about DRV8824-Q1's FAULT function and UVLO function

Hi Yamamoto-san,

I would like to know the function of FAULT and UVLO.

1. Please teach me the motion of motor when the FAULT is active.

I think that the motor rotates to the original position under FAULT function.

But I don't know the speed.

Does the motor rotate to the original position quickly? or slowly?

There are a few variables that can affect this, such as speed of the motor when the event occurs. Once re-enabled, the DRV8824 will attempt to drive the motor to the nearest home state. This will be quick and the motor may move 1 or 2 full steps in either direction. This actual movement will depend on the number of degrees/full step.

When FAULT is active, the DRV8824 outputs are disabled. This can be due to Overcurrent or Overtemperature. If overcurrent, the DRV8824 must be reset by cycling nRESET or VM. If overtemperature, the DRV8824 will begin running once the temperature has decreased.

2. Please teach me the reason why UVLO is set to 7.8V.

My customer want this device not to be inactive around 6V to deal with cold cranking.

Please teach me the way to be inactive UVLO if there is the way.

Or, I would like to know the reason why UVLO is set to 7.8V.

Unfortunately, UVLO was set based on the DRV8824. The DRV8824-Q1 spec matches it. The only method to prevent the device from becoming inactive is to keep VM above the UVLO voltage.

Dear Rick,

Thank you for your reply.

Additionally, I would like to know more.

3. about UVLO

Does the DRV8824 drive the motor to the home state in UVLO?

If this drive to the home state, when does this drive? (at falling below the UVLO? or at operation resuming?)

Datasheet says 'Operation will resume when VM rises above the UVLO threshhold' in page.16.

This operates automatically?

Additionally, 

3-1.  If nENBL is low during VM terminals falling below UVLO and rising UVLO, can DRV8824 drive to the home state?

3-2.  Why does the UVLO be set at 7.8V?

4. about nENABLE and nRESET

I would like to know the difference between nENABLE and nRESET.

Are there differences to use these as the situation demands? 

5.about sequence control

Is there document about DRV8824's sequence control?

6.. about quiescent current

My customer considers turning off this device by 'nENBL-high & nRESET-high' or 'nENBL-high & nRESET-low'.

How much does quiescent current flow at each situation?

Best regard,

Hi Yamamoto-san,

Takao Yamamoto said:

Additionally, I would like to know more.

3. about UVLO

Does the DRV8824 drive the motor to the home state in UVLO?

If this drive to the home state, when does this drive? (at falling below the UVLO? or at operation resuming?)

Datasheet says 'Operation will resume when VM rises above the UVLO threshhold' in page.16.

This operates automatically?

Answer: When the DRV8824 enters UVLO, the motor outputs are not driven. The outputs are disabled and the internal logic is reset. When VM rises above UVLO threshold, the DRV8824 begins driving the motor outputs again. The DRV8824 will begin driving at the home state. This is highlighted in Table 2 of the datasheet.

Takao Yamamoto said:

Additionally, 

3-1.  If nENBL is low during VM terminals falling below UVLO and rising UVLO, can DRV8824 drive to the home state?

Answer: When nENBL is low during VM falling below and rising above UVLO, DRV8824 will stop driving the motor outputs when VM falls.  DRV8824 will begin driving the motor outputs at the home state when VM rises. 

Takao Yamamoto said:

3-2.  Why does the UVLO be set at 7.8V?

Answer: We will do a little research on this and get back to you.

Takao Yamamoto said:

4. about nENABLE and nRESET

I would like to know the difference between nENABLE and nRESET.

Are there differences to use these as the situation demands? 

Answer: nRESET can be used to reset the DRV8824 in an OCP condition. nRESET can also be used to reset the index table to the home state.

nENBL is used to turn the DRV8824 outputs on and off. nENBL has no effect on the index table. This is typically done when in cases where the application spins the motor, but does not require holding torque.

Takao Yamamoto said:

5.about sequence control

Is there document about DRV8824's sequence control?

Answer: Can you clarify this question?

Are you asking for power up sequence, the sequence of currents steps during operation, or something else?

Takao Yamamoto said:

6.. about quiescent current

My customer considers turning off this device by 'nENBL-high & nRESET-high' or 'nENBL-high & nRESET-low'.

How much does quiescent current flow at each situation?

Answer: Both conditions should be approximately the same at 5 mA typical at 24V. If looking for lowest quiescent current, set nSLEEP low. This will reduce the current to less 10uA typical at 24V.

Dear Rick,

Thank you for your gracious answer.

Additionally, I would like to know more.

7. about your answer 1

7-1.

You said 'This will be quick and the motor may move 1 or 2 full steps in either direction.'

What is the mean of '1 or 2 steps' ? I think that the motor move 1 full step in either direction because of supplying current 71% to each wires.

7-2.

You said 'If overtemperature, the DRV8824 will begin running once the temperature has decreased.'

I can't understand the mechanism of re-running.

Will the DRV8824 begin driving at the home position once the temperature has decreased?

Is the motor going to rotate from the home position? or from the motor stopped?

8. about your answer 3-2

Has this been cleared?

9. about my question 5

9-1. What is the definition of 'Home Position'?

I would like to know all conditions that DRV8824 begin driving at the home position.

By the way, does DRV8824 begin driving at the home position after nENBLE or nSLEEP operation?

9-2. If the following protocol I think, please fix a mistake.

I think that the following when the motor re-rotate from home position.

********************************************************************************************

something wrong happen→something protection active→outputs inactive→

→something wrong cleared→internal logic reset→internal regulator active→supply current to home position→

→rising edge of STEP can be recognized→motor rotate

********************************************************************************************

10. about difference of nENBLE and nRESET

I would like to know the difference between nENABLE and nRESET.

Are there differences to use these as the situation demands? 

Best regards,

Dear Rick,

Sorry to trouble you, but I need your help as soon as possible.

Could you work on what you can answer first?

Best regards.

Hi Yamamoto-san,

Takao Yamamoto said:

7-1.

You said 'This will be quick and the motor may move 1 or 2 full steps in either direction.'

What is the mean of '1 or 2 steps' ? I think that the motor move 1 full step in either direction because of supplying current 71% to each wires.

A stepper motor has 4 possible full step polarities/alignments (you can see these in the step table). They are +71/+71, -71/+71, -71/-71, and +71/-71. The cycle then repeats. This means the rotor of the stepper motor is a most 1 or 2 steps from a +71/+71 position.

Takao Yamamoto said:

7.2

You said 'If overtemperature, the DRV8824 will begin running once the temperature has decreased.'

I can't understand the mechanism of re-running.

Will the DRV8824 begin driving at the home position once the temperature has decreased?

Is the motor going to rotate from the home position? or from the motor stopped?

I am double checking on this and will get back to you. The indexer does not reset when the device enters thermal shutdown. Once thermal shutdown has been cleared the device will resume operatetion from the current point in the indexer table.

Takao Yamamoto said:

8. about your answer 3-2

Has this been cleared?

Unfortunately this is a limit of the device. It was not designed to support low voltage (<8V) cold crank operation.

Takao Yamamoto said:

9-1. What is the definition of 'Home Position'?

I would like to know all conditions that DRV8824 begin driving at the home position.

By the way, does DRV8824 begin driving at the home position after nENBLE or nSLEEP operation?

The possible conditions that can reset the indexer to the home position are: nSLEEP, nRESET, UVLO.

It will not reset to the home position after nENBL. It will reset to the home position after coming out of SLEEP mode.

Takao Yamamoto said:

9-2. If the following protocol I think, please fix a mistake.

I think that the following when the motor re-rotate from home position.

********************************************************************************************

something wrong happen→something protection active→outputs inactive→

→something wrong cleared→internal logic reset→internal regulator active→supply current to home position→

→rising edge of STEP can be recognized→motor rotate

********************************************************************************************

Your understanding appears to be correct.

Takao Yamamoto said:

10. about difference of nENBLE and nRESET

I would like to know the difference between nENABLE and nRESET.

Are there differences to use these as the situation demands? 

nENBL will disable the outputs (Hi-Z) but keep the position of the indexer. It will not clear an OCP FAULT. nRESET will disable the outputs (Hi-Z), clear any FAULTs, reset the logic, and reset the indexer to the home position.