VSTORE and LDO2 Voltage Drop When Loading STEVAL-ISV019V1

[HUANG2]

[Moderation] Separated from the previous thread, as the STEVAL-ISV019V1 is a different topic.

Hi,
As the questioner mentioned, the voltage measured on the STORE pin is about 2.416V. Should we charge the battery at this time? What conditions can raise the voltage of STORE to VEOC.

Thank you for your reply and your help.

[Peter BENSCH]

Welcome @HUANG2, to the community!

Important is:

• the pass transistor remains open as long as VSTOREV does not reach the EOC threshold
• according to your schematic, VEOC with the resistors is about 4.21V
• only above VEOC is the internal path enabled, so that LDO2 can become active and the supply can be switched through accordingly

VSTORE only rises sufficiently if more energy is supplied to the storage capacitor or the STORE node than is drawn from it, for example by:

• The energy source at IN_LV must deliver enough power. If the source is too weak, VSTORE remains below the switching threshold.
• Enough charging time for the STORE capacitor to charge. Small currents or a high load prevent VEOC from being reached.
• If the load on LDO2 or the system is too high, the voltage on STORE is pulled down again.
• Missing or incorrect connection of BATT, STORE, LDO2_EN, external resistor dividers or protection paths can prevent charging. Also important: no unwanted leakage current or short circuit at the STORE node.

Check:

• measure VSTORE directly while the source at IN_LV is active
• vheck whether the STORE capacitor is correctly dimensioned
• reduce the load on LDO2 as a test
• check whether the circuit can really rise to VEOC ~4.21V

As long as VSTORE does not reach VEOC, LDO2 remains off. The battery is not meaningfully enabled in this state. Only when STORE rises above the EOC threshold through sufficient energy input does the internal pass transistor close.

Regards
/Peter

[HUANG2]

The ST Community moderator has translated the post to comply with the language of the Community which is English.  For more information, see: ST Community Terms and Conditions - STMicroelectronics Community

Hello,

I purchased the STEVAL-ISV019V1 evaluation board. After connecting the solar panel, the VSTORE voltage reached the EOC threshold, and the LDO2 output voltage was also normal and stable at 3.3V. However, when I used LDO2 to power the sensor node, the VSTORE voltage dropped and the LDO2 output voltage fell to 1.2V. After that, I disconnected the load and measured the VSTORE voltage at 2.881V. However, the VSTORE voltage did not rise again for a long time. What could be causing this? Is it possible that the chip is damaged, or that another component has failed?

My solar panel open-circuit voltage is between 2.8V and 3.4V.

Thank you for your reply and help.