BQ25505 Questions on Supercap and Vbatt_OK

INg

Genius 3475 points

Could i check if there are any guidelines on the selection of Secondary storage elements(SSE)?

For example, there are several voltage rating for super cap.

If we would to select Vbatt_OV to 4.2, would a super cap with rated voltage of 4 , 4.2 or 4.5 work better.

DOes it make sense for to use a super cap rated at 6.3V but we will not be able to charge up (Vstor max is 5.5V)?

Which voltage rating is more sensible?

Like to zoom down on Typical application on 8.2.1

The design goals stated :

"VBAT_OK = 2.39 V, VBAT_OK_HYST = 2.80 V"

On figure 21, the Vbatt_ok starts following Vstor at around 3.2V. which is correct?

Ivan

over 8 years ago

0 Jing Zou over 8 years ago

TI__Mastermind 19480 points

You will need a super cap that is higher than your VBAT_OV setting. One of the reason is due to the dc saturation characteristic of the all capacitors, as the voltage reach on the cap reach its voltage rating, the capacitance of the cap can drop significantly.

The calculation is based on VBAT_OK = 2.39V and VBAT_OK_HYST = 2.8V. You can use the Design Help Tool in the link below for threshold setting.

http://www.ti.com/lit/zip/sluc484

0 INg over 8 years ago in reply to Jing Zou

Genius 3475 points

HI JIng Zou

Thanks for the advise on the supercap.

Can you also take a look at the second part of my post as well?

Ivan

0 Jing Zou over 8 years ago in reply to INg

TI__Mastermind 19480 points

I have already commented on my previous respond.
"The calculation in section 8.2.1.2 is based on VBAT_OK = 2.39V and VBAT_OK_HYST = 2.8V. You can use the Design Help Tool in the link below for threshold setting.
www.ti.com/.../sluc484 "

Power management

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BQ25505 Questions on Supercap and Vbatt_OK