• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 1460 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.

BQ24773 - Different between rev a and b EVM

Massimiliano De Cristofaro
Expert 6640 points
Other Parts Discussed in Thread: BQ24773

Dear team,

a customer of mine has the following question about the EVM of the BQ24773.

The original eval board schematic showed a diode between pins 24 and 25 (D50 in snippet below):

On the later Rev B eval board schematic the diode is DNP (D1 in snippet below):

We made provision for a diode in this position and fitted it initially and all seemed good, but with the later advice that it should be removed we’ve taken it off and are now making two observations:

1.      At light load the output voltage is not what it should be

2.      At heavy load the output is unstable (sawtooth waveform)

 

There is a note in the datasheet that the bootstrap diode is integrated, which is presumably why the revised advice said it could be removed. Is/was there an issue with a certain revision of silicon that means the diode is still required? Does the strange behavior indicate some other parameter in our circuit is borderline? Any further revised data, possibly an updated datasheet (we have SLUSC03A dated August 2014)?

Could you please advice?

Thanks a lot in advance for your help.



Best regards,
Massimiliano De Cristofaro
Application Support Engineer - Power Management
ASKTEXAS DiamondLane – EMEA Distribution Support
Texas Instruments Deutschland

  • 0
    TI__Guru 56650 points

    Please give more detail info about the operation. Such as: What means "At light load the output voltage is not what it should be"? You don't have output voltage or output voltage higher, lower or just the ripple is bigger? What is the input and output voltage? What is charging current?

    That D50 is bootstrap diode to provide current path from REGN to BTST capacitor The external diode is a schottky diode which can reduce the voltage drop from REGN and BTST. So, at light load, the bq24773 doesn't need to frequently turn on the LODRV to charger BTST capacitor. The internal diode can't be a schottky which has a high voltage dop and requests more LODRV pulses to charge BTST capacitor at light load.

    For heavy load, what is your input and output voltage. If input is very close to output, the LODRV refresh pulse for charging bootstrap capacitor could also make the output ripple waveform looks different. 

  • 0 in reply to Wang5577
    TI__Expert 6640 points
    Hi Wang,

    thanks a lot for your support.

    I sent this information to the customer.

    Thanks again.

    Best regards,
    Massimiliano