Hi Zaiqiu,
It depends ….
1. on the power supply. S12G RM specifies minimal VOH as (4.2V) for current -4mA and 5V power supply (see Table A-8 and Table A-9). S12G RM specifies minimal VOH as (2.9V) for current -4mA and 3.3V power supply (see Table A-6 and Table A-7). These values are worst cases with some safety gap, but it still mean that values of the output voltage may be strongly influenced by this current.
2. on total consumption and selected MCU package. The maximum current for single power supply pin is +/-60mA (See Table A-1). So, if we have MCU with just one VDD pin (like VDDXRA), the total consumption of MCU include loads should be below these 60mA. The same is valid for VSS (VSSXA) pins.
Note: CPU is powered by VDDR domain, ports except AD are powered by VDDX domain, port AD and analog modules are powered by VDDA domain.
3. circuit protection. Relays are inductive loads which may generate spikes…
Shouldn’t be better use some MOSFETs or directly switches?
Automotive MOSFETs|NXP
MOSFETs|NXP
Another option is using S12VR MCU with integrated two low side drivers to drive inductive loads and powered directly from 12V (for higher inductive loads is here MM912_634).
Note: The rest of MCU is very similar to S12G family.
S12VR Mixed-Signal MCU|MagniV|NXP
HCS12 Based Relay Driver with LIN|NXP
I hope it helps you.
Have a great day,
RadekS
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