TPS62740: Excess current

Hi Terry,

I could not understand your problem clearly. Could you please rephrase your question?

Regards,

Febin

We found that there is extra current (varying from +2mA to +10s' mA) at the regulator even at its sleep stage.  The extra current can almost always be resolved by replacing or reflowing the regulator. The issue could relate to our layout. My guess is that there are short circuit (from the pads under the chip or) between some pins or some damage to the chip. However there still was proper output voltage from the "problematic" regulators though. That's why we need your insight to help us to improve our design so the issue can be avoided. Thank you.

Hi Terry,

I understand that you see excess input current drawn (varying from +2mA to +10s' mA). I would be curious to know about your measurement setup and exact probing points. 

Please specify all the conditions like Vin, Vout, Iin, Iout, etc. when you measured. It would be also better to measure SW node before and after the IC is replaced with the same conditions. Please share all the measurement results and we can analyse further.

Regards,

Febin

Hi Terry,

Do you have some updates to share?

Regards,

Febin

Hi Febin,

We measured the current at input power (between two pins of the SWITCH1). The battery voltage VBAT is at ~ 5V (could drop down to 3.5V). The regulator output is at 2.9V (Vcc, probed at VCC1). Load current varies from 100 mA to 10 uA for a transceiver. For the most of time, the transceiver is at sleep state, ~ 10uA. In this case, the transceiver was still working except that the battery run out quickly due to the extra current drawn. Let me know if you need anything else. 

Terry.

Any feedback on this?

Hi Terry,

Ideally, you should measure the current through D1. SW1 is not the correct probing point to understand the IC input current.

Could you tell me the part number for the fuse? 

Please share the scope plots for Vin, Vout, Iin, Iout.

Regards,

Febin

Hi Febin,

Yes, D1 is a better probing point then SW1. However, under normal operation, the Q2 is in off state. The fuse part number is 0ZCK0035FF2G. To me, the regulator's extra current (could be mA to 10s mA) is very likely due to the regulator IO line short circuit or something. The pcb layout of the regulator could be the cause it got damaged easily. Could you take a close look at the layout and let me know your insight? I believe your experience with this regulator could help us to improve the design. Thanks you.

Best,     

Hi Terry,

I am currently out of office and will be back mid of next week. I will check the layout and update you by end of next week. 

Thank you for your understanding.

Regards,

Febin

Hi Terry,

I looked again into the schematic and layout. 

1. The layout shows pnly the IC, please provide a complete layout including the passives.

2. The fuse should go on the other side of the input capacitor. So my first suggestion is to consider changing the position of the fuse.

3. Ideally the current through D1 should then be measured. This is the input current of the device.

4. Please share the measurement plots for Vin, Vout, Iin, Iout. May be I can analyse better. 

Regards,

Febin

Hi Terry,

Do you have some updates to share?

Regards,

Febin