BQ24780S-EVM VSYS powing issue

Luke Duzanica7

Currently received the evaluation board for testing on performance for use in our design, yet while I hooked up all the equipment required to test per the user guide the VSYS connection is causing the ACOK led to become dim and pulse. With no load on VSYS, the system works fine. The input MOSFETS for the adapter seem to be working fine, yet Q3, Q4, and Q5 during diode testing to short for a few seconds before forward voltage is read. Is this normal per the layout for the eval board?

over 10 years ago

0 Wang5577 over 10 years ago

TI__Guru 56650 points

What is Vsys load current when the ACOK led becomes dimand pulse? At that time, what is the input voltage?

0 Luke Duzanica7 over 10 years ago in reply to Wang5577

Prodigy 110 points

The input voltage is set to 17.5 Volts, the Vsys load current drops to only 10 to 20 uA with Vsys output voltage shifting from 125 mV to 510 mV

0 Wang5577 over 10 years ago in reply to Luke Duzanica7

TI__Guru 56650 points

"With no load on VSYS, the system works fine. " If ACOK is high, you should see Vsys is same as the input voltage.
Do you have a user's guide? In user's guide, it has a short test procedure. Would you follow the test procedure and let me know the abnormal issue?

0 Luke Duzanica7 over 10 years ago in reply to Wang5577

Prodigy 110 points

Going through the user guide, all steps up to 3.3 step 1 show correct voltage levels when measured, when I do step 2 on 3.3, the ACOK begins to pulse and current and voltage levels on VSYS drop

0 Wang5577 over 10 years ago in reply to Luke Duzanica7

TI__Guru 56650 points

Ok. So, you already checked the charge enable on step 3.2 and saw a correct 12.6VBAT and 19.5VSYS.

On step 3.3, a 10.5V load is added to BAT first, not SYS. "Connect Load #2 in series with a current meter (multimeter) to J2 (BAT, GND)."
And then, add a load on VSYS.
Do you add BAT load or SYS load when ACOK begins to pulse?

0 Luke Duzanica7 over 10 years ago in reply to Wang5577

Prodigy 110 points

I added BAT first and no pulse, once SYS was added it began to pulse

Power management

Power management forum

BQ24780S-EVM VSYS powing issue