Startup issue ADP5090

Question

Hello all, 
 I'm having an issue with the ADP5090 startup sequence with some of my PCB's. Some of our PCB's came back not working. I use the ADP5090 to charge and manage a small 25 mAh Lithium polymer battery and use RFID Vout to as Vin for the ADP5090. This works fine on most of the PCB's but some the ADP5090 never achieves a stable SYS voltage as shown in the measurement below: 
 
 Note: Voltages are a bit higher than in real life due to max setting on scope. 
 More zoomed in on the issue. SYS reaches a good voltage but than collapses back to the End of Cold-Start Operation Threshold. 
 
 This is the schematic used: 
 
 Hope anyone can point me in the right direction of this issue. 
 Thanks, 
 Michael

ADIApproved · Accepted Answer

Hello Michael, 
 the problem should be SETPG and SETSD same or too close. When the PGOOD is high, ADP162 will startup and the SYS and voltage will drop so that the SYS and BAT connection will turn off. The correct method is the set a higher SETPG to cover the droop during the ADP162 startup. 
 Regards, 
 Kevin)

ADIApproved · Answer

So far we don't have the simulation model. If you have any question, you can post it here.

ADIApproved · Answer

You're welcome. The ADIsimPE model may be not exactly matched with the real circuit but it's helpful to understand the behavior of this product. You can refer to the typical circuit of the datasheet.

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Startup issue ADP5090