• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 351 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS7951-Q1: Sometimes read value is 5V

Suhyun Choi
Prodigy 20 points
Part Number: ADS7951-Q1
Other Parts Discussed in Thread: ADS7951

Hello.

There are some problems when I use read data from ADS7951 by SPI, and SPI baud rate is 500KBPS.

The application is battery management system and ADC reference is 2.5V.

Normally, all channels of ADC operate normally.

But, under certain circumstances, is operates abnormally(at the time of relay operation).

CRNT_H, CRNT_L, V_REF, V_VB are sensed as 5V.

In this situation, even if the ADC is initialized again, the result is the same.

In our system, there are two ways to power off/on the system.

1. Power on after REFP = 0V, VA/VBD = 0.7V.

The result is the same(CRNT_H, CRNT_L, V_REF, V_VB are sensed as 5V).

2. Power on after REFP = 0V, VA/VBD = 0V.

The result is normal.

Does the difference in VA/VBD voltage affect the ADC conversion?

The following is our code.

Please help.

Thanks.

  • 0
    TI__Mastermind 22950 points

    Hi Suhyun,

    Is Vref a constant 2.5V and under certain conditions, being read as 5V or are you applying 5V to Vref? The device is designed to operate with a reference voltage from 2V - 3V. If you are supplying a Vref of 5V, then I suspect that the unexpected behavior you are observing may be due to Vref being set to 5V. 

    If you are supplying a constant 2.5V to the device but it is reading Vref as 5V, then could you please share a schematic and elaborate on what "under certain conditions" means?

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    Prodigy 20 points

    Our schematic is as follows.

    In our schematic, VREF2V5 means constant 2.5V and VDA5V0 means constant 5.0V.

    Vref(2.5V) is connected to channel #6 of ADC7951 and reads 2.5V normally. 

    Occasionally an abnormal operation is performed(reads 5.0V) when the vehicle's high voltage(DC 700V) relay operates.

    "Under certain conditions" means this situation.

    Once this occurs, it persists even after turning the power off and on(ADC initialization does not work properly). 

    (The state when the power is turned off is REFP = 0V, VA/VBD = 0.7V)

    But, if the power off state is REFP = 0V, VA/VBD = 0.0V, abnormal behavior changes to normal behavior(ADC initialization work properly).

    Are VA/VBD voltage(0.7V) related to abnormal behavior(ADC initialization problem)?

  • 0 in reply to Suhyun Choi
    TI__Mastermind 22950 points

    Hi Suhyun,

    The device recommended operations is to have a minimum level of 2.7V on VA and 1.7V on VBD. It could be that the device is somehow latching when VA and VBD are 0.7V. I would recommend not to have the supplies at 0.7V if possible. 

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    Prodigy 20 points

    Thank you.

    We will review it further based on your comments.

  • 0 in reply to Suhyun Choi
    TI__Mastermind 22950 points

    Hi Suhyun,

    Thanks for note. I will close this thread for now. Feel free to respond and reopen the thread if necessary. 

    Regards,

    Aaron Estrada