ST25DV64KC Ultra Low Power Mode Not Working

[Alex_B]

Hello 

We're using the st25dv64kc 12pin package on a custom board and it is wired as shown below to our MCU which is the atxmega128a1.

Our product is battery powered so we keep the current draw from the battery minimal during long inactivity periods.
Normal current draw is 60uA but if the st25dvs interrupts are enabled the current draw goes up to 170uA even if the LPD is set to high and the VCC is set to low. If the st25dv starts up with interrupts disabled the draw remains 60uA but if the interrupts are enabled and afterwards disabled without power cycling the the device the draw does not goes down and stays at around 170uA.

The VDCG is connected directly to the main power source at 5V.


How can I get close to the stated under 1uA draw in ultra low power mode?

Thanks,
Alex

[JL. Lebon]

Hello, 

Some questions to try to understand what is going wrong here:

- how do you drive the LPD pin? which voltage do you apply at high level?

- what are the values of VCC_NFC and VCC (VCC=5V from what I understand)?

- where exactly are you measuring the currents? (VCC? VCC_NFC?)

- what do you mean by "interrupt are enabled": do you mean the register is set to enable output (GPO_EN bit) or do you mean interrupt is active (driving the signal from low to high)?

Best regards.

[Alex_B]

Hi,
- the LPD is driven via GPIO and high level is 3.2v

- VCC_NFC is driven via GPIO and is 3.2v and VCC is 3.7v not 5v as I wrote before.

- the current is measured in line with battery positive lead, the lead was cut and a multimeter is connected to ither side of the lead. the current measurement is of the whole board.

- yes "interrupt are enabled" refers to register is set output  via the GPO, more precisely GPO1 is set to 0x11.

Thanks,
Alex

[JL. Lebon]

Hello, 

When LPD is active, the power consumption is decrease on the VCC pin. So, it would be interesting to make the current measurement on the VCC_NFC power supply only to check the effect of LPD first.
Is it feasible?

Enabling the GPO output should not increase the power consumption, except when an interrupt is active, and GPO is driving a load. Here, with value 0x11, only Filed change interrupt is enabled. Do you have RF field present?

Best regards.

[Alex_B]

Hello,
Unfortunately it is not feasible to measure the current on the VCC_NFC only
There is not RF field present as I am not getting any interrupts to the MCU.
Thanks,
Alex

[JL. Lebon]

Hello, 

One more question. Why having a separate VCC_NFC power supply for the ST25DV?

Actually, the role of the LPD is to decrease poser consumption on the VCC pin. so there is no need to have an extra power supply specifically for the ST25DV. It can be connected to the main VCC signal.

You said: "the current draw goes up to 170uA even if the LPD is set to high and the VCC is set to low". Do you mean that you set LPD high and VCCPNFC low at the same time? There is no need, VCC can remain, only LPD needs to be set low to enter low power mode.

I still don't see the relation between power consumption and GPO. Is GPO output connected to anything ? If yes, can you disconnect it ?

Best reagards.