LM7481-Q1: C, VS, OUT protection

Joe Miller1

Part Number: LM7481-Q1
Other Parts Discussed in Thread: LM74500-Q1

Tool/software:

Dear Sir/Madam,

I am using the 2x LM74810QDRRRQ1 to drive a 24V two-speed motor.
The first LM74810QDRRRQ1 drives the speed1 wire when enabled.
The second LM74810QDRRRQ1 drive the speed2 wire when enabled.
The EN/UVLO pin is used to enable/disable the relevant LM74810QDRRRQ1.
I have found that the motor induces a voltage into the undriven wire.

(1) speed1 output is on, speed2 output is off
The motor induces a voltage into speed2.
Yellow is speed1 and green is speed2

(2) speed1 output is off, speed2 output is on
The motor induces a much larger voltage into speed1.
Yellow is speed1 and green is speed2

The datasheet specifies a maximum voltage of 70V for the C, VS and OUT pins with respect to GND.
Is there anyway to increase the maximum voltage rating or do I need to look for another solution.

Any comments and thoughts would be greatly appreciated.

Regards Joe

11 months ago

0 Shiven Dhir 11 months ago

TI__Mastermind 46120 points

Hi Joe,

Increasing voltage range at C,VS,OUT may not be possible.

Can you share schematics to analyze? Maybe some changes in schematic can help in decoupling this noise.

Regards,

Shiven Dhir

0 Joe Miller1 11 months ago in reply to Shiven Dhir

Intellectual 325 points

Hi,

Just want to get thoughts on increasing output voltage by either of the following.

(1) NMOS added with VDS rating of 200V and gate controlled by LM74810-Q1.
LM74810-Q1 will be enabled when driving speed1 and disabled when driving speed2.

(2) NMOS added with VDS rating of 200V and gate controlled by LM74500-Q1
LM74810-Q1 will be enabled when driving speed1 and disabled when driving speed2.
LM74500-Q1 is always enabled.

Regards Joe

0 Shiven Dhir 11 months ago in reply to Joe Miller1

TI__Mastermind 46120 points

Hi Joe,

You can use either of the two, did you try to evaluate on the board?

Functionalities wise it should be okay.

Regards,

Shiven Dhir

+1 Joe Miller1 11 months ago in reply to Shiven Dhir

Intellectual 325 points

Hi,
Thank you for the reply.
I have not tried yet.
My board is very small.
I just want to minimise risk and re-spin.
I am partial to just adding the NMOS due to space.
I will mod up something and try on the EVM.
Just want to confirm that when EN is 0V then OUT and HGATE will be 0V so
the NMOS will need a VDS to support the maximum voltage on VOUT which I measured as 70V.
Regards Grant