NHS3152 AN0_5 is sitting at ~2.0V without Firmware, yet the data sheet states it is a max 3.6V tolerant Input. In the schematic VBAT is 3V the voltage divider is used to measure the Vbat at its actual voltage within the 1.744V limit to the ADC.
What do you mean "without firmware"? Did you erase all firmware sectors? In any case, the bootloader must have run.
Assuming you are using the latest SDK - after calling Board_Init() PIO2 will have an internal pulldown (~72kOhm), and the analog pads have an internal pulldown (~47kOhm).
With these typical values there will be ~2.25V at AN0_5 in your schematic. The pad is not clamped to 2V but to VBAT.
Note: in this configuration, current will be continually injected in the IO ring while in Power-off mode. This mode is not supported. If your use case uses the power-off mode, the PIOs should not be tied directly or indirectly to VBAT.
Hope this helps,BR,Dries.
Yes I erased all sectors using the latest LPCExpress tool. It looks like I can not use this circuit to measure VBAT because I will use the power down modes . Does the NHS3152 have a way to measure the VDDBAT voltage without external connections?
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If I understand correctly does the limitation of no injected current into the PIO ring during the power Off mode apply to the Reset Pin?
Connecting RESETN to the same supply as provided to VDDBAT is OK for as long as the battery is present. You will get problems powering via NFC if the battery dies afterwards, however. Best is to not connect RESETN if you do not intend to use it.
I have a 0.1uF connected to the RESETN pin on my PCA which is causing the NHS3152 to come up in the active state instead of the power down mode from a Power Off condition. Do you recommend I remove the cap?
I added below yellow state to the power diagram in your “NHS31xx Power modes” power point. You should add the yellow diagram it will really help me understand this PMU unit. I confirmed this behavior with the therapy adherence PCA running the Resistive 13 code.
If you want, you can change the 100 nF for a 1 nF cap (see also in the datasheet, chapter Static characteristics, "external capacitance on pin RESETN"). This will still provide some ESD protection and will delay startup minimally.
Tx for the suggestion to the power point! Much appreciated, that extra state will be added in the training slide deck.
Does the NHS3152 have a way to measure the VDDBAT voltage without external connections?
I am in the same situation and question as Kelvin. Anyone has a solution?
No, the NHS3152 IC cannot do that.
In SDK 12.3, a battery impedance check is added. This allows to query the IC via NFC to check whether the battery can supply sufficient voltage during a more severe load.
This is not the same thing: the IC cannot tell you the battery voltage. Instead, it can tell you under which load the battery voltage will drop below 1.85V.
Check for the module batimp in the latest SDK, and do read its documentation: <SDK>/docs/firmware.html > Documentation of the high-level abstraction modules > batimp: Battery impedance check module
The check uses the current drive mode of the otherwise unused high-source pads to increase the load on the battery. This allows you to detect a low or high battery impedance, which in turn is a good indicator of the expected remaining lifetime of the battery.
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