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Tell Me Why My Smartphone Requires 30 Voltage Rails

In my experience, mixed-signal ICs with high levels of integration fall into two categories. The first is the chip designed for a very specific application, often just for one end product. The other category includes ICs for general use in many different end products with similar needs.

For the first category, consider the PMICs for smartphones that my current employer has been quite successful with. Cleverness is required in integrating many functions into a small number of chips in a very short period of time. I do not work in this part of the company, and frankly, was shocked to recently find out how many voltage regulators are integrated into these devices — thus the request at the beginning of this blog.

It takes no small amount of engineering cleverness to integrate so many regulators with other, often quite dissimilar functions, and to do so economically and quickly. Frankly, I am amazed that these guys pull this off at all. And they do so regularly.

A different kind of cleverness is needed in developing integrated chips for a range of applications and/or end products. In this case, there are multiple end targets with different requirements. As the level of integration increases, the breadth of end targets narrow but, qualitatively at least, the problem is the same; there are many target end products for the chip to be designed into… if the developer is clever enough.

Let's go back to the dark ages (the early 90s) when I was designing microcontroller-based consumer products at a startup. If we were a larger company, we could have had a customized version of a microcontroller made with the peripherals and amounts of RAM and ROM (no on-chip flash yet) that suited our needs.

Instead, I had to look at the microcontrollers available, with each family having parts with different levels of integration. Some had nearly everything we needed, but also had a lot of what we did not need and thus cost too much. I had to balance the cost of implementing functions external to the µC vs. the cost of having too much integrated. This is an interesting trade-off to have to make, especially when a few cents difference can make or break a product.

The developer of more general integrated products has to run this thinking in reverse while predicting the future. And, as the wise old man Yogi Berra once said, “It's hard to make predictions, especially about the future.” This developer (not Yogi) has to look at a range of yet-to-be developed products and determine the optimal combination of features. If he integrates too much or too little, the product will not be successful. Like the third bed in Goldilocks and the Three Bears , it has to be just right.

Success with this type of product requires a good understanding of the markets for the end products that such chips will go into as well as a good understanding of the available technologies at hand to implement these chips. Once again, integration calls on the chip developer to not only know his business but his customer's business as well.

7 comments on “Tell Me Why My Smartphone Requires 30 Voltage Rails

  1. Doug Grant
    February 19, 2013

    The problem is that the digital stuff drives everything else. Powr is always an afterhought…”oh, we'll just add another regulator if we need one – they're cheap and small, either integrated or discrete”. Those 30 rails probably include 10 different voltages for the various processor cores, each separately enabled to save power when that particular core isn't needed. Then separate rails for the I/O drivers and memories. Then additional rails for the mixed-signal and RF sections, each with a different voltage and a low-noise LDO fo rthe VCOs. Ah…for the good old days of a single digital rail…and one or two for the analog stuff.

  2. Mark Fortunato
    February 19, 2013

    Doug, yes, I remember those days well.  5V and +/-15 was all we needed.  But then didn't we have to hand-crack our cars to get them started back then?

  3. SunitaT
    February 20, 2013

    Mark,

    Multiple voltage rails are required to drive a variety of device loads spread across the IC. The digital electronic components and circuits such as motherboard, adapter cards, and disk drive logic boards typically use the power supply of 3.3V or 5V whereas motors like disk drive motors, high-output voltage regulators use the 12V power.

  4. RedDerek
    February 20, 2013

    Multiple rails are for different systems. When I was marketing manager and working with digital camera folks, look at the supply count: + and – for the LCD, plus a bias for contrast, uP gets a supply, on-board memory another, flash memory insert gets another, two more for the CCD, and so-forth. Early products start with assembling different technologies into one device. As technology improves, newer voltage supplied products come out so that similar voltages can be used and thus reduce power rail count.

    And, as said earlier… power supplies are more of an after-thought. Making power supply design fit the left-over space is the joys of designing.

  5. amrutah
    February 21, 2013

    Mark,

       The battery pack is usually 3.7V, atleast the one that I have (Google Nexus One).  I dont understand the place where we need 30V so that we boost the 3.7V volts to 30V.  The micro SD card, SIM card, GPS and WiFi work at near to 5V.

    I thought that there might be places like the EEPROM inside a chip that might need some high voltage (a charge-pump like module might be suffcient to raise a momentary high voltage).  

    I really dont understand where the Voltage rails are 30V inside my smartphone?

  6. Mark Fortunato
    February 21, 2013

    Amrutah,  I think you misread the title.  I was not talking about a 30 volt rail (a supply of 30 volts).  I was talking about the phone having 30+ rails requiring 30+ regulators.

  7. amrutah
    March 1, 2013

    Mark,

       My mistake, I completely misread it.

    I have worked on PM chips which has somewhere around 10-11 LDO's, 3-4 switchers for supply rails and around 8-10 grounds (reference ground planes), which in itself is very complex considering: handling amps of current, the chip temperatures (hot regions), the associated clocking scheme, digital for powerup sequencing and so on…

      Integrating 30+ voltage rails is a stupendous jobs which will invite a lot of accolades!!!

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