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GPIO High On Powerup | Cypress Semiconductor

GPIO High On Powerup

Summary: 7 Replies, Latest post by odissey1 on 23 Nov 2016 06:15 AM PST
Verified Answers: 2
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DiodeBridge11's picture
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25 posts

Hello,

In one of my projects, I am using GPIO pins to drive a ULN2003 Darlington transistor array. The transistor array drives some LED lamps and two relay coils.

When power is first applied to the circuit, all the lamps and the relays come on for about 100mS then go into their initial states (low for all in this case).

Is there any way I can force the GPIO pins to be low even on power up? If it requires a hardware change, I am open to that because I need to do a board spin anyway.

I do not know if the paragraph below is relevent, but...

My digital power supply uses 3.3 volts and the analog system uses 5 volts (along with VDDIO3 and VDDIO0). The relays switch mains voltage so I do not want interment turn on. The power supply for the system uses 3 linear regulators. A 24 volt power transformer feeds a 12 volt regulator. The 12 volt power feeds the LEDs and relay coils which are switched by the ULN2003 chip. The 12 volt regulator feeds a 5 volt and 3.3 volt regulator for the logic digital and analog power supplies. There are two 6800uF capacitors on the power input to allow for delayed power off.

Magnus Lundin's picture
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32 posts

You could try to use a weak external pulldown (3-10k)

user_1377889's picture
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9583 posts

For PSoC5 there is a pins option "reset" which allows for programming an initial state before the pin's drive mode get initialized.

You may select a "Pulled low" option.

 

Bob

DiodeBridge11's picture
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25 posts

Thanks.

I will give that a try.

DiodeBridge11's picture
User
25 posts

I set the pins to pulled low. All the GPIO pins still remain on at powerup but they remain on for much shorter.

Does this have something to do with using both 5V and 3.3V?

user_1377889's picture
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9583 posts

The pins shouldn't be "on", they probably are in "high Z".

There is a small time where the level is not determined from startup until the supply voltage reaches the minimum operating voltage of 1.7V.

 

Bob

DiodeBridge11's picture
User
25 posts

The issue is more of an annoyance in this situation that a show stopping problem. I can see how this can be dangerous in a safety critical system. In my situation, all I need to do is add an RC network on the relay coils to stop the mains voltage from momentarily being switched to my other circuitry. If I do not do this, the life of the relay will be shortened due to the momentary switching arcs. As for the LED lights, it does not matter so much.

user_342122993's picture
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579 posts

You don't need RC on outputs that power relay coils with huge inductance and low resistance. What you really need is clamp diodes to suppress backslash current to protect PSoC.

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