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D24V6F5 Enable/Disable with PIC microcontroler

I have NanoPi DUO2 powered from 12V battery with D24V6F5 regulator. Because the device will be mostly unattended I need solid watchdog solution.

So I have designed separate circuit base on small PIC 12F1571. PIC on pin RA2 receive “heart beat” signal from NanoPi and in case when hard reset is necessary send “0” on pin RA4 - connected to SHDN pin on D24V6F5. But nothing happens - D24V6F5 don’t react on changing voltage level on pin SHDN from 5V to 0V.

To be sure that shutdown signal is delivered I have soldered led with 1k resistor between GND and SHDN to see what happens because touching SHDN pin with multimeter reset D24V6F5 module.

Please look at schematic attached.

What I’m doing wrong ? I have tested this on two D24V6F5 modules.

regards
Slawek

Hi, Slawek.

The schematic does not show how the +5V from the regulator connects to the rest of your system, could you post a schematic or diagram of the full circuit? Did you ever test the shutdown of the regulator before soldering it to board?

“touching SHDN pin with multimeter reset D24V6F5 module”

This makes me suspicious of a weak connection somewhere or a missing ground connection.

-Claire

Hi Claire,

thanks for quick response please find the schematic attached. There are three unspecified blocks (level converter and two High Side drivers) but everything works fine.

I tested regulator simply shorting SHDN pin to ground and it’s shutdown like expected.

The +5V is delivered to all circuits on the PCB with quite wide track (32mil). The PIC has own +5V LDO regulator.

There are plenty of ground around regulator and generally on the board - I’m using ground pour fills wherever possible - with fields of vias connecting top and bottom layer. Please take look at images attached.

Something is strange for sure. I just connected spare D24V6F5 driver to 12V and diode with resistor on +5V output. Shorting SHDN to ground shutdown regulator. But touching with finger / tweezers don’t shutdown driver but with multimeter does. Only for a moment. Please look at video attached. When the multimeter is firmly attached the regulator works OK - but the voltage on SHDN is only 1,75V. Maybe I should pullup it to +5V ? But in my circuit the PIC output is driving the pin high or low.

Any thoughts ?

Slawek

Schematic.pdf (64.7 KB)

https://photos.app.goo.gl/kAg4HZYwvAH4JeBb7

Since the regulator shutdown properly when you connected it directly to ground, I think you should double check that your PIC pin is set to an output and correctly outputting high and low without the regulator attached. It is possible that your meter has enough stray capacitance to pull the SHDN pin low when it is connected. Adding a 100k pull up to the SHDN pin would probably help that and let you better monitor the behavior while the system is connected.

-Claire

The output track from PIC is simple and short

.
PIC is properly soldered and programmed - I’m using MCC - so setup a pin as output is simple and straight - hard to be wrong. The PIC is outputting 0.06V as low and 4,67V as high. Was checked with multimeter, oscilloscope (I was looking for noises) and soldered LED with resistor. I will check the pull up 100k resistor and let you know the results.

Hi Claire, I have updated report from the battle field :wink:

I was not able to shut down driver directly from PIC output pin even in OD mode. So I decided to modify my schematic as bellow:

One N-MOSFET, 10k resistor on gate (just in case), 100k pull up resistor to +12V and voila !
It’s working like a charm.

The soldering was tricky as I had on my drawer only smd mosfet, resistors are 805, but the result on pcb is almost invisible :slight_smile:

In the future projects I will be not even trying to tie SHDN directly to PIC outputs. Lesson learned! But I still have no idea why it doesn’t work?

From my perspective we can close the topic. Thank you for your effort.

Sławek

I only expect a MOSFET like that to be necessary if the SHDN input required more current than the PIC I/O could sink, but the SHDN pin current should normally only be a few microamps, so I am not sure why you were unable to shut down the regulator with the direct PIC connection. However, I’m glad to hear you found a solution.

-Claire