DRV8718-Q1: Low side application

Hi,

Thank you for your questions. I will review it and feedback to you by next Tuesday.

regards

Shinya Morita

Shinya,

If I left SHx open, should I set any register to avoid any warning?

Thanks

Hi Ryan,

Not really. However off course should not enable the high side.

regards

Shinya Morita 

Hi Ryan,

Ryan Wang said:

SHx pin is only used to sense voltage of high side MOSFET sourcing pin, right?

SHx pin is also used to monitor the VDS for open and short circuit for devices with SPI bus. In this case, you need to disable the feature by programming the register EN_OLSC bit setting.

From datasheet:

8.3.8.12 Offline Short Circuit and Open Load Detection (OOL and OSC)

The device provides the necessary hardware to conduct offline short circuit and open load diagnostics of the external power MOSFETs and load. This is accomplished by an integrated pull up and pull down current source on the SHx pin which connect to the external half-bridge switch-node. The offline diagnostics are controlled by the associated registers bits in the OLSC_CTRL register. First, the offline diagnostic mode needs to be enabled through the EN_OLSC register setting. Then the individual current sources can be enabled through the PD_SHx and PU_SHx register settings. The voltage on the SHx pin will be continuously monitored through the internal VDS comparators. During the diagnostic state the VDS comparators will report the real-time voltage feedback on the SHx pin node in the SPI registers in the associated VDS register status bit. When in the VDS comparators are in diagnostic mode, the global DS_GS SPI register bits will not report faults or warnings. Before enabling the offline diagnostics it is recommended to place the external MOSFET half-bridges in the disabled state through the EN_DRV register setting. Additionally, the VDS comparator threshold (VDS_LVL) should be adjusted to 1-V or greater to ensure enough headroom for the internal blocking diode forward voltage drop.

On H/W device variants, this feature is not available.

Brian

Brian, Shinya,

Let me double confirm:

"SHx pin is also used to monitor the VDS for open and short circuit for devices"

This mean monitor VDS for high side MOSFET, right?

Now customer want to use DRV8718 for 6 half bridge control. But there is only one high side MOSFET connect with GH1 , SH1 which is shared by all 6 channel LSD.

All 6 Low side MOSFET drain connect with high side MOSFET source& SH1.

For this case, no need to worry about EN_OLSC or any other monitor, right?

Hi Ryan,

Ryan Wang said:

This mean monitor VDS for high side MOSFET, right?

When enable, this feature (EN_OLSC)  monitors both high side and low side FETs, not just high side.

Ryan Wang said:

Now customer want to use DRV8718 for 6 half bridge control. But there is only one high side MOSFET connect with GH1 , SH1 which is shared by all 6 channel LSD.

All 6 Low side MOSFET drain connect with high side MOSFET source& SH1.

For this case, no need to worry about EN_OLSC or any other monitor, right?

If you want to use low side control for the 6 loads, then why even use a high side FET connected to VGHx? The loads can all be connected to VM or power supply. According to your first post, I don't see the need to have an upper FET connected.

Brian

Hi Team,

The purpose of still adding one high side FET, is because they worried about if anything happened on the low side FET, make it unable to be turned off, they still can turn off the high side FET. 

Means high side FET turned on, and low side FET output the PWM. 

The schematic is under here, will it work?

I agree with Shinya that each inductive load should have a Schottky diode in parallel.

Brian