how to use an LT1618

[hoopa]

Hello,

For a project I have to use an lt1618.
My Vin = 4V with 1.1A and I want to convert that to Vout = 5V in 0.6A.

I first used this design and with the right R1 and R2 i'm able to get Vout =5V but the issue is i can't regulate my current at all, i'm getting Iout=Iin.

I'm guessing i'm using the wrong design.
Can anyone help me and tell which application is the i need?
Here a link to the datasheet.

--- Updated Apr 28, 2022 ---

https://www.analog.com/media/en/technical-documentation/data-sheets/1618fas.pdf

 

[KlausST]

Hi,

Yes but my input voltage variation isn't that big I don't think it will cause an issue.

You think .. but you should know. We can't help you with this because we don't know the requirements.
The given input variation is more than 10% .. and I expect the output current variation in the same percentage. For the very most of my designs even 1% would be too high an error.

Klaus

 

[hoopa]

Hi,

You think .. but you should know. We can't help you with this because we don't know the requirements.
The given input variation is more than 10% .. and I expect the output current variation in the same percentage. For the very most of my designs even 1% would be too high an error.

Klaus

Indeed i didn't test everything yet so i can't be sure.
My system isn't required to be extremely precise, my biggest issue is autonomy.
If I had to take everything into account I would also have calculated the changes when my LED heats up.


And about the mosfet before the IC controlled by the on/off controller, is it a good idea?

I will try to gather the max infos and and do all the calculations before Monday so i can be ready and test everything.

 

[KlausST]

Hi,

Indeed i didn't test everything yet so i can't be sure.

No need to test or calculate.
What I call "requirements" is like the destination of a travel. You first need to know where to go. Then you can decide how you get there. A train may be good idea ... but not when you want to travel to an island.

The same is with the Mosfet. In most cases it is a good idea. So yes, try it.
... but in detail it depends on what exactly you want to achieve.
Example:
Switching On/Off LEDs may be used for dimming ... then I'd use the switch at the output
Switching On/Off LEDs may be used for power saving (night / day) ... then I'd use it at the input of the regulator

Klaus

 

[cupoftea]

And about the mosfet before the IC controlled by the on/off controller, is it a good idea?

As Klaus implied, you can put an NFET in series with the LEDs...and just turn it ON/OFF

--- Updated Apr 30, 2022 ---

Also, attached is a LT1618 in buckboost mode, so you dont need a fet turn off

--- Updated Apr 30, 2022 ---

HV9910B is also a nice simple way of driving leds

https://ww1.microchip.com/downloads/en/DeviceDoc/20005344A.pdf