LM5050-1: vgs not increase

user5368470

Part Number: LM5050-1
Other Parts Discussed in Thread: CSD19534Q5A

hi,

used the lm5050-1, and copy the typical application,but the vgs still 3.67V when VIN=5V~30V, Iload=0~7A. the mosfet is csd19534q5a, so that the mosfet is not completely opened, please help me to how to increase the vgs, so the mosfet would be opened completely.

best regards.

over 5 years ago

0 Karikalan Selvaraj over 5 years ago

TI__Genius 16305 points

Hi

LM5050-1 Regulates the Vds to 20mV by controlling the Vgs voltage of the FET. For lower load currents, Vgs will be low and for higher load currents Vgs will be high. CSD19534q5a is a 14mohm FET and for this FET above 2A, Vgs should be high >6V.

Can you please share the PCB layout of the IN and OUT pins.?

Regards,
Kari.

0 user5368470 over 5 years ago in reply to Karikalan Selvaraj

Intellectual 530 points

dear Kari,
With very best wishes for you, Happy New Year! please down load the sch and PCB;

1. Iload=1~7A load , the VGS always still is 3.88V, no increase. then the VSD almost 22mv. why vgs no higher?

2. how does the lm5050-1 driver current ？the CSD19534Q5A need Ig=Qgs/(tr+td)=5.1/(9+14)=0.222A, but the datasheet of the lm5050 note the Ig is 32uA, so I just confused the driver current.

best regards.

lm5050_csd19534.rar

0 user5368470 over 5 years ago in reply to Karikalan Selvaraj

Intellectual 530 points

hi Kari,

how does the lm5050-1 driver current ？the CSD19534Q5A need Ig=Qgs/(tr+td)=5.1/(9+14)=0.222A, but the datasheet of the lm5050 note the Ig is 32uA, so I just confused the driver current.

0 Karikalan Selvaraj over 5 years ago in reply to user5368470

TI__Genius 16305 points

Hi

Altium PCBdoc is missing in the attached rar file.
Can you please resend it.

I dont see any issues with the schematic, but need to have a look at the layout to debug.

The calculations you have shared are mainly applicable for fast gate drivers used in switching regulator applications where the gate drive is very fast.

Here, the gate drive is slow and controller to drive the ORing MOSFET.

Regards,
Kari.

0 user5368470 over 5 years ago in reply to Karikalan Selvaraj

Intellectual 530 points

hi Kari,

please reference the following file, I have understanded the gate driver . thanks.

my design requirements： Iload=0~7A, I wanna to change the ORing MOSFET , change the Rdson ( 14mohm) to 6mohm. ok?1122.lm5050_csd19534.rar

0 Karikalan Selvaraj over 5 years ago in reply to user5368470

TI__Genius 16305 points

Hi

I still don't see the .pcbdoc file, please attache the .pcbdoc file along with .schdoc file and .prjpcb files.

Regards,
Kari.

0 user5368470 over 5 years ago in reply to Karikalan Selvaraj

Intellectual 530 points

dear Kari,

Once you have downloaded this file, extract its contents, you can see the .pcbdoc file, and .schdoc file .6371.lm5050_csd19534.rar

0 Karikalan Selvaraj over 5 years ago in reply to user5368470

TI__Genius 16305 points

Hi,

I extract the contents of the file, still i don't see the .pcbdoc file.

Regards,

Kari.

0 user5368470 over 5 years ago in reply to Karikalan Selvaraj

Intellectual 530 points

dear Kari,

I am so sorry to upload the wrong file, now please see the new file.2117.lm5050_csd19534.rar

0 Karikalan Selvaraj over 5 years ago in reply to user5368470

TI__Genius 16305 points

Hi,

I have looked at the schematic and PCB file.

There is one recomendation: reduce the PCB trace length from MOSFET drain to OUT pin as indicated in the picture attached.

For 7A application, choosing a 6mohm MOSFET is good.

However, note that LM5050-1 does regulation of Vds voltage to 22mV by controlling the Vgs voltage.
So expect lower Vgs at lower currents and higher Vgs at higher currents.

Let me know if you have more questions.

Regards,
Kari.

0 Karikalan Selvaraj over 5 years ago in reply to Karikalan Selvaraj

TI__Genius 16305 points

Attached the picture now.

Regards,

Kari.

0 user5368470 over 5 years ago in reply to Karikalan Selvaraj

Intellectual 530 points

dear Kari,

so happy to receive your reply, and I agree with your recommend about PCB layout . thanks very much.

best regards

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LM5050-1: vgs not increase