Hello,
I want to use the ATD on the MC9S12D64 with an external reference voltage. I want to use the LM336-5.0 as a 5V reference voltage. It has an operating current up to 10mA. No i want to connect this voltage to the Vdda and the Vrh Pin, but I am not sure if this is possible. What is the highest current for these two Pins?
Is it the 2.5mA like the digital I/O's? Then i could use it this way, or not? I'm really new in building Hardware, so i would be very thankful for an answer.
Just if it is important: Vregen, Vddr,Vddx, BKGD and Reset i want to supply by a different voltageregulator.
This is what my Power supply looks like:
Sorry for my bad english. Thanks and regards,
Thomas
Thank you Gordon,
so you would recommend, to connect the output of the 7805 to at least Vdda and only Vrh to the LM336-5.0? Then it could be possible that Vdda is smaller than Vrh, which would lead to an error, right? Or is the extern reference Voltage not necessary? Then i would just use the 7805 for everything (Vddr, Vddx, Vdda, Vrh, Vregen, BKGD and Reset). Which way would you prefer?
Sorry, thank you for your time and the answer.
Thomas,
The 2.5 mA you reference is the injection current limit (i.e. when an I/O pin exceeds VDD + 0.3V or VSS - 0.3V). As long as an input pin is within VDD + 0.3V or VSS - 0.3V it is very high impedance and will only draw leakage current levels (see specifications). For VRH, the MC9S12DJ64 Device User Guide — V01.20 in Table A-8 specifies 0.375 mA for one A/D block enabled and 0.750 mA for two A/D blocks enabled.
I would not recommend connecting the output of the LM336-5.0 to VDDA unless the main regulator has better than 2% tolerance. This is because of parameter ∆VDDX in Table A-4 which states that Voltage Difference VDDX to VDDR and VDDA is to be no more than +/- 0.1V.
Also, make sure you have the proper bypass capacitors on all of the supplies as detailed in Table 22-1.
Regards,
Gordon