ADS1258: ADS1258 Crystal Startup Problems

Thank you, Chris! Are you absolutly sure, that XTAL1 is input?

About start-up issues: I think, there is a mistake in datasheet, usage the 32768 Hz crystal in the same style as high frequency crystals. 32768 usualy need additional phase shifting circuit, as series resistor and shunt capacitor; without this circuit start-up issues for 32768 is normal. May be, this oscillator have internal series resistor?

Hi Nick,

I confirmed with design and layout that XTAL1 is the crystal driver input.

I also didn't see any internal series resistance added on the XTAL2 output; however, the output current is internally limited so this may have a similar effect to some degree... Being current limited, I know that you don't need the external resistor for limiting power dissipation across the crystal, but I was not aware that it might be needed to produce an additional phase delay. Thanks for that info!

When the ADS1258 was originally tested with several crystals no additional resistance was added in series, so it can work without an additional resistor if the load capacitors are adjusted properly. If I were you, I would probably go ahead and add in the series resistor between the crystal and the XTAL2 pin since you can always adjust the value.

If you do try out different resistor values, I would be interested to know what you find works best!

Best regards,
Chris

Thank you, Chris! I'll write about results at month or two (this ADC is a little part of big project). I need to use it in full temprature range, and have some restrictions with crystal choise; so, I can't use crystals with garanteed low ESR.

Series resistors in this kind of circuits (low voltage, high input impedance) more important for additional phase shifting, then for power limiting. It's strange that this resistors (phase shifting and biasing) is presented in the ADS1241 datasheet, but not in ADS1258, which have near the same oscillator.