My question is to find whether there can be a definitive answer to this particular part.

I have Cypress MBR3002 IC which has two power pins labelled VCC and VDD.

I got a question from my colleague about the reason behind two different names for two power pins.

According to datasheet, VDD is actual power pin and VCC is internal to the IC. At lower supply voltage, both needs to be supplied by external supply itself. At higher voltage VDD is internally derived by the IC using external VCC.

I had this great answer about terminologies and I was able to answer on similar lines.

But, I would like to know if there are any good reasons for the labels VDD and VCC in this particular IC only.

Edit: Should I drop this search right now and see other important stuff?

  • \$\begingroup\$ here lies your answer reference.com/technology/electronics-vcc-stand-7b80e7fc82dca54e \$\endgroup\$ – JIm Dearden Jan 6 '17 at 14:58
  • \$\begingroup\$ @JImDearden I don't think that is the real answer. Otherwise what would Vdd and Vee mean? As I knew it, doubling the terminal letter was established long ago as a convention to indicate power rails. Vcc would mean the power rail powering the collector terminal. Vdd the power rail powering the drain. Vee that powering the emitter. etc. \$\endgroup\$ – Lorenzo Donati Jan 6 '17 at 15:03
  • \$\begingroup\$ @LorenzoDonati I think the great Wiki would back me up here en.wikipedia.org/wiki/IC_power-supply_pin. (see 'the History') - Labels are simply made up by someone at some point in time and then adopted by common usage. There is only the meaning we give to them. \$\endgroup\$ – JIm Dearden Jan 6 '17 at 15:27
  • \$\begingroup\$ @JImDearden Sorry if I wasn't clear: I was arguing about the explanation given in the first lines of the link you posted: VCC stands for "voltage at the common collector, which imply that CC stands for "common collector". I think that is not how the terminology evolved historically. See this good detective answer delving into a 1965 IEEE standard.. \$\endgroup\$ – Lorenzo Donati Jan 6 '17 at 15:33

Often VDD is used for the supply of digital circuits which are mostly CMOS where NMOS have a Drain which is where the DD in VDD stands for.

Likewise analog circuitry used to be made using Bipolar transistors where an NPN has a Collector which connects (often through a resistor) to VCC.

This could result in

VDD for digital and or the whole chip

VCC for (internal) analog circuits

The fact that on this chip the VCC is derived from VDD via an internal LDO supports this, probably the analog circuits need a more stable supply hence the on-chip voltage regulator.

But as mentioned, these naming choices are quite arbitrary and are also based on history and easy naming as not to confuse the customer.

  • \$\begingroup\$ The chip definitely has analog circuitry, it is a touch controller. That makes more sense. Thanks \$\endgroup\$ – Umar Jan 6 '17 at 16:11
  • \$\begingroup\$ The analog vs. digital distinction is irrelevant - digital parts used to be bipolar too, while some analog ones are MOS, and it is the bipolar vs. MOS distinction which is relevant. \$\endgroup\$ – Chris Stratton Jan 6 '17 at 16:35

Most probably the needs for two different pins arises because that chip needs an internal 1.8V power rail, which is connected to Vcc. If the main power pin (Vdd) is powered with high enough voltage, the internal rail is derived automatically with an internal regulator block. If the Vdd voltage is too low, the internal regulator cannot work, so the datasheet simply tells you to join both pins together.

enter image description here

  • 1
    \$\begingroup\$ Yes. But, it would have been named as VDDINT.. any reason naming it as VCC. The internal regulator feature I have got it in the question already... I was thinking rationale behind it calling VCC \$\endgroup\$ – Umar Jan 6 '17 at 15:07
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    \$\begingroup\$ @Umar Your doubt is about naming? Really? Only the chip designer(s) could answer that! Maybe because Vcc is simpler? Maybe because many chips needing two positive power rails usually use Vdd and Vcc? Principle of Least Surprise? Who knows! \$\endgroup\$ – Lorenzo Donati Jan 6 '17 at 15:10
  • \$\begingroup\$ your answer is good. i reread after a year \$\endgroup\$ – Umar Jan 17 '18 at 7:29

VCC is an odd choice for a CMOS chip. I think the C is supposed to stand for "core". As Lorenzo says, it's the core voltage. Personally, I'd have called it VDD and named the external supply pin something else. Maybe they thought it would confuse people if VDD didn't need to be powered directly.

This might be a Cypress convention. You could check some of their other datasheets and see if they use the same names. Regardless, I don't think there's a good reason.


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