DRV11873: Inquiries about DRV11873's FG side output failure

Grady Lee said:

Q1) If you look at the Electrical Characteristics of the datasheet, the current for driving is FG pin sink current: Min 5mA.

If you use it with a current lower than Min 5mA, what problems are expected? (Please answer with technical content.)

1. The datasheet say 5mA is the min current when tested at 0.3V at FG pin, so if the test condition with lower than 0.3v at FG pin then the sink current can be lower than 5mA. IOW, 5mA is not the minimum sink current, but it is characterized only with 0.3v at FG.

The FG can work with sinking current less than 5mA, depends on the voltage at FG pin. Say if FG is pulled up to 5v with 100K resistor, then the sinking current will around 5v/100K = 50uA.

Grady Lee said:

However, when analyzing the FG-side defective output sample, the FG waveform is output, but it is output at a low voltage level (7V to 10V) instead of 12V, and there are also defective samples in which the FG pulse is not

output.

I am using the FG side current as 11mA. What could be the cause of the output voltage drop as above?

With a damaged part, there is the the FG internal open drain FET can be damaged and so even when it is turned off (open drain) its current is not zero and so the reason for the voltage drop.

Brian

Hi Grady,

I will get back to you on Tuesday.

Regards,

Vishnu

Hi, Brian

Thank you for reply.

There are additional inquiries from the customer regarding the answer.

[Brian Dang said-1]

The datasheet say 5mA is the min current when tested at 0.3V at FG pin, so if the test condition with lower than 0.3v at FG pin then the sink current can be lower than 5mA. IOW, 5mA is not the minimum sink current, but it is characterized only with 0.3v at FG.

The FG can work with sinking current less than 5mA, depends on the voltage at FG pin. Say if FG is pulled up to 5v with 100K resistor, then the sinking current will around 5v/100K = 50uA.

→ Q1) If it can operate with a sinking current of less than 5mA depending on the voltage, does that mean that 12V/100k = 0.12mA is okay?
            Is there any problem in operation if only about 5v/100K = 50uA flows?
            What is the minimum sink current based on 12V?

[Brian Dang said-2]

With a damaged part, there is the the FG internal open drain FET can be damaged and so even when it is turned off (open drain) its current is not zero and so the reason for the voltage drop.

→ Q2) In addition to the fact that the FET may be damaged and cause a voltage drop,
The customer inquires about the cause of damage to the FG stage FET even though it was used within the normal current range (within FG pin shot current limit Vfg=12V 25mA) based on the datasheet.
- If the problem occurs even after normal use on the datasheet, is there no defect in the DRV11873 itself?
- If it is difficult to answer a clear cause, please refer to the attached circuit diagram and defective product measurement data to answer even the probable cause.

Q3) Is there any way to improve the above defects? (technical or documentation, etc.)

Q4) When a fault occurs on the FG output side of the defective IC of the "5/18_Defective product" attached above, when the water purifier set program is modified so that the motor operates regardless of FG reception, is there any problem in using the motor?
If there is a problem, what kind of problem will occur? (Will there be any problem even if the FET is continuously used in a damaged state?)

Please check. Thank you.

Grady,

Apologies for the delay. I still get a chance to check your post. Will get back to you tomorrow.

Regards,

Vishnu 

Hi, Vishnu

I have not yet received a response to my inquiry.
Customers want a reply.

Please check. Thank you.

Grady,

See my response below.

Grady Lee said:

Q1) If you look at the Electrical Characteristics of the datasheet, the current for driving is FG pin sink current: Min 5mA.

If you use it with a current lower than Min 5mA, what problems are expected? (Please answer with technical content.)

FG sink current depends on the RdsON of the internal open drain FET. When the voltage on FG pin is 0.3V, and when the Open drain fet is turned ON, current drawn by the FG pin (sink current) from 0.3V can be min of 5 mA. 

Grady Lee said:

Q2) A pull-up resistor (100K) is applied to the motor FG side output line (12V).In the case of a non-defective sample, 12V level and normal pulse are normally output.

As Brian mentioned, this could be due to some leakage current in the FG pin. This means the device is damaged. This can happen if applied voltage on FG is greater than the abs max of FG pin as mentioned in the datasheet. 

Grady Lee said:

Q3) Is there a history of the same problems and defects as above in the past?

We haven't' seen such issues in the past!

Regards,

Vishnu

Hi, Vishnu.

The content of your answer is not an answer to additional inquiries after Brian's answer.

The additional inquiries made 3 days ago are as follows.

There are additional inquiries from the customer regarding the answer.

[Brian Dang said-1]

The datasheet say 5mA is the min current when tested at 0.3V at FG pin, so if the test condition with lower than 0.3v at FG pin then the sink current can be lower than 5mA. IOW, 5mA is not the minimum sink current, but it is characterized only with 0.3v at FG.

The FG can work with sinking current less than 5mA, depends on the voltage at FG pin. Say if FG is pulled up to 5v with 100K resistor, then the sinking current will around 5v/100K = 50uA.

→ Q1) If it can operate with a sinking current of less than 5mA depending on the voltage, does that mean that 12V/100k = 0.12mA is okay?
            Is there any problem in operation if only about 5v/100K = 50uA flows?
            What is the minimum sink current based on 12V?

[Brian Dang said-2]

With a damaged part, there is the the FG internal open drain FET can be damaged and so even when it is turned off (open drain) its current is not zero and so the reason for the voltage drop.

→ Q2) In addition to the fact that the FET may be damaged and cause a voltage drop,
The customer inquires about the cause of damage to the FG stage FET even though it was used within the normal current range (within FG pin shot current limit Vfg=12V 25mA) based on the datasheet.
- If the problem occurs even after normal use on the datasheet, is there no defect in the DRV11873 itself?
- If it is difficult to answer a clear cause, please refer to the attached circuit diagram and defective product measurement data to answer even the probable cause.

Q3) Is there any way to improve the above defects? (technical or documentation, etc.)

Q4) When a fault occurs on the FG output side of the defective IC of the "5/18_Defective product" attached above, when the water purifier set program is modified so that the motor operates regardless of FG reception, is there any problem in using the motor?
If there is a problem, what kind of problem will occur? (Will there be any problem even if the FET is continuously used in a damaged state?)

Please check. Thank you.

1) yes, 0.12ma is ok

2) The FG circuit could be damaged if the driver chip was damaged due to other issues such as output or supply acceded absolute specifications, even if the FG current was within the spec. IOW, when the chip is damaged anything can happen to FG behavior.

3) I don’t think the issue is about the FG circuit design. What if the issue is related to the MCU or other devices that reads the FG signal?

4) FG is a status out put and so I don’t think it can affect the motor operation if you want to continue the operation in the emergency, but I would not manufacture and sale the product knowing the FG circuit not working without knowing the cause.

Brian

Hi Grady,

I'm aligned with Brian's feedback. 

Regards,

Vishnu