Looking at PMICs: Wider Input-Voltage Range Yields Better Designs (& BOMs)

In a design world that sometimes seems focused on operating from supposedly tightly bounded sources such as nominal 12 V and 24 V battery packs, it's nice to know that there is still plenty of need for regulators that can handle wider input swings.

This became clear when I saw a recent blog (“Why Wide VIN ICs for a 12V or 24V Rail ?”) and associated whitepaper (“Wide VIN Power Management ICs Simplify Design, Reduce BOM Cost, and Enhance Reliability “) from Texas Instruments, which discussed the ongoing need for designers to use input regulators that can handle wider VIN spans, despite the apparently limited range of DC input to the regulators in many cases. It turns out that many of these DC sources aren't so narrow-range after all, in real-world areas such as communications, industrial and automotive applications, even if they are supposedly well behaved.

To bolster the case and go beyond anecdotes, TI cited results from a 2012 study by Databeans Inc., which showed that 35% of PMICs (power management ICs — controllers and regulators) are rated above 20 V (See figure). Though it doesn't say so, I suspect these results are based on unit volume, so there would be a heavy weighting due to the high volume of genuinely low-voltage/low-input-span applications on handheld devices. I think if you looked at it in terms of application areas, the proportion of PMICs over 20 V would be much, much higher.

Despite our concentration on low-voltage design, 35% of PMICs are rated at 20 V and higher.(Source: 2012 Databeans Incorporated.)

Despite our concentration on low-voltage design, 35% of PMICs are rated at 20 V and higher.
(Source: 2012 Databeans Incorporated.)

Why use PMICs with wider input range? The TI piece cites several reasons: applications where the input rail is allowed, by definition, to have a wider span (PoE, for example); those where transients are common (industrial and medical); and those where a rare transient may occur and cause system damage (a system which may see sporadic EMI-induced transients). For some designs, it's primarily of design insurance and peace of mind, usually leading to long-term overall reliability.

While it is possible to add external protection to a PMIC using one or more surge protectors and clamp components, that adds to design challenges, as well as BOM complexity and cost. Using a wider VIN PMIC may also allow the designer to re-use a selected PMIC, with its known characteristics and idiosyncrasies, in multiple places (one less thing to “surprise” the engineer); doing this would also simplify the BOM.

Have you ever wished you had used a PMIC with wider range for VIN ? Conversely, have you ever had to justify the decision to do so, in a design review or BOM review?

A somewhat-related question: whatever happened to the push for use of 24 V DC rails in cars, which began with lots of attention and then fizzled out about 10 years ago? It was clear that the standard 12 V rail was inefficient for delivering all the amps that today's cars need, for both their basic operation and all those added safety and entertainment subsystems.

As a result, there was a push to go to 24 V via two batteries, standards were defined, and many leading vendors released critical parts (e.g., PMICs, FETs, switches) for the higher voltage rail. Yet today's cars still use 12 V for all their basic DC rail needs. Is there a single, dominant reason that 24 V never caught on, or was it due to a combination multiple reasons (e.g., space, cost, universality, or reduction in needed amps due to lower-power electronics)?

I'm just wondering what you think the reasons were. No one seems to be interested in the subject any more, but we can learn from these recent situations and predictions which proved incorrect.

This article originally appeared on EDN.

2 comments on “Looking at PMICs: Wider Input-Voltage Range Yields Better Designs (& BOMs)

  1. _hm
    November 23, 2013

    Wider Vin is a design trade-off. It does not come free in real sense. At some point in design one is compromising another aspect of design. When power vs size vs thermal management is relaxed, yes, that is good. But one needs to consider real need of design and not just employ widest Vin parts.


    November 24, 2013

    A PMIC with a wide Vin range is more expensive than a low Vin range.  This is because the power devices needed to standoff the voltage are much bigger and hence more expensive.  Only low volume customers are willing to pay for this.  High volume apps will always use PMICs with the Goldilocks Vin range.  I would take the TI assertions with a large grain of salt.

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