Decrease Vin on BQ25504

Franck DEGREMONT

Other Parts Discussed in Thread: BQ25504

Hi,

We wants to know how we can decrease the minimum Vin (voltage)? On wich component can we “play” to test a Vin under 110mV?

Second question, on the EVM card the cold start is at 330mv and after we can decrease the Vin voltage to 70mV and the card continue to perform (the DC DC boost function is already OK). We did the same card, but we change some resistors value for UV, OV, OK. But on our card the cold start is good at 330mV but when we decrease the Vin voltage (under 330mV) the BQ25504 stop… So Why the EVM card can start at 330mv and continue to works until 70mV and not our? Which element we have to change or increase?

Thnks for your help!! I become crazy!!!

F. Degremont

over 8 years ago

0 Jing Zou over 8 years ago

TI__Mastermind 19820 points

1. For bq25504, the minimum operating input voltage is 130mV. It is designed internally, so you cannot adjust it.
2. The device enters cold start when VSTOR voltage is under 1.8V (typ). I am not sure i understanding your description. Again, the minimum operating input voltage range when the device is out of cold start is 130mV. We cannot warrant any operation out side of the datasheet spec.

0 Franck DEGREMONT over 8 years ago in reply to Jing Zou

Prodigy 50 points

Thanks for your answer Jing Zou,

My problem is when I start the BQ25504, I need a pick at 330mv to start the component and it works with a voltage above 330mV but not under. When we test the EVM card (build by TI) we need a pick at 330mV and after the component works at 110mV and above. But not our card... We don't understand why... I measure the Vstor on our card it is at 2V directly (maybe more, like usualy, 3V), so we don't have the cold start.

thanks for your help.

F. Degremont

0 Jing Zou over 8 years ago in reply to Franck DEGREMONT

TI__Mastermind 19820 points

Again, for bq25504, the electrical characteristics table in the datasheet page 6 shows the minimum VIN(DC) is 130mV not 110mV

Can you please provide scope shot on VIN_DC, VSTOR, VBAT, and LBOOST of the "not working" scenario? Please provide more detailed description on what you refer as not working. Thanks.

0 Franck DEGREMONT over 8 years ago in reply to Jing Zou

Prodigy 50 points

Hi and happy new year,

Thanks for your answer,

This the screen shot with the EVM Card (by TI),

1=> Vin

2=> Vbat

3=> Vstor

4=> VLbst

As you can see on this screen shot, the component start à 330mV (340mV) and can works with a lower voltage like 70mV

This is the screen shot for our card :

As you can see, with our card the component start à 304mV and stop at 304mv. It cannot works like the EVM cards under 304mV and we are very far from the 70mV measured...

We would like to know why there is this difference.

This is a picture of our card :

Thanks for your help.

F. Degrémont

0 Jing Zou over 8 years ago in reply to Franck DEGREMONT

TI__Mastermind 19820 points

Comparing your VSTOR voltage in both scope capture. With the test on our EVM, the VSTOR voltage is around 2V, which means the IC is now in main boost mode. However, in your second scope capture, the VSTOR voltage is clearly lower than 1.8V. This means the IC is in cold-start mode. In cold start, the input voltage needs to be at lease 330mV (typ) to start boosting as stated in the datasheet.

0 Franck DEGREMONT over 8 years ago in reply to Jing Zou

Prodigy 50 points

Thanks,
This is the problem, on the EVM card the Visitor is quickly at 2V or more, but not on our card. But I don't know why, because we have two capacitors one at 4,7µF, and an other at 0,1µF like the EVM card. We test to increase the capacitor with an other one 4,7µF in parallel, but there were no changes.
We make an other test : put directly 2V on VStor to load capacitors, and there is exactly the same comportment, we cannot decrease Vin under 304mV. So if you have an idea that what we can change to make some test and improve our card that will be (very) nice.