Powe supply with VDDXR and VDDA/VRH for 9s12GA48

[jianglei]

Hi all, 

I want to use a voltage reference chip ( REF3040, output reference voltage is 4.096V, Maximum output current:25mA) to supply VDDA/VRH (Pin 37). The VDDXR (Pin 2) is supplied with 5V. Thus, the voltage between VDDRX(5V) and VDDA/VRH(4.096V) are different. So, I want to know whether the chip can work under this condition?    

[martynek]

Hi

Unfortunately this won't work. The voltage difference VDDX to VDDA should be in range of (–6.0;  0.3 V).

See the Reference manual in section Electrical Characteristics: Table A-1. Absolute Maximum Ratings.

VDDX and VDDA pins are connected via an ESD diode, thus the voltage drop.

Difference out of the range would cause a current flow through the diode.

The MCU allow to use 3.3V at digital part and 5V at analog, but not in opposite direction.

If you use 64-pin LQFP package, where VDDA and VRH pins are separate, you may connect VDDA to 5V and use 4.096V as reference source for VRH pin.

NOTE:

The voltage VDDA is monitored. Whenever VDDA drops below level VLVIA, the status bit LVDS is set to 1.

And VDDA Low Voltage Interrupt Assert Level is typically 4.23V.

See Table A-31. Voltage Regulator Characteristics.

This interrupt can be disabled, however, it is safety feature.

Regards

Daniel