all MAX14912 outputs in push-pull and parallel mode switch @duty=30% while INPUT is always high.

Hi Davide,

This behavior is unusual. Could you please specify what you are using to create a 3.3mA load current, and what the current of the 24V supply is? Also, is the 24V supply stable?

Hi YuriyK1,

Thank you very much for your kindly reply.

My circuit is composed by 2 indipendent MAX14912 devices. They work both in push-pull and parallel mode, too.

The 24V is always stable becuse the load is almost negligable.

The supply circuit is made to bear 250mA x 16 outputs = 4A.  Please note that the 16 loads combined with the outputs (one for each output) are made up of a series of a LED and a 6.8Kohm resistor. They serve only to verify the physical value (0V...24V) of each output.

I think something intervenes, like a watch-dog or another protection that I inadvertently triggered through the circuit I made. The 30% percentage is really "strange".

Please note nor UVLO* and FAULT* open collector outputs intervenue.

Regards, Davide.

Hi Davide,

II cannot replicate the issue with the MAX14912 EV kit.
Is the 5V also stable? Could you please take an oscilloscope screenshot of the 5V input and OUT1?

Thanks, Yuriy

Hi YuriyK1,

I will expose my screenshots in few hours. This morning I must go out of the office to our customer. This afternoon I will reply to you with all voltages characterization..

Thank you very much for your support!.

Regards, Davide.

Hi YuriyK1,

Below two pictures. The first one is captured when IN1 [pin #27] is fixed at 3V3 voltage.

In the second one, the same pins are captured when IN1 is fixed at 0V. Again, IN1 (due to oscilloscope's maximumum traces reached) is not reported.

Please, look the scale of OUT1 is 500mV/div.

I wait your considerations. 

Thank you very much for your availability.

Regards, Davide.

Hi Davide,
All supplies appear to be in order. Could you check the SPI activity to ensure that CSN1_8 remains high?

Regards,
Yuriy

Dear Yuriy,

Thank for your reply. I made two checks. First of all I checked CSN1_8 was high during INx=1, but OUTx switch between 0V and 24V as descripted in my past pictures. The second one, I changed my card in order to made CSN1_8 always to "1" (= 3,3V physically), even during the power up of the supplies.

....But nothing changes.  Vout is always switching between 0V and 24V with a period of 10,45msec and ON-time of about 2,4msec despite VIN=VL=3,3V costantly.

Regards, Davide.

Hi Davide,

All power and SPI signals are confirmed to be good. The OUTx would only shut down automatically if there is overheating caused by an output current that exceeds the current limits. Please ensure there are no shorts to ground. We could try applying hot air (around 100°C) to the chip to see if the turn-on and turn-off timing is affected. Currently, at room temperature, the duty cycle is approximately 30%. It is anticipated that the duty cycle will decrease in a hotter ambient environment.

Regards,

Yuriy

Dear Yuriy,

Thanks for the explanation. Now I'm starting to explain the behavior I observed a little better..... It seemed to me that the 30% duty was not a coincidence!

In our circuit we have 16 independent and non-parallelized outputs, using - as I said - 2 MAX14912 devices independently and in parallel mode driven.

All outputs behave the same way I showed in the oscilloscope recordings, testing them individually.
We created two samples and the behavior between the 32 releases is the same. I measured once again and there are no short-circuits to GND or other voltages. As a test, the outputs are enabled one at a time.
We have created the outputs each with two external protection diodes (appropriately oriented, as per the above picture). Can they cause problems? The 24V voltage is external to the circuit.
P.S. I just received the MAX14912PMB#, the only development board for MAX14912 readily available (I should receive the MAX14912EVKIT# in a week). I'll try to modify it to make it work with SRIAL =0, ...but it doesn't seem that easy.

Thanks for collaboration.
Greetings, Davide.

Dear Yuriy,

I verified the ES1J diodes do not change the behaviour of the system.

Regards, Davide.