LMZ315x0 / About INH pin

Hello,

I have another question about the INH pin: 

In the LMZ31520 data sheet page 4 note (3), it is recommended to use a very low-leakage transistor to drive the INH pin (I<300nA).

I don't found any MOSFET that fits this requirement.

What is the reason for a so low current value ?

Thank you very much

Hi Sneha,

I recently use two LMZ31520 on a board. The power rails generated must be sequenced.

To do so, I drive the first component INH pin by a general reset circuit through a BSS138 transisor.

The PWRGD output of the first LMZ is then directly wired to the INH pin of the second LMZ device.

I only use the internal pull-up of the first device (pin PWRGD_PU is wired to V5V).

It works very well.

Regards

Daniel

Hello Sneha,

The INH pin of the LMZ31530 is internally set by a resistor bridge between VIN (10KOhms pull-up) and GND (6.65KOhms Pull-down). See functional block diagram on page 8 of the LMZ31530 data sheet.

So, the hi-level of INH pin is dependent of VIN value.

For example, if VIN=12V, the INH level will be 4.79V and the internal current in the resistor bridge will be 0.721mA.

You can calculate the leakage current of your Linear Technology regulator by measuring the INH level with or without connecting the PGOOD output to the INH input.

I hope that your design will work fine.

For my information, what is your VIN level and what is the Linear Technology regulator you use ?

Regards

Daniel

Hi Daniel,

Thank  you very much  for the support.  It is very clearly explained.

Our input voltage is 19V and we use a micromodule from Linear technology.

regards,

Sneha

Hi Sneha,

Although absolute rating voltage is 20V max for VIN and PVIN pins, the recommended operating voltage is 14.5V max.

So , I'm affraid that 19V is a little bit too high if you planned to input this rail directly to your LMZ31530 device input.

Regards

Daniel

All right !

Good luck for your design.

I hope It will working well :-)

Daniel

Thank you very much.