MAX13451E FAULT signal behavior

Hello,

Tying the A or B signals to GND will not assert the FAULT pin; it needs to be below GND to trigger. 

I will need to look more into why the shorted signals did not assert the FAULT pin. What is the driver output current when A and B are shorted together?

Hello,

The short-circuit current between A and B is ~53 mA.

Hello,

I have confirmed that since the FAULT pin is a push-pull driver, an external pull-down resistor is not required. With the resistor connected, what are you measuring at VL? Does the VL supply have enough current capability to source the pull-down resistor?

Hello,

We now tested the MAX13451E off-circuit (on a breadboard) and we see the same behavior: the FAULT only goes up to ~200 mV with a short-circuit on the A+B signals.
With the VCC=5V we tested with three different VL voltages (1V8, 3V3, 5V), but we basically see no current consumption on the VL pin (with and without the 100 kOhm pull-down resistor on the FAULT pin).
As I wrote in my first post the FAULT definitely changes if we add the short-circuit, but it only goes from ~60 mV to ~200 mV. It only goes close to the VL voltage if we add an over-voltage condition to the A/B signals.

Hello,

Some questions:

• Is the current in your supply being limited?
• Have you tested a different IC to rule out the possibility that the part has been damaged?
• Were you able to assert the FAULT pin by forcing A or B below GND while DE is high? At this point, is the short-circuit test the only one that is not asserting the FAULT pin?

Since the FAULT works as expected for an over-voltage condition, it could indicate that something in your application is preventing an overcurrent condition.

Hello,

I'm sorry for my late reply.

• I can confirm that we have nothing in our test setup that could limit the short-circuit current between the A and the B signals at that low level (~53 mA). The MAX13451E simply doesn't output more.
  I can see in the datasheet that two different short-circuit currents are specified:
  • Driver Short-Circuit Output Current: max. 280 mA
  • Driver Short-Circuit Foldback Output Current: min. 15 mA
    • Can this "Foldback current" explain the lower current we measure?
    • What is the minimum current level that should set the FAULT output HIGH?
• We tested multiple devices in and off circuit.
• Yes, I can confirm that the FAULT output goes HIGH if we apply an external voltage to the A or to the B signal that is higher than the VCC or lower than the GND.

Hello,

Apologies for the delay. It is odd that FAULT does not get asserted for the short circuit condition, but does for the under- and overvoltage conditions.

It does not seem like the current levels rose high enough to trigger the foldback circuitry, but I am unsure what current level would set the FAULT output high. I have reached out to the team more closely involved with this part and will get back to you once I receive a response. For now, I have some other questions:

• Can you clarify what you meant by testing multiple devices "in and off circuit"? Was the "off circuit" test a standalone IC, or was it still connected to other components?
• Is there anything connected to your FAULT pin, like an LED or microcontroller input?

Hello,

Thanks for checking the trigger level for the current limit in advance.

• Yes, during the "off circuit" testing we soldered a brand new IC on a TSSOP-DIP breakout and we did the measurements on a breadboard. We only had a multimeter connected to the FAULT pin in this setup.
• On our PCB ("in circuit") the FAULT signal is connected to an input pin of a GPIO expander.

Hello,

Unfortunately I was not able to get a specific answer from the team, so I will have to dig around in some older documentation to see if I can find anything.

I have also ordered the part myself to see if I am able to replicate the issue you are seeing. Please give me some time for the parts to arrive and for the testing. 

I know you mentioned testing multiple ICs already, so would you be able to send over photos of the top marks? I'd like to verify the ICs that you have.

Thanks.

Hello,

We have 5 identical parts on our PCB and all of them behave the same as described above:

This is one of the parts that we later tested on a breadboard and also behaves the same:

Thanks for your help in advance.