GPIO electric properties and example circuit diagrams ?

Hi,

I need some hints related to the electric properties of GPIO
interface.
I want use 4 GPIO pins in output mode, but I'm not so experienced in
hardware design.
I want trigger a relay and I think I have to use I driver IC.
What would be a good driver IC's ?
Are there some documentation related to hardware aspects with example
circuit diagrams ?

Best regards

Andreas

Hi,

I need some hints related to the electric properties of GPIO
interface.

These are documented in the technical reference manual.

I want trigger a relay and I think I have to use I driver IC.
What would be a good driver IC's ?

If you want something easy you can just use a simple NPN transistor with
a diode and a resistor.

Small signal NPN transistor. Most will do. Rule of thumb: In the
datasheet of the transistor the hFE should be > 150, and Ic >= 300mA. I
like the BC337.

Connections:

Emitter to ground
Basis to the GPIO via a 1KOhm resistor
Collector connects to the relay-coil.
The other side of the relay coil goes to the relays supply voltage.

Important: You need a protection diode across the relay coil in reverse
direction to protect the transistor. Cathode of the diode connects to
the relay supply voltage, anode to the collector of the transistor. A
1N4148 will do.

This simple circuit works pretty well for small 5 to 12V relays that
take up to 100mA current for switching.

Since you're not a pro one word of advice: Check the specification of
the relay. Don't exceed the maximum ratings! a relay may work for a
while over spec but may have a catastrophic failure later. You don't
want to burn down our house because you have an electrical arc in a 24V
relay that switches mains voltages.

Cheers,
    Nils

Hello Andreas,

I use 2 GPIOs to drive an LED.
I have been using a PMOS transistor (BSS84P from Infineon). A maximum
of 170mA can flow from source to drain, the Vds(max) = 60V.
Instead of using an NMOS transistor, I have just used a resistor in
parallel with my LED and it works just fine.

To set the GPIOs, you will need to take a look in chapter 7 and 24 of
"OMAP35x Applications Processor, Technical Reference Manual".

You have do to the pad configuration as it is shown on Figure 7-7,
page 752. The GPIO registers can be found on Table 7-4.

On Chapter 24, you can find the registers you have to set. As an
example, the register that determines if the GPIO will work as Input
or Output is shown on Table 24-27.

Regards,
Frederico