank you!

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