use ADP2360 as a current source

Hi ALIREZA7,

Thank you for your intention to use the ADP2360 as a current source. I think this is possible but the part was not characterized for this application. And the accuracy of the current source depends not only on the drift of the ADP2360 reference but also with the resistor drift across temp.

May I know your end application? I was thinking that you are going to use the ADP2360 as an LED driver, can you confirm? If that is the case you can check on our LED driver portfolio on this link. http://www.analog.com/en/products/power-management/led-driver-ic.html

Thanks and regards,

Jefferson

hi

my end application is electromagnetic flow meter. and i want a current source for coil excitation.

according to this article :

http://www.analog.com/en/analog-dialogue/articles/electromagnetic-flow-meters.html

analog devices suggested these two switching regulators for current source :

Table 5. Recommended Switching Regulators

Recommended ADI Switching Regulators Efficiency

ADP2441 90% at 200 mA output (@12 V), up to 1 A capable

ADP2360 90% at 10 mA output, up to 50 mA capable

in my design due to the arrangement and number of turns of coils i need a 20ma current source for coil excitation.

as ADP2441 efficiency is low @ 20ma so i decided to use ADP2360 . but now due to your statement it dosn't seem a right choice .

what is analog devices right solution according to my system requirements?

On Mon, Apr 2, 2018 at 11:08 AM, jeco <

Hi ALIREZA7,

As I've mention before the ADP2360 can be use for your application that give better efficiency at 20mA excitation current. I just need to check on the reference drift across -40C to 85C for us to estimate the excitation current drift. I'll get back to you on this.

Just a question, how do come up with the excitation current drift of 0.05mA (worst case) which is just 0.25% of the excitation current (20mA) which I think is too tight and I can't see any regulator that have the feedback/output accuracy of 0.25% (most is just around +/-1%). Perhaps this specs can be loosen.

If you got a chance, please check the Analog Devices current sources portfolio on this link.

http://www.analog.com/en/parametricsearch/11402

Perhaps one of these current sources will meet your drift specs.

Thanks and regards,

Jefferson

the excitation current drift of 0.05mA was calculated based on our specific flow meter error but it seems that we should reduce our expectations so 1% will be ok.

i would be grateful for check on the ADP2360 reference drift across -40C to 85C to estimate the excitation current drift .

On Tue, Apr 3, 2018 at 11:56 AM, jeco <

Hi ALIREZA7,

Thanks, I understand now where you get the your drift specs.

Fortunately I got the test data regarding the FB drift across -40C to 85C which is shown below (150 units tested).

With test conditions of -40C, 25C, 85C, and 125C, we can see a bow curve trend on the FB having the highest FB voltage at 25C which gets lower for -40C and 85C and much lower as the temp increases to 125C. 

However, as per datasheet, the FB voltage can be within -1% to +1.5% worst case across temp (up to 125C).

I think you also need to have low temp drift sense resistor to minimize the overall error in your system.

I hope it help.

thanks and regards,

Jefferson

thanks for your help.we got the point.

now our next challenge about using adp2360 as a 20ma current source , is

that it have a fixed reference voltage. it means that we should use a shunt

resistor : R=0.8V/0.02A=40R which is high for a shunt resistor and decrease

the efficiency. we think the solution is to use a <1R shunt resistor with a

current sense and tie the out put of current sense circuit to the FB pin of

adp2360.

i should mention that we need a uni directional low side current sense

according to

out design.

can you please give us any solution for a zero drift current sense circuit?

On Wed, Apr 4, 2018 at 1:06 PM, jeco <

Hi ALIREZA7,

Yes, the 40ohm shunt resistor will consume 16mW of power and reducing the shunt resistance should improve system efficiency by using a low voltage low drift current sense amp. Please check the ADA4582-1 (Precision, Ultralow Noise, RRIO, Zero-Drift Op Amp). You can also ask support regarding zero-drift current sense circuit in the amplifier community on this link. https://ez.analog.com/community/amplifiers. They might be able to give you even more recommendations.

Thanks and regards,

Jefferson