MP2731 ADC reading and VNTC during discharging

Battery Management
1

Dear experts,

We are using MP2731 in our design. We have 2 questions:

  1. During discharging, are the ADC reading (system voltage, battery voltage, NTC) available or not?
  2. During discharging, is it possible to have VNTC pin voltage remain ON? So far as we tested and it went off as soon as Input voltage was turned off. I have tried searching on this forum but it seems there are 2 different opinions about this.

Thank you.
Regards,
Tuan.

2

Hi tuanpm519,

I’m looking into your question, will get back to you asap.

Thanks,
Cindy

1 Like
3

Hi Cindy,

Thanks, we are looking forward to seeing your response.

Tuan.

4

Hi tuanpm519,

If you take a read on page 26, underneath “ADC”, it states the ADC is only available in charge mode and OTG mode.
It looks like VNTC is regulated by an LDO that is powered from VREF. If there is no voltage on VREF, then VNTC will not be on.

Thanks,
Cindy

5

Hi Cindy, thanks for your response.

Regarding the ADC, this means during discharge if we want ADC reading we have to turn on OTG mode which we don’t want as it consumes more battery current. Anyways I understand this.

About the VNTC, from my testing I see that when VIN is not present and battery is discharging, VREF is still ON but VNTC goes off. Is there any register setting which we can use to turn it on?

Thank you.

6

Unfortunately, I couldn’t find anything that allowed VNTC to turn on during discharge/no VIN. Reading closely at the specs on the datasheet, it looks like VNTC only works when battery is charging and in OTG mode.

7

Could it be that one of the reserved bits in the registers independently controls the VNTC, so that it could be turned on during discharging? Could you speak with the actual designers (or refer to the HDL/logic) to se if such a bit exists?

8

Still awaiting reply from engineers working at MPS…

9

Apologies for the very delayed response. Since this post had earlier been marked as a solution, the priority of other active posts was the primary focus of our other engineers at MPS.

This post outline that VNTC is controlled by the LDO reference voltage, which deactivates during discharging unless OTG is an active mode where the user is trying to bypass this behavior without enabling OTG mode. Your question refers to a deeper look into the design reserved in the bits of these registers to see if they control VNTC discharging independently, correct?

If this is the case, I can address your questions directly by providing alternative ways for keeping VNTC on during discharge as we need to pick this up where we left off by asking if this question was and can be answered on our AE side.

  • Using an external LDO / Power Supply (it would independently control over VNTC power at the cost of that it would require additional components and trace design)
  • Using an always on Power Source of channeled bus (continuous power to VNTC without modifying IC very much at the cost of increasing power consumption complexity)
  • Enabling OTG Mode for a specified time and add time delays as needed for corrective sequencing (would use built-in functionality, but consumed more power when OTG pin is on)

I hope these are solid solutions to address solving the root cause as we are waiting on the AE side. If additional solutions are needed, please let me know. If you would like to escalate to the AE’s yourself, please submit a ticket to the following link: MPS NOW Remote Support - Support (monolithicpower.com)

Best,
Krishan

10

Hi, the OTG solution could have worked, unless I hadn’t hardwired the OTG pin directly to GND. So, I guess there is no way for the current design to access the NTC temperature sensor during discharge operation then - unless some of the reserved bits can be used?

11

VREF is always present. However, the whole ADC block is just not enabled when it’s operating from the battery supply. The pin-compatible MP2733 can enable the ADC during battery operation using the REG08 EN_ADC_DSG setting.