# Setting up a LT3478 current source

#### Domophone

Joined Sep 10, 2013
65
Hi Everyone,

I'm trying to set up an LT3478 current source. The output i'm looking for is between 5 and 25 Volts at 3.5Amps.

The alternative (because i don't know how i would deal with 20Amps@5V input via PCB) would use a 12V supply and go from 12V to 25V @3.5amps.

I've made a couple attempts to set it up using LTSpice, but i can't seem to get a boost factor of more than 2 out of the IC. Can anybody shed some light on what i'm missing here?

In the example LT Spice circuit I've attached, I have set the sense resistor so the output should be 3Amps (0.035 Ohm), however my output never goes past 2.04Amps.If I increase the Input voltage from 12V to 18V, it is suddenly able to output the 3 Amps i'm expecting. I couldn't find this input voltage limitation in the datasheet.

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#### ronv

Joined Nov 12, 2008
3,770
Hi Everyone,

I'm trying to set up an LT3478 current source. The output i'm looking for is between 5 and 25 Volts at 3.5Amps.

The alternative (because i don't know how i would deal with 20Amps@5V input via PCB) would use a 12V supply and go from 12V to 25V @3.5amps.

I've made a couple attempts to set it up using LTSpice, but i can't seem to get a boost factor of more than 2 out of the IC. Can anybody shed some light on what i'm missing here?

In the example LT Spice circuit I've attached, I have set the sense resistor so the output should be 3Amps (0.035 Ohm), however my output never goes past 2.04Amps.If I increase the Input voltage from 12V to 18V, it is suddenly able to output the 3 Amps i'm expecting. I couldn't find this input voltage limitation in the datasheet.

The current rating for the IC is the input current, not the output current.

#### Domophone

Joined Sep 10, 2013
65
hahaha, woops. Thanks!

#### ronv

Joined Nov 12, 2008
3,770