TPS2064C / Discharge function

Kuramochi Tadahiko

Other Parts Discussed in Thread: TPS2064C

Hi,

Which case do you suppose when discharge function is triggered by UVLO?

The datasheet p18 is mentioned that ". A 470 Ω (typical) discharge resistor will dissipate stored charge and leakage current on OUTx when the device is in UVLO or disabled. "

I think complete discharge is not able because it takes over 300msec until electrical charge is discharge whenthe output capacitor 150uF such as following file.

TPS2064C discharge sim.xlsx

Best Regards,

Kuramochi

over 7 years ago

0 Aleksandras_Kaknevicius over 7 years ago

TI__Genius 15710 points

Hi Kuramochi,

This part falls under the power interface forum. I will go ahead and move this post.

Thanks,

Alek Kaknevicius

0 JCHK over 7 years ago

TI__Mastermind 43610 points

Hi Kuromachi-san,

Have you checked the discharge function by cycling the enable? The TPS2064C datasheet only mentions UVLO rising, it does not mention the falling case. If this threshold is too low, the device may not have enough headroom to turn on the discharge FET which may be what we are seeing.

Can you confirm that the discharge function works when the device is disabled?

0 Kuramochi Tadahiko over 7 years ago in reply to JCHK

Guru 28715 points

Hi John-san,

Thank you for your help.

I apologize that my explanation was poor.
P-GOOD is connected to EN, so the device is disable when P-GOOD is low.

Best Regards,
Kuramochi

0 Kuramochi Tadahiko over 7 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

Hi John-san,

How is this situation?
Please let me know if I misunderstand.l

Best Regards,
Kuramochi

0 JCHK over 7 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 43610 points

Hi Kuramochi-san,

So is EN pin failing at the same time as the input voltage is falling? The reason I am asking is There is a delay from EN going low to the device responding:

So if the input voltage falls at the same time as EN, we may not have the ability to discharge the output.

Can you capture VIN, VOUT, and EN with an oscilloscope so we can see the timing?

Thank you,

0 Kuramochi Tadahiko over 7 years ago in reply to JCHK

Guru 28715 points

John-san,

Thank you for your kindness.

I understood.

I edited the previous file, can you find it?

TPS2064C discharge sim (2).xlsx

And the discharge register of this device is 600Ω.

I think this resistance is too large to discharge 100uF order capacitor.

What do you think?

Best Regards,

Kuramochi

0 Kuramochi Tadahiko over 7 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

John-san,
How is this situation?

Best Regards,
Kuramochi

0 Kuramochi Tadahiko over 7 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

John-san,

Could you tell me why the discharge resistor is 600Ω?
I must explain this reason to my customer.

Best Regards,
Kuramochi

0 Eric Wright over 7 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 42795 points

Kuramochi-san,

The reason is mostly IC design based (limit internal power dissipation, discharge current, etc.) and is a reasonable value to allow a reasonably swift discharge of VBUS capacitance. For USB type C devices, there are USB Type C spec based requirements too that will factor in.

0 Kuramochi Tadahiko over 7 years ago in reply to Eric Wright

Guru 28715 points

Eric-san,

Thank you for your information.

However, this device can not discharge VBUS capacitaoance quickly as the attached file of my initial post.

Best Regards,
Kuramochi

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TPS2064C / Discharge function