Hi NXP Partner.
We follow the Vsense 3 circuit of RD9Z1-638BJBEVM. We measured the ripple voltage of C72 is about 1.7V.
Could we increase capacitance to 1uf ?
We have increased the capacitance.The ripple voltage becomes small.
Why is vsense 3 sink current huge to make the ripple voltage become big? It is normla behavior?
Br,
Mike Liang
Hi Mike,
Please see below the answer I received today from our BMS AE:
From my understanding of customer’s question, there is the voltage jump on Vsense3 pin.
First of all, from our LAB test result, the Vsense3 have no abnormal jump issue from my side. So I think this is a customer system noise issue.
From the schematic, the current leakage have two entrances to impact on Vsense3. One is Negative test point, another is VBAT+, we need to tell which one is the entrance, some suggestion as following.
1. Remove the D17 and disconnect the OPT-MOS, we can disconnect Vsense3 with GND by following these two actions. Then Vsense3 should equal to VBAT+. If the voltage jump issue still exist we can get conclusion the noise entrance comes from VBAT, if issue disappear we can get conclusion the noise entrance comes from VBAT+
2. If the noise comes from VBAT+(I suppose it is less likely since there is DCDC in VBAT), I think we can find out what is this noise comes from, maybe we can also increase the capacitor between VBAT VS GND.
3. If the noise comes from Negative test point, I suppose this noise may be comes from the Load. Customer can find what happened on the load.
Another question is the Vsense3 capacitance change from 22nF to 1uF, this change is good for voltage stability but not good for quick sensing since τ is increase. We need to balance the stability and reaction rate. Sorry I didn’t test with 1uF before, but I suppose the capacitor value a little bit higher.
Best regards,
Tomas
Hi Mike,
Please see below the answer I received today from our BMS AE:
From my understanding of customer’s question, there is the voltage jump on Vsense3 pin.
First of all, from our LAB test result, the Vsense3 have no abnormal jump issue from my side. So I think this is a customer system noise issue.
From the schematic, the current leakage have two entrances to impact on Vsense3. One is Negative test point, another is VBAT+, we need to tell which one is the entrance, some suggestion as following.
1. Remove the D17 and disconnect the OPT-MOS, we can disconnect Vsense3 with GND by following these two actions. Then Vsense3 should equal to VBAT+. If the voltage jump issue still exist we can get conclusion the noise entrance comes from VBAT, if issue disappear we can get conclusion the noise entrance comes from VBAT+
2. If the noise comes from VBAT+(I suppose it is less likely since there is DCDC in VBAT), I think we can find out what is this noise comes from, maybe we can also increase the capacitor between VBAT VS GND.
3. If the noise comes from Negative test point, I suppose this noise may be comes from the Load. Customer can find what happened on the load.
Another question is the Vsense3 capacitance change from 22nF to 1uF, this change is good for voltage stability but not good for quick sensing since τ is increase. We need to balance the stability and reaction rate. Sorry I didn’t test with 1uF before, but I suppose the capacitor value a little bit higher.
Best regards,
Tomas
