LM7481-Q1: LM74810QDRRRQ1 how to reduce turn off time

Joe Miller1

Part Number: LM7481-Q1

Tool/software:

Dear Sir/Madam,
I am planning to use LM74810QDRRRQ1 to control a wiper motor.
The turn on time is fine (6ms) however the turn off time needs to be reduced (553ms).
To park the motor the turn off time needs to be under 200ms.
I have attached some scope shots from the EVM for turn on and off.
GREEN= EN/UVLO pin
YELLOW=VOUT
Motor current is 1.9A.

I was thinking about using a MOSFET load that is enabled when the LM74810QDRRRQ1 is disabled.
Not sure if this has been done on any TI EVMs.
Suggestions are welcome.

Regards Joe

3 months ago

0 Shiven Dhir 3 months ago

TI__Mastermind 21160 points

Hi Joe,

By turn-off, we can provide a solution that can cut-off the path instantly. Once EN is low, HGATE goes low quiet instantly (<1ms) and the path is cutoff. After that depending on the load and output capacitor, VOUT will take its time to discharge, and controller can't help in that. If you want QOD (quick output discharge), you may have to add external circuit.

Regards,

Shiven Dhir

0 Joe Miller1 3 months ago in reply to Shiven Dhir

Intellectual 325 points

Dear Shiven Dhir,
Thank you for the reply.
Yes, I am after QOD (quick output discharge).
Output load capacitance is 47uF.
Lower capacitance results in longer startup (repeated triangular then start) and very high inductive spikes.
Do you have any recommendation for external circuit that is small.
Regards Joe

+1 Shiven Dhir 3 months ago in reply to Joe Miller1

TI__Mastermind 21160 points

Hi Joe,

You can simply add a QOD circuit like this controlled by EN. If current is high enough, you can add limiting resistor as well.

Regards,

Shiven Dhir

0 Joe Miller1 3 months ago in reply to Shiven Dhir

Intellectual 325 points

Dear Shiven Dhir,
Thank you for the reply.
I will prototype up the circuit below and add to the LM74810 EVM.
Component values are just place holders for discussion.

Regards Joe

0 Shiven Dhir 3 months ago in reply to Joe Miller1

TI__Mastermind 21160 points

Hi Joe,

Looks good.

Regards,

Shiven Dhir

0 Joe Miller1 3 months ago in reply to Shiven Dhir

Intellectual 325 points

Dear Shiven Dhir,

Thank you.

Regards Joe

0 Joe Miller1 3 months ago in reply to Joe Miller1

Intellectual 325 points

Hi,
Just wanted to post an update.
Parts on hand were SI7113DN-T1-GE3 (P-MOS) and SIR820DP-T1-GE3 (N-MOS).
There was very little impact 1K to 100R.

2x10R

2x5mR

Regards Joe

0 Shiven Dhir 3 months ago in reply to Joe Miller1

TI__Mastermind 21160 points

Hi Joe,

Looks like QOD is working fine.

Although I see that VDS of the chosen QOD FET is only 20V. I hope you have taken that into consideration.

Regards,

Shiven Dhir

0 Joe Miller1 3 months ago in reply to Shiven Dhir

Intellectual 325 points

Dear Shiven Dhir,
The SIR820DP-T1-GE3 (N-MOS) VDS is 30V. It is the only part I have on hand for testing.
Same issue for resistors.
I plan to use NVMYS6D2N06CLTWG (N-MOS). Same part I currently use for LM74810 with VDS of 60V.
I just need to calculate the resistor size and dissipation.
Regards Joe

0 Shiven Dhir 3 months ago in reply to Joe Miller1

TI__Mastermind 21160 points

Hi Joe,

Apologies, I checked the incorrect FET.

Regards,

Shiven Dhir

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LM7481-Q1: LM74810QDRRRQ1 how to reduce turn off time