SN6505B: Current sensing on GND pin

Larry Gunseor

Part Number: SN6505B
Other Parts Discussed in Thread: SN6501

Need to know if it's possible to monitor current for the SN6505B transformer driver by putting a current sense resistor between Pin 4 and GND. If you do this does it effect the operation of the IC. If a resistor can be used between Pin 4 and GND, what is the max value that could be used. Looking to use a 1 Ohm resistor but could use a smaller value.

7 months ago

0 Prateek Verma 7 months ago

TI__Expert 3890 points

Hi Larry,

Yes you can monitor the current by using a current sense resistor between Pin 4 and GND. But make sure to use the resistor below 0.1 Ohm.

If you use 1Ohm then IR drop would be high which will affect the equivalent voltage across primary winding.

Let me know if you more question

Thanks,

Prateek

0 Larry Gunseor 7 months ago

Intellectual 360 points

Thanks Prateek, will give it a try.

Regards,

Larry

0 Larry Gunseor 7 months ago

Intellectual 360 points

Prateek, another question for you. I'm using the SN6501 SPICE model to do some simulations. It seems that if I put a 0.1ohm resistor from pin 4 and pin 5 to GND I don't see any signal across the resistor. Can you confirm this for me? Do you happen to have a SPICE model for the SN6505B device?

0 Prateek Verma 7 months ago in reply to Larry Gunseor

TI__Expert 3890 points

Hi Larry,

I think you would need to use amplifier to sense the current across the resistor.
Yes we do have SN6505B SPICE model - kindly find it in the product folder of SN6505B ( https://www.ti.com/product/SN6505B?keyMatch=SN6505B&tisearch=universal_search&usecase=GPN-ALT#design-tools-simulation )

Also if possible could you send me the Simulation setup that you designed for SN6501, I will also try to replicate this

Thanks,

Prateek

0 Larry Gunseor 7 months ago in reply to Prateek Verma

Intellectual 360 points

Prateek, trying to run the SN6505B in LTspice, it looks like the D2 and D1 are not going to ground when switching, any suggestions. I know you guys have PSpice for TI but prefer to simulate in LTspice.

0 Larry Gunseor 7 months ago in reply to Prateek Verma

Intellectual 360 points

Prateek, take that back looks like SN6505B takes around 4.9ms before it starts running. Will try it out and see how it works.

0 Prateek Verma 7 months ago in reply to Larry Gunseor

TI__Expert 3890 points

Hi Larry,

Let me know when you get results.

0 Larry Gunseor 6 months ago

Intellectual 360 points

Prateek,

I already have 49.9 ohm resistors in each transformer primary leg to reduce current and have a 1 ohm resistor from pin# 4 to ground. I'm running the transformer and the SN6505B off of +5V. I see approximately 100mA across the 1 ohm resistor. Everything seems to be working fine and I get a good signal across the 1 ohm resistor. Have a snapshot of the circuit but can't figure out how to attached it to the reply.

Also on the simulation model, if I place a 1 ohm resistor from the SN6505B pin# GND to circuit ground there is no signal across it. Not sure if there is anything they can doe with the model so that this works as the actual part does.

0 Prateek Verma 6 months ago in reply to Larry Gunseor

TI__Expert 3890 points

Hi Larry,

Good to know that you are able to sense the current with 1ohm resistor. You can send me the simulation files and snapshot of circuit with 1ohm res. on my email :- p-verma1@ti.com I will try to check what is the problem with the simulation.

Thanks

Prateek

0 Larry Gunseor 6 months ago in reply to Prateek Verma

Intellectual 360 points

Prateek,

Trying to send you the simulation but keep getting the message "couldn't be delivered". I have a .zip file attached to the email.

The error is below

Error:	550 5.0.350 One or more of the attachments in your email is of a file type that is NOT allowed by the recipient's organization.
Message rejected by:	IA3PR15MB6724.namprd15.prod.outlook.com

0 Larry Gunseor 6 months ago in reply to Prateek Verma

Intellectual 360 points

Prateek,

Send me an email and I'll reply back to it, maybe that will work.

larry.gunseor@generac.com

0 Larry Gunseor 6 months ago in reply to Larry Gunseor

Intellectual 360 points

Is there a site I can drop the files at then you can grab them?

0 Prateek Verma 6 months ago in reply to Larry Gunseor

TI__Expert 3890 points

Hi Larry,

If error is coming while sending it on email. You can send it here. Earlier there was issue while uploading file on this site, but this is now resolved.

Thanks,

Prateek

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SN6505B: Current sensing on GND pin