Brake mode during Sleep mode

Shunsuke Nagata

Other Parts Discussed in Thread: DRV10970

Hi,

Could you please let me know below questions for DRV10970?

1. PWM duty:
I would like to know the relation between PWM duty cycle and Output current. e.g. When PWM is 0%, Output current is 0A. And When PWM is 100%, Output current is 1.5A(Peak output current). It may has Linearity. Is it correct?

2. Could you please confirm the state in ramping down for Sleep mode? As datasheet shows below, the motor state will be brake mode or coast mode. When BRKMOD = 1, will the state be BRAKE mode?

Regards,
Nagata.

over 4 years ago

0 Vishnu Balaraj over 4 years ago

TI__Mastermind 24415 points

Hi Nagata-san,

Thanks for posting your question in MD forum. See my response below:

1. PWM duty cycle and output current (phase current) does not have a linear relationship. This is because the applied voltage to the motor is the sum of voltage drop across stator resistor, voltage drop across stator inductor and the BEMF voltage. Inductive effect of the motor makes the relationship between duty cycle and phase current non-linear. Below is the voltage equation of the motor:

Vm = iR+ L(di/dt) + Vbemf.

2. Motor state when ramping down to sleep mode depends on how the BRKMOD pin is configured. If the pin is pulled Low the device is configured to Coasting mode. If pulled High, the device is configured to Brake mode.

Regards,

Vishnu.

0 Shunsuke Nagata over 4 years ago in reply to Vishnu Balaraj

TI__Genius 13060 points

Vishnu.

For #1, please separate motor voltage and output current and could you please let me know the relation between PWM duty and output current? I understand motor voltage is depend on stator inductor and BEMF voltage.

I guess the Internal controller will set output current based on PWM duty. Then the controller theoretically set output current linear with PWM inputl?

Regards,
Nagata.

0 Vishnu Balaraj over 4 years ago in reply to Shunsuke Nagata

TI__Mastermind 24415 points

Hi Nagata-san,

Output voltage = PWM duty cycle * Supply Voltage.

When PWM duty cycle increases, output current will also increase non-linearly. The device will only apply voltage across the motor terminals and it will not set the output current. Phase current/Output current depends on the load of the motor. The device will have control only on the phase voltages.

Regards,

Vishnu.

0 Vishnu Balaraj over 4 years ago in reply to Vishnu Balaraj

TI__Mastermind 24415 points

Please note that output voltage means phase voltage.

0 Shunsuke Nagata over 4 years ago in reply to Vishnu Balaraj

TI__Genius 13060 points

Vishnu,

What is the resolution for PWM duty? For example, Can user set PWM duty by 0.1% (Can he set 20.1%, 20.2%,etc?) or should he set 20%, 21%,,?

Regards,
Nagata.

0 Vishnu Balaraj over 4 years ago in reply to Shunsuke Nagata

TI__Mastermind 24415 points

Hi Nagata-san,

The resolution for PWM duty cycle is 0.2%.

Regards,

Vishnu

0 Shunsuke Nagata over 4 years ago in reply to Vishnu Balaraj

TI__Genius 13060 points

Vishnu,

Thank you very much for your support.

Could you please give support for BRAKE?

As my customer check the brake feature of DRV10970, it looks like different work between normal and wait for motor to stop before sleep.

Normal : Brake using with reverse current.
Before sleep : Short brake

Is it correct?

Regards,
Nagata.

0 Vishnu Balaraj over 4 years ago in reply to Shunsuke Nagata

TI__Mastermind 24415 points

Hi Nagata,

Your question is not clear to me. DO you mean to say that the motor is not braking even after configuring BRKMOD pin to 1?

Regards,

Vishnu.

0 Shunsuke Nagata over 4 years ago in reply to Vishnu Balaraj

TI__Genius 13060 points

Vishnu,

I believe there are two method for the brake as common. One is short brake and another is revers current.

Which idea is using in the status of ramping down to sleep mode?

Regards,
Nagata.

0 Vishnu Balaraj over 4 years ago in reply to Shunsuke Nagata

TI__Mastermind 24415 points

Hi Nagata,

I don't know the definition of both brake methods you mentioned but in DRV10970, when BRKMOD pin is pulled HIGH, all the low side FETs are turned ON. This type of braking is commonly known as "Passive" braking. Hope this answers your question.

Regards,

Vishnu.

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Brake mode during Sleep mode