do i need resistors for spi interface?

Hello,

been playing with with one analog devices adc chips in tssop28 package.

After a whole day of operation, noticed a few ADC chip pins became dark, as if they were overheated. Checked the resistance of the soldering - no problems.

the pins which are discoloured I use alongside SPI protocol, to activate and deactivate various functions in the chip. the pins are either logic high (5V), or logic low (0V).

Is it possible that arduino outputs too much current, for their operation? there is no info in datasheet about current limits for i/o pins in the chip. Should I just simply put some resistors to limit the current? but how much to limit? 10mA, 5mA, 1 mA ? Is there an industry good practice on such things? Also, should I put resistors on SPI line as well?

Thanx

It's unlikely that just a few pins would overheat; if the darkening is due to heat then the chip as a whole has probably overheated.

You need to provide more information if you want more help, e.g. what part number ADC you used and a schematic showing how you have connected the ADC to the Arduino.

V_king: Hello,

been playing with with one analog devices adc chips in tssop28 package.

After a whole day of operation, noticed a few ADC chip pins became dark, as if they were overheated. Checked the resistance of the soldering - no problems.

the pins which are discoloured I use alongside SPI protocol, to activate and deactivate various functions in the chip. the pins are either logic high (5V), or logic low (0V).

Is it possible that arduino outputs too much current, for their operation? there is no info in datasheet about current limits for i/o pins in the chip.

No, not possible. The amount of current drawn from an arduino output pin is determined by the load circuit, in your case the ADC chip and logic input pins draw almost zero current.

Should I just simply put some resistors to limit the current? but how much to limit? 10mA, 5mA, 1 mA ? Is there an industry good practice on such things?

No, current limiting resistor are not normally required to interface logic signals. But are you sure your ADC chip is rated for +5vdc service? Some are 3.3vdc devices only. Check the datasheet to be sure as if you are overdriving a chip designed for 3.3vdc service with the +5vdc signals that the arduino uses that could be a cause for overheating.

Also, should I put resistors on SPI line as well?

Thanx

Hello,

Thank you for replies.

The adc is analog devices ad7734. I use their general circuit from datasheet (fig 29, p. 31), except I use ADR431B voltage reference. I also control RESET and CS (chip select) pins with arduino. Voltage supply for the chip is 5 Volts, which I use from arduino, with bypass capacitors.

The discoloured pins are RESET, CS and SCLK. The only difference in datasheet I can find from the other pins is that these three pins are Schmitt triggered. I have a very basic understanding about Schmitt triggers, but I do not see, how that would affect the operation of the chip.

I will try to resolder those pins tommorow and see if the problem repeats itself. It is my first project, where I am using SMDs, so it might be my shaky hands. Although after soldering, I checked all pins resistance, and everything was ok.

On the other hand, Farnell offers a heat sink in their accessories list for the chip, which I found surprising, as there is no mentioning about extra heat dissipation in the datasheet. :~

The pins were tarnished already! If the chip is working there's no way an input pin can draw significant current (at DC nA is the kind of value, pluse a few mA spikes on transistions at most).