S12ZVC HW design for CAN & ADC

[daehyeonkim]

Dear sir,

I have a question about the CAN, ADC hardware design for S12ZVC MCU.

actually, this is my first time to use this MCU. I didn't receive yet and need to design HW before that.

accordiing to the datasheet and the hardware design guide document, S12ZVC has an internel voltage regulator.

on the datasheet, the voltage source for the voltage regulator(VSUP) can be 12V/18V.

this pin is connected to the other power source pins through the base control external PNP transistor(BCTL)

so, I think that the rest of power pins such as VDDX, VDDA, VDDC will be 12V/18V also like VSUP.

but VDDA is for ADC, VDDC is for on-chip CAN transceiver,

datasheet said that it needs 5V on VDDC. also, VDDA is the reference high voltage for ADC.

if this is not, do we need an additional voltage regulator for this?

I attached the one part of the hardware design guide on here.

Thank you.

[RadekS · Accepted solution]

Hi Daehyeon,

This is juts misunderstanding.

The external PNP transistor(BCTL) do not work as a switch but as the regulator in the linear area. The MCU drive current trough BCTL pin for achieving 5V at VDDX pin.

The similar situation is valid also for VDDC and BCTLC pin. The VDDC provide next 5V power supply independent on VDDX.

The VDDA have to be externally connected to VDDX.

In fact, for VDDX you may choose between internal power regulator (the generated heat ((VSUP-5V)*IDDX) have to be dissipated by MCU) or external power regulator (the generated heat will be to be dissipated by external QPNPX transistor).

Both regulators (internal and external) are enabled by default after reset, but the external regulator has slightly higher target voltage. Therefore the VDDX will be driven by external regulator when external PNP transistor is assembled.

If you want to use VDDC power regulator, you have to use external PNP transistor.  

I hope it helps you.

Have a great day,
Radek

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