ISL81601 UPS with low voltage battery/capacitor

Hi, 

What's your output /load requirement  (v& I). 

Figure 3 shows the four-switch buck-boost converter operation modes and waveforms controlled by the ISL81601. When Vin is lower than Vout, it runs in boost mode, as shown in Figure 3C. When Vin is higher than Vout, it runs in buck mode, as shown in Figure 3A. When Vin is close to Vout, it runs in buck-boost (one cycle buck followed by one cycle boost) mode as shown in Figure 3B .   

Also As per flow of charge & discharge . Vin  to Vout is buck converter  & Vout to Vin boost converter . If you connect battery at output side you will get boost voltage at input side . & vice versa.

Thanks 

AB 

Hi,

Charge current is 3A, max. battery voltage is  between 4.2V and 2.7V. System current is 3A, system voltage is 5V.

Br,

Zoltan

Hi,

We have built the ups with ISL81401 with 12V system bus. It is charging the battery without any problem, but not doing the 12V from the battery, when  we are removing the power supply, so not working backwards. I have checked the mosfet gates, but there is no pulses in case of backwards direction.

Any suggestion, what we have to check?

Thanks for help in advance.

Br,

Zoltan

Hello, Zoli! I'm glad there is feedback.
Now I have created a project 12V source - IS81601 - 4S7P battery from 10V-16V (the battery is hanging on the output of the microcircuit). I am waiting for the components and will include this board.
Zoli, tell me the parameters of the circuit. Is the input of the microcircuit hanging on the main 12V line? and the battery is hanging on the output of the microcircuit?
What kind of battery do you have? What is the battery voltage range?
As I understand the operation of the circuit - (if the main 12V and the load are from the input side of the microcircuit, and the battery is on the output side) - then when the main 12V (at the input) disappears, you need to force the GM2 circuit to change the direction of energy (from the battery towards the main 12V). That is, you need to select a divider for the GM2 circuit slightly below 12V.

Hello Korg!

Thanks for the answer.

Yes, the input is connected to the main 12V line, and battery is to the output. Actually battery is a single LIFEPO4 one (2.5-3.6V), but can be upgraded to 2S or 3S. Instead of ISL81601 we have used ISL81401, as 40V limit is high enough. Ru is 620k, Rd is 47k, calculated voltage on input is 11.35V.

On test  PCB we used 4 mosfet (Q1-Q4), but actually there are only 2 implemented (Q1 and Q2), as it is purily a buck converter (and boost in reverse direction). Q4 is shortcircuit, and Q3 is open.

In reverse mode there is 2.8V on input side, battery is 3.2V,  LG1 is steady 0V, UG1 is steady 3.2V (tested on oscilloscope). It looks the controller relucting to do its job is the direction. There is no load on the system, only the multimeter.

Br,

Zoltan

Try playing (putting a variable resistor) on the FB-OUT divider. Create a condition where the Battery Voltage is higher than the FB-OUT setting
With the correct bias of the current sense op amps in the ISL81401 controller, it can sense and control both positive and negative currents at both the input and output. This is important for reliable operation of a bidirectional DC/DC converter.
A bidirectional DC/DC converter requires control of the input/output voltage and current.
That is why it is important to be able to adjust the Input and Output voltage dividers.
Can you send me a schematic of your project?

[email protected]

Hi!

Fortunatelly we could find the solution.

Chip was in "DEM" mode (MODE pin was forced to "High"), which have  blocked the reverse mode.

Actually we have a new problem. In reverse direction the output voltage is 11.3V. If we increase the load, around 0.9A, the voltage start to decrease significantly, at 1A it is only 9V.

Battery voltage is 3.15V. What can be the problem?

Br,

Zoli

Hello! Interesting point. Your voltage drops under load, are you using only one battery? Additionally, install electrolytic capacitors on the output and input. Perhaps you do not have enough power from one battery?

Hi korg!

We have added a 470uF electrolytic on the input side. Also decreased both shunt resistors, just for checking, same result. We have tested with full and almost empty battery (3600mA), no difference.

Adding extra bulk capacitor on the output side is a good idea. I have just checked it. Added and extra 220uF one, but problem is still exist.

We will also check 2S1P battery configation, but it is not really a desired configuration, as we need and extra balancer circuit.

Br,

Zoli

Good day!
How are you doing with the problem?
Have you found a solution?

Hi Korg!

Actually no solution yet.

New problem has been realized meanwhile. When the battery is fully charged (~3.5V on LIFEPO4), reverse mode is ok, but if the battery voltage is lower, controller is  not switching to reverse mode automatically. 

I can imagine, that the root of all problems are the same.

Br,

Zoli

Hello, Zoli!
I assembled my board, trying to launch it. I have problems too.
Tell me how are you doing?
Have you solved the problem with the output voltage of 9 volts with one battery (~ 3,5 В на LIFEPO4)?

Hello, Zoli!
I assembled my board, trying to launch it. I have problems too.
Tell me how are you doing?
Have you solved the problem with the output voltage of 9 volts with one battery (~ 3,5 В на LIFEPO4)?