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ADP5090 Charging Problem

Question asked by Miaooo on May 5, 2017
Latest reply on May 8, 2017 by Kevin.Yao

Hello,

 

I am using APD5090 to charge a super capacitor from a mechanical harvester. The harvester generates a sin output with a frequency of ~1Hz, with max voltage amplitude of 2.5 V. I used a full-wave rectifier and a 4.7uF smoothing capacitor to rectify the input. I used CBP capacitor of 10 nF and MPPT ratio of 0.5.

 

The ADP5090 works fine in cold start region, and it is able to charge the super cap to 2 V. The problem comes when the boost charger started working.

 

1. According to the data sheet, the boost charger should sample the open circuit voltage every 19 sec by disabling the boost charger for 296 ms, and bring the input down to MPPT point. and this is what happened when I tested the chip with signal generator. However, with the mechanical harvester,  the boost charge first started working for 19 sec then it stopped working for many seconds (10-20 sec), in this period it is not charging the super cap regardless the input. Then after many seconds, the charger sampled the open circuit voltage again and started to charge the super cap again. All of these happened when the battery voltage is below protection circuit. Why it stopped periodically for several seconds?

2. During the period when the boost charger is not working, the sys pin tracks the battery voltage, if I connect a very small resistor to sys pin to drain it, it brings down the voltage at sys pin, as soon as the voltage is lower, the boost charger starts to work again. Why is this happening?

3. The input voltage after rectification does not stay constant even when the boost charger is not working. Is this due to he leakage of CBP or smoothing cap (I am using low leakage ceramic caps)? or it is due to the low frequency input?

 

Thank you very much,

 

Miao

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