Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

[SOLVED] ltc4020 charge current limiting

Status
Not open for further replies.
F

ferbo

Junior Member level 2
Joined
Feb 1, 2021
Messages
22
Helped
0
Reputation
0
Reaction score
1
Trophy points
3
Activity points
227
Hello everyone,

I am designing a charger power path manager with ltc4020. My input voltage is 35-50 v output is 40-50 volts. My output maximum current is 5 A and I have a 12s li-po battery.

this IC has a current sense resistor for the battery charging and two separate current senses for the inductor current. I am building my design based on the circuit on page 48 of datasheet.

My question is that how does this IC control the charge current while simultaneously supplying the load? Is it possible that that it controls the current that passes through the P channel FET connected between the output and the battery?

Thank you for your help guys.
 

A typical method for monitoring current is to measure voltage across a resistor in the current path. (Often a low-ohm resistor.) A control circuit takes this reading, and varies bias to a transistor such as you mention.
 
  • Like
Reactions: ferbo

    F

    ferbo

    Points: 2
    Helpful Answer Positive Rating
Hi,
ferbo said:
My question is that how does this IC control the charge current while simultaneously supplying the load?
Click to expand...
It depends how your load is connected.

More exactly:
As Brad says there should be a shunt to measure the charging current. It depends at which end of the shunt you connect the load.
In one case it sees just the battery current (true charging current)
In the other case it sees "battery current + load current".

You have to provide more detailed informations about your complete application:
At least
* charging circuit ( as black box)
* shunt of charging circuit
* load (as black box)
* battery
* and how all these things are wired

Klaus
 

Thank you all. The controller that you can see in my basic picture monitors the total input current and the charging current using sense resistors. I understand that it can control the total converter current using the switches dedicated to the DC/DC converter. But that is not my problem. My issue was how it controls the charging current separately. Which now I think is done by applying different voltages to the Vgs of the p-channel fet between the battery and output???
 

Attachments

  • block_1.jpg
    block_1.jpg
    656.2 KB · Views: 100

Hi,

In this case it's problematic. I thought the Mosfet and Shunt are interchanged.
The schematic now makes the charge current correctly, but the load (in non charging mide) has to run via the Mosfet's internal body diode which causes
voltage drop.

A schottky diode will reduce the voltage drop.

Klaus
 
  • Like
Reactions: ferbo

    F

    ferbo

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top