LM5146-Q1: How to add over current protection for a particular current

Dinesh Gread1

Part Number: LM5146-Q1

Hi TI,

i am using a Buck converter using LM546-Q1 .I have design for 8 amp out, for 13.5V

Input 30-60V input .

i am using RDSon for current limit sense . But in the datasheet it is not clear how ILIM pin save the circut for overcurrent protection please explain.

. The issue i am facing with surge current.it is working fine while i am incresing the current from 0-1-2-3---8 up to 8 amp but while i am suddenly add load the circut went to hiccup mode as like short circuit.

Please let me know how to resolve the issue,

Is the anyway i can limit the current for 10 amp max?

if i will use ILIM pin for 10amp limit the current, curcuit not able to take surge current. Please provide some suggestion .

over 5 years ago

0 Arief Hernadi over 5 years ago

TI__Mastermind 23845 points

Hi Dinesh,

Unfortunately, I was not able to see the component values for the schematic that you have.

You can check the component selection values with the calculator located at the bottom of this page

http://www.ti.com/product/LM5146-Q1/toolssoftware

Also the layout will play an important role in order to sense the current limit correctly. You can follow the layout guidelines here

http://www.ti.com/lit/ds/symlink/lm5146-q1.pdf#page=48

Thanks

-Arief

0 Dinesh Gread1 over 5 years ago in reply to Arief Hernadi

Prodigy 140 points

Hi Arif,

Please explain How ILIM pin works?

also please let me know how to switch off the converter if someone tries to take more current ? for example i have design the converter for 8 amp if somone tries to take 10 amp i wants to switch off at that moment so please let me know your suggestion.

do i need to add another opamp or use another technique.

Thanks

Dinesh

0 Dinesh Gread1 over 5 years ago in reply to Dinesh Gread1

Prodigy 140 points

Hello Arif,

i am waiting for reply please explain .

Best Regards,

Dinesh Gread

0 Arief Hernadi over 5 years ago in reply to Dinesh Gread1

TI__Mastermind 23845 points

Hi,

I think the explanation of the current limit is located here

https://www.ti.com/lit/ds/symlink/lm5146-q1.pdf#page=23

I dont think the device will shutdown if the current limit is achieved. If you want the part to shutdown then you have to use maybe an external current sense amplifier and set it such that it will disable the part when the desired current is reached.

Thanks

-Arief

0 Timothy Hegarty over 5 years ago in reply to Arief Hernadi

TI__Guru 72622 points

Hi Dinesh,

The LM5146-Q1 will enter hiccup mode if the current limit condition persists. Once the current limit is removed, normal operation resumes.

Regards,

Tim

0 Dinesh Gread1 over 5 years ago in reply to Arief Hernadi

Prodigy 140 points

Hi Arif,

will you please suggest any circuit which i can use for current limit.

Best Regards,
DInesh Gread

0 Arief Hernadi over 5 years ago in reply to Dinesh Gread1

TI__Mastermind 23845 points

Hi Dinesh,

The inrush current is it due to charging to the output capacitor? If that is true then you can use a larger SS capacitor and slow down the rise time of the output such that the inrush current will not be too big and trigger the current limit

Thanks

-Arief

0 Dinesh Gread1 over 5 years ago in reply to Arief Hernadi

Prodigy 140 points

Hi Arif,

i have made this circuit for 8 amp out. i want this circuit to limit the current at 9-10amp more than that it shoud not provide. the short circuit condition is fine it enter in hiccup mode but i want that if i design this circuit for 8 amp it should not provide more that that .

can you please suggest any circuit by use of that i can limit the current .

Also please let me know how to reduse the no load current currently the circut works on 400Khz and take 40ma and it is just waste can you please let me know how to minimize it.

i dont have control on EN pin i.e this circuit will not off any time but load can be off so that i wants to reduse the no load current also. please suggest

0 Dinesh Gread1 over 5 years ago in reply to Dinesh Gread1

Prodigy 140 points

Hi TI Team,

i am waiting for your inputs .

Best Regards,

Dinesh Gread

0 Timothy Hegarty over 5 years ago in reply to Dinesh Gread1

TI__Guru 72622 points

HI Dinesh,

You can use diode emulation mode (with SYNCIN tied low) to reduce the no-load input current.

In terms of overcurrent protection (OCP). the setpoint is typically defined using the ILIM resistor at 130-150% of nominal full load current. This is because the inductor current overshoots during load transients and may inadvertently trip OCP. Please fill out the LM5146-Q1 quickstart file and send to us for review. Also, the schematic values above are unreadable, so please forward a higher res version if possible

PS: Your design seems similar to the LM5146-Q1 EVM with 12V/8A output.

Regards,

Tim

0 Dinesh Gread1 over 5 years ago in reply to Timothy Hegarty

Prodigy 140 points

Hello Tim,

Thanks for the reply.

1. For no load current i have left the SYNCIN open so it can be go into diode imulation mode.(As per datasheet it can left open) but still take 40mA.Please let me know if i am doing something wrong,

2. Query secnd is i have design the converter for 8 Amp and over current protection will take place at 12 Amp(120-130%Load) to go into hiccup mode. i need the converter should not provide that any extra current more than 8 Amp continous or it shoud limit at 8Amp . Hiccup mode is fine while i will short circuit and it is working fine in the current cuircut.

if the picture not clear please let me know i will try to get the clear sch file tomorrow.

0 Dinesh Gread1 over 5 years ago in reply to Dinesh Gread1

Prodigy 140 points

Please find the attached some part of schematic i will ask my team to send me whole file but at this time i have attached file only please let me know if any change required.4331.Sch.docx

0 Dinesh Gread1 over 5 years ago in reply to Dinesh Gread1

Prodigy 140 points

Hi Tim,

Please reply,

Thanks,

DInesh Gread

0 Arief Hernadi over 5 years ago in reply to Dinesh Gread1

TI__Mastermind 23845 points

Hi Dinesh,

I think Tim was referring to the user guide schematic as a reference for the design

http://www.ti.com/lit/ug/snvu591/snvu591.pdf

The compensation, and component values will be a good starting point to the design.

One thing that i note is that the Zener trace to VCC does not seem to be correct.

Here is also the link to the calculator

http://www.ti.com/tool/LM5146DESIGN-CALC

Thanks and i hope that helps

-Arief

0 Dinesh Gread1 over 5 years ago in reply to Arief Hernadi

Prodigy 140 points

Hi Arief,

i have followd same there is no much difference in the schematic and eval board. .

That trace for reduce the power desipation in the iC because the out is 13.5V so i just pull it down 12V and given to VCC pin so the power dessipation can be reduce on the ic.

So please suggest more , please let me know if i reduce the frequency will it help me to reduce the no load current or do you have any other solution. Because it take 40ma just waste.

Thanks,

Dinesh Gread

0 Dinesh Gread1 over 5 years ago in reply to Dinesh Gread1

Prodigy 140 points

Hi Ti,

i am expacting reply in short time,you have more experience on your device more than us. each time i have to wait long to get your reply.

Request you to please provie someone email id to solve the query.

Thanks,

DInesh Gread

0 Timothy Hegarty over 5 years ago in reply to Dinesh Gread1

TI__Guru 72622 points

HI Dinesh,

Connect VCC to Vout through a series diode as shown in the datasheet. Then if the output experiences an overload or short circuit, it won't pull down the VCC rail. As requested, please send a completed quickstart file for this design so we can review stability and compensation values for this application.

Are there any other questions?

Regards,

Tim

0 Dinesh Gread1 over 5 years ago in reply to Timothy Hegarty

Prodigy 140 points

Hi Tim,

i have added the diode in physical board here in schematic it is missed.

I have attached excel file here also updated schematic as per physcial board.

Please tell me how to limit the current at perticular point without use of hiccup mode . i am using hiccup mode only for short circuit condication or it can be used only for that,

i have kept sync in pin open ( not connected to GND) as per datasheet it will go to diode emulation mode. than also do you recommended to keep syncin pin connected to GND.

Also let me know how to reduce no load current,

Please shre your thoughts,

0 Dinesh Gread1 over 5 years ago in reply to Dinesh Gread1

Prodigy 140 points

Hi Tim,

Attached file.

quick start.zip

0 Timothy Hegarty over 5 years ago in reply to Dinesh Gread1

TI__Guru 72622 points

Dinesh,

Thanks for sending the quickstart file. Just check that the output cap ESR is correct and that the compensation values align with what's in your schematic. Also, I see full-load current of 10A and current limit setpoint of 11A - this is too tight - you need at least a 30% margin as the inductor current exceeds the full-load level during a load-on transient.

If you need constant current (CC) operation, e.g. battery charging or LED lighting, I recommend adding a shunt on the output and a current sense amp and use that to control FB - more info here:

http://www.ti.com/lit/an/snva829/snva829.pdf

https://e2e.ti.com/blogs_/b/powerhouse/archive/2017/11/24/how-to-design-a-simple-constant-current-constant-voltage-buck-converter

Regards,

Tim

0 Dinesh Gread1 over 5 years ago in reply to Timothy Hegarty

Prodigy 140 points

Hi Tim,

Thanks for sharing the reference. i also have another idea to control the same i will share you soon,

Please let me how to reduce the no load current also. This is a big challenge for me at this time,it is now approx 40mA .

Thanks,

Dinesh Gread

0 Timothy Hegarty over 5 years ago in reply to Dinesh Gread1

TI__Guru 72622 points

Hi Dinesh,

You can check if the controller is folding back the switching frequency at light loads by looking at the SW node voltage.

Also, check the MOSFET part numbers so that the drive current requirement (Qg * Fsw) is low. Operating with external VCC (derived from Vout) can help here also, although the higher gate drive voltage, above the nominal 7.5V, increases gate drive loss.

Regards,

Tim

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LM5146-Q1: How to add over current protection for a particular current