AMC6821: using part without an external FET

Tim,

Let me look into it and get back to you this afternoon.

-Kelvin

Tim,

Could you share your schematic?

The max input (sink) current is 10mA according to the Abs Max Rating and the max input voltage is 6.5V.

In the EVM schematic, it shows that AMC6821 can drive a PWM pin directly for a 4-wire fan.

www.ti.com/.../slau195a.pdf


-Kelvin

Hi Kelvin-

What would happen if pins 9 and 10 are left floating – would there be “latch-up” or whatever it is that we are maybe
seeing? If so, would simply shorting the 2 pins together eliminate the possibility? Is there a recommended way of
tying off these unused inputs?

I'd rather not post the schematics. Can I send them to you directly through email?

Thanks for your help,

-Tim

Tim,

Shorting the remote pins (IN+ and IN-) together should give  consistent temperature result of -128°C.

-Kelvin

TI fan controller.docxHi Kelvin-

That was not the question. The question is, could leaving these pins float (because we are using the internal temp senor) cause the type of problems we are seeing (i.e., the IC heating way up). Or, what might cause the IC to heat up when the system is at room temperature. Note this problem only happens occasionally.

See attached for schematics.

Tim,

Which fan control mode are you using?

-Kelvin

Hi Kelvin-

We run in Software-DCY mode, using the internal temp sensor.

-Tim

Since you're using the Software-DCY, you don't need the remote inputs. I don't see why you can't floating these pins.
Are you able to reproduce the heating problem at will? I'm not sure why the IC would heat up occasionally unless there's some shorts...

-Kelvin

Tim,

Did you make progress with the bug?

-Kelvin

Hi Kelvin-

No we are not able to reproduce the problem at will. It happens sporadically. 

We wonder if any other customers use this device and see similar? Or leave pins 9 and 10 floating? Or any other suggestions you have for us?

Thank,

-Tim

Tim,

This is the first time that I haven't heard of a problem like this for SW mode.  Usually, we recommend the customer shorting pin 9 and pin 10 together.

I would recommend monitoring the supply current of amc6821. This might give you a clue during the event if the amc is pulling more current through the Vcc.

-Kelvin