TIOS1013: Does LDO have reverse current protection?

Hi Sinjon,

There is not reverse current protection on the VCC_OUT pin to prevent any current flowing into the LDO circuit while you are programming your board with an external source. 

Most of the TIOL1113 device is powered through the L+ supply pin and there is a forward blocking diode between the L+ and the LDO circuit.  Forcing a voltage on the VCC_OUT pin without L+ active will power the LDO circuitry which will consume no more than a few hundred uA's.  I do not have data on the exact leakage current, but it is in this range.  As long as the voltage applied is less than 5.5V, there should be no damage to the TIOL1113 device.

What voltage are you applying with the external programmer?

Is there a voltage output on the VCC_OUT pin following your programming when L+ is applied?  Or is this voltage either missing or at a different voltage than was output prior to the programming?

Regards,
Jonathan

Thanks for the help Jonathan,

I took a look at the most recent board that has stopped working for me. 

When connecting 24V to VCC(I'm using a TIOS1013 not the TIOL113) I am getting 3.4V on the VCC_OUT pin.

When I apply 3.3V with the external programmer I seem to also get 3.3V throughout the node. So it looks like the LDO isn't damaged. 

Here's some more information about the circuit: 

The VCC_OUT LDO is being used to power an LDC1612 with an external 40Mhz TCXO, and an ATMega328P with an external 8Mhz crystal.

I have a 10kΩ pull up for the RESET on the ATMega328P. 

I did notice that the 8Mhz crystal is not oscillating anymore which is the most likely reason I can no longer program via ISP.

Seems to me that the hardware all functions as intended minus the crystal.

So my best guess is there must be some sort of transient or behavior caused by either the LDO or the LDC1612 that causes RESET to toggle while the chip is being erased and written so the fuses are not correct. That's the only thing I can think of why the crystal is not oscillating anymore.

Any thoughts on this?

I'm sorry for using the TIOL1113 part number in my response instead of the TIOS1013.  They are very similar devices and the answer remains the same for both devices.

I really only have expertise with the TIOS1013 device in this system.  I did read through the LDC1612 datasheet and the ATMega328P datasheets but I didn't see anything obvious for a root cause.

Have you monitored 3.3V power and Reset signals, and perhaps any other nets that may be sensitive to the programming when you are trying to program the MCU?  If so, have you observed any transients?

Also, have you tried to remove either the TIOS1013 or LDC1612 device on a board that you are having programming difficulty?  Potentially removing one or both devices would help narrow down the source of the problem.

Regards,

Jonathan

I'll try removing the TIOS1013 and LDC1612 one at a time to see if I can find out which is causing my problem! With my luck it will probably be neither ha

Thanks for your help, I'll let you know what I find out.