I have a board with a DRV8830 i2c motor driver that runs at 6V. The board's CPU runs at 3.3V.
The 6V power is provided by an LDO that can be shutdown by the CPU to lower power consumption.
But when 6V is gone from the DRV8830, and i2c SDA/SCL are HIGH (idle/sleeping) there's a current leaking through the DRV8830 of about 300uA.

Is it possible to put a mosfet between the data lines that will only conduct when 6V power is enabled? Or is it a bad idea to put a mosfet between i2c datalines?

I'm not sure how to do this correctly. I'm open to suggestions.

 

I haven't worked with them personally, but there are ICs that are similar to relays in how they operate. I believe they are normally called switches. I can't look up any info at the moment, but will get some part numbers when I get a chance if anyone doesn't offer a better solution by then.

 

The I2C inputs to the DRV8830 have a maximum high threshold of 3.0V (50% Vcc), so just connect the pull-ups to the 3.3V supply.

 

My i2c lines are pulled up to 3.3v. No pullup to 6v. But still there’s a current flowing of about 300uA when +6V is shut down.
The current goes away if I disconnect the sda ald scl lines. Or when removing GND from the drv8830 chip.

 

What voltage do you measure on the DRV’s power supply pin?
if it is slightly above 0V when it has no power supply then the current is going through its protection diodes into its power supply.
Why do you need to disconnect its power supply?

 

I need to turn off the drv8830 mainly because the LDO will consume 50uA when it’s active and only 2uA when the LDO is shutdown.
It’s a battery operated device.

I’ll measure the power voltage as soon as i’m back in my office. Over 1-2 hours.

 

but I did test removing power from the drv8830. Leaving the pin floating. And still current was flowing. It went away after disconnecting GND from the drv8830 or by disconnecting both SCL and SDA

 

You should be able to to put a small N-MOSFET in series with the SDA/SCL lines (source towards the DRV8830 and gate to 6V) to prevent the leakage.
The MOSFET would need to be a logic-level type with a maximum Vgs(th) of ≤1.5V.

 

Why do you need an LDO when the DRV8830 can regulate the motor voltage using PWM?
That would reduce the losses and improve battery life.
the DRV8830 can shut down to 300nA.

 

The drv8830 max voltage is 6.7v. The device runs of a 2 cell pack, max 8.4v. So, that’s why I added an LDO.

 

Why can’t you just tristate the SCK and SDA lines, i.e. make the inputs?

 

Why can’t you just tristate the SCK and SDA lines, i.e. make the inputs?

Because the pull-up resistors are permanently connected. Current flows from the 3.3V supply, through the pull-ups, through the DRV protection diodes into the (disabled) 6V supply.

 

Because the pull-up resistors are permanently connected. Current flows from the 3.3V supply, through the pull-ups, through the DRV protection diodes into the (disabled) 6V supply.

Oh, OK. If there is no other use of the SPI interface, you could set them low when the driver chip is disabled.

edited: Never mind, that would also cause the leakage.

 

It’s unfortunate that there isn't a higher voltage version, because dropping a couple of volts with a linear regulator isn't going to be efficient. I use Toshiba's TB67H450. It's not IIC but it still only take two wires to interface it, but it does require a PWM output from the processor.

 

Oh, OK. If there is no other use of the SPI interface, you could set them low when the driver chip is disabled.

edited: Never mind, that would also cause the leakage.

If it were SPI not IIC, with no pullups, then it would be OK.

 

I added two BSS138 mosfets on the SDA/SCL lines like suggested in here. It works perfect!

 

I added two BSS138 mosfets on the SDA/SCL lines like suggested in here. It works perfect!

If there is anything else on the IIC bus which is required when the DRV is off, then it won't work.
If the IIC bus only drives the DRV, then it will be fine.

 

I added two BSS138 mosfets on the SDA/SCL lines like suggested in here. It works perfect!

Glad to hear it worked.

 

Wouldn't supplying the pullup voltage from a port pin do the job? Make the port pin high when using I2C, low otherwise.

 

If there is anything else on the IIC bus which is required when the DRV is off, then it won't work.
If the IIC bus only drives the DRV, then it will be fine.

The mosfets are on the drv8830 side. Other i2c devices are connected directly to the i2c bus. The mosfets will only disconnect the sda/scl lines to the drv8830.

It shouldn’t impact the other i2c devices?