TPS65186: damage case

Hi Brandon,thank you for your replay. Per 7.1 of datasheet, Abs min voltage is VCOM_PWR,not VCOM.

As VCOM is out pin, before device power up the -100mV is not allowed？

This problem has appeared on several boards, so we want to clarify the cause。

Hi Guigao,

  I think it should be ok for VCOM pin with -100mV before device power up. I'll let the device expert answer you next week. 

Thanks!

Phil

Hi Guigao,

1. How are you confirming the TPS65186 is damaged in this scenario?
2. Does discharging the -100 mV at VCOM before power up prevent this damage?
3. Can you explain the TPS65186 operating conditions when -100 mV is present at VCOM?
4. In addition, what are the voltages at these pins?

• VIN
• VIN_P
• WAKEUP
• PWR_UP

Thanks,

Gerard

Hi Gerard

1.How are you confirming the TPS65186 is damaged in this scenario?

A:VPOS/VNEG does not have normal output and after replacing the chip the output is normal .

2.Does discharging the -100 mV at VCOM before power up prevent this damage?

A: We do not have the discharging circuit on the VCOM.  If  the -100mV is the cause of the damaged chip, we will avoid it.

We want to know the reason.

3.Can you explain the TPS65186 operating conditions when -100 mV is present at VCOM?

A: At the beginning TPS65186  is not powered when -100 mV is present at VCOM.

  and then, +5V is powered with as the following circuit.

4.In addition, what are the voltages at these pins?

A：Before TPS65186  powered
 VIN ：0V
 VIN_P：0V
 WAKEUP：0V
 PWR_UP：0V

After TPS65186  powered
 VIN ：+5V
 VIN_P：+5V
 WAKEUP：+3.3V
 PWR_UP：+3.3V

HI Guigao,

Thanks for sharing the additional details. For (2) is it not possible to discharge with an external pull-down resistor?

We are trying to understand if applying -100 mV at any time causes the damage, or it if is sequence related (for example, the damage only occurs if -100 mV present and input power is applied). A scope shot demonstrating VCOM, VIN, WAKEUP, PWR_UP would also be helpful for this. 

Regarding the schematic:

• Boost inductor (L1) should be 2.2 uH
• Inverting Buck-Boost inductor (L2) should be 4.7 uH
• A local 4.7 uF decoupling capacitor is recommended at the VCOM_PWR pin

Is it possible to correct these and test if the issue still occurs?

Thanks,

Gerard

Hi Gerard

Thank you for your suggestions and corrections to the schematic.

Since the board has already been delivered to the customer, we can't test it right away.

Can you tell me VCOM -100mV (minus voltage) input is the guaranteed operating range for TPS65186 or not ?

Thank you！

Hi Gerard

Are the following recognitions right?

Any voltage applied to the VCOM pin at any point, It is not guaranteed that the chip can operate normally.

 *I think we can avoid  the -100 mV,so i want to resolve my issue.

Hi Guigao,

Your understanding is correct.

Thanks,

Gerard