TPS65217C Brownout issue @ Powerfail

Sebastian,
See if this post helps: e2e.ti.com/.../1465529
Janice

Hi Janic,

thanks for your answer, the post  e2e.ti.com/.../1465529 are very useful!

I must be adapt the Pulldown Resistor (@Vsys)  on my curicit design, and bang went the Brownout Issue!

Put i have a further question, in chapter 9.3.9.1 in the TPS65217 datesheet, I can read that the Vac must be drop below the fixed threshold = 4,1V @ >= 50ms.
I believed that the Vsys must drop to the Vuvlo+Voffset and in the scope screen ... above in the post you can see that the Vsys is droped to <=2,5V

In your post you wrote: Try putting a pull down resistor, about 100K, on the system pin and see if that helps. This will drain the charge from the system pin so when AC is reapplied it will trip the power path circuitry. 

I can not found a Vsys threshold and a certain time for a safe powerfail cycle - How can i found the Vsys specification?

As you can see the Vsys goes not to GND ... this raises the question of whether i'm keeping the specification?

Thanks & Regards
Sebastian

Hi Janice,

the Brownout issue is still present :(

Thanks & Regards
Sebastian

Hi Sebastian

i've the same problem even using a battery backup, when the battery is under Vuvlo and i have a short deep on VAC=4,6V during the connection the system is frozen without Vldo1 and charging. In this state no reset and no PBint are usable a big problem. The only solution is disconnect the ac for one second or more in my case.

Favaro,

If you change the UVLO to the lowest setting, 2.73V, do you still see this problem?

Janice

HI

normally we set the Vuvlo at 2,89V  not the lowest limit  so we extend the period where my product is into OFF state, 80uA from battery and we are sensitive to first AC front; if the battery is over this limit the system start fine and recharge the battery . If under this limit the system take the first AC but if i have a disconnected situation and reconnect AC power into 800mS or 1 second the system is frozen without charging the battery and power path connected on internal battery low.

We have updated the first installation procedure where this situation can happen during the  connection with poor contact, normally the battery is a backup battery so this situation is rare.

What does it mean  Tdg(DT) power detect deglitch? 22,5mS?  mybe it mean that a AC disconnection shortest of 22,5mS is filtered? 

Favaro,

The AC line is connected to the SYS pin via a switch and has a delay detect time of 22.5mS, meaning once the circuitry detects voltage on the AC pin it takes about 22.5mS to close the path between the AC pin and the SYS pin. This is not the case for the BAT pin because it is hardwired to the SYS pin.

Janice