My Question to TI

Does the VSTOR Pin provide output voltage in the absence of the VIN BUT in the presence of a Storage element.? NOT!

Introduction

I finally got around to testing the BQ25504 and it was not what I expected but I am stupid so its all good.. I assembled the required circuitry and connected my solar panel and super cap and expected the output to be reasonably 5V. Unfortunately it was not. I am going to do a flashback on what I designed and then a little on what I got.

Flashback

I started with a schematic in Eagle that looks like this...

I did an entire post on the matter at [Firecracker Analyzer] Making the Power PCB with Eagle, TI BQ25504, TPS62740 and TPS61200 In this instance, I only mounted the BQ25504 part for testing and instead of connecting a battery, I connected a 0.1F(not uF) capacitor as my storage element.

The results

The solar panel can produce voltages around 2volts in low light and up to 5volts in direct sunlight. For test purposes, I connected it to my bench power supply and set it to 1.9Volts. The boost converter came alive and punched out 3.7Volts at the output and the capacitor began to charge. I connected a Tektronix Scope to the output and it was captured as follows.

It is seen that the capacitor charges to 3.96Volts and then the output steadies. Once I switch off the power, the output ramps down. Good right? Wrong. This waveform is for the output voltage and without any load other than the Scope. This means the output will be valid only until there is an input from the solar panel. The vstor output is used to drive things when there is solar panel input and if it goes down, it will NOT connect it to the storage element.

Furthermore, when I switch on the Vin, the output jumps up directly to 3.96Volts which means my Cap is already fully charged. The capacitor is rated at 5.5V and the voltage to the terminals is 4.08V and keeps steady even after I have switched off my supply or solar panel. Hence what I am SUPPOSED to do is to use the battery/capacitor directly. I can then use my buck and boost converters to create the voltages I like. Fancy that!. I have the buck converter already connected to the VBAT so my 3.3V should be painless.

The boost converter is however connected via the VSTOR which means it will provide stable 5V only when there is a solar pannel power generation. I may be doing something wrong here but this is what I have got!

Next steps.

I need to mount the buck converter to create the 3.3V for the launchpad and cut traces on the boost converter. I am going to assemble the boost converter on a seperate PCB and connect them together. Fingers crossed!