DRV8908-Q1: Negatie-current OLD and synchronous rectification mode

Shawn_Wang

Part Number: DRV8908-Q1

Hi team

I am confused on the negative-current OLD and synchronous rectification mode, could you help answer the following questions?

What is purpose of synchronous rectification mode? And when to enable this mode?
What is the status the motor is at for such a PWM waveform? OUT1_HS is always high but OUT2_LS/OUT2_HS is complementary?

over 3 years ago

0 Shinya Morita over 3 years ago

TI__Mastermind 44315 points

Hi,

Thank you for your questions.

1. Synchronous rectification is used to reduce power loss by diode recirculation. Please refer datasheet 8.3.1.1.2.2.

2. Figure 61 is case for this timing chart. OUT1_HS is continuous ON and OUT2 is under PWM operation.

regards

Shinya Morita

0 Shawn_Wang over 3 years ago in reply to Shinya Morita

TI__Expert 3811 points

Hi Shinya

Thanks for your reply.

Shinya Morita said:
Figure 61 is case for this timing chart. OUT1_HS is continuous ON and OUT2 is under PWM operation.

So why OUT1_HS is continuous ON and OUT2 is under PWM operation? Is this a normal working model? What is the status of motor under this condition?

0 Shinya Morita over 3 years ago in reply to Shawn_Wang

TI__Mastermind 44315 points

Hi,

Yes, it is common way to drive motor. When we want to change direction of motor spinning, OUT2_HS is continuous ON and OUT1 will is under PWM operation.

regards

Shinya Morita

0 Shawn_Wang over 3 years ago in reply to Shinya Morita

TI__Expert 3811 points

Hi Shinya

Shinya Morita said:
When we want to change direction of motor spinning

When talk to change direction, my understanding is the the current direction would also invert, so why "OUT1_HS is continuous ON and OUT2 is under PWM operation" could change direction of motor spinning? Is this just a middle status? I also noticed Synchronous Rectification is called Free-Wheeling Mode, how to understand it? Sorry for so many questions, I have DIN DRV8908-Q1 at a new project but I know little about this device.

0 Shinya Morita over 3 years ago in reply to Shawn_Wang

TI__Mastermind 44315 points

Hi Wang,

Probably these video may helps.

Driving a brushed DC motor - Bing video

Motor interfaces and PWM frequencies - YouTube

Thanks,

regards

Shinya Morita

Motor drivers

Motor drivers forum

DRV8908-Q1: Negatie-current OLD and synchronous rectification mode