Why are PMICs gaining so much attention? Increased power subsystem complexity and, paradoxically, reduced power consumption is causing PMICs to be far more intelligent. In a simpler day of digital design, chips ran on one power supply – Vdd on schematics. Mixed signal requirements including analog inputs, high voltage peripheral drivers, and varying stages of digital logic gave rise to multiple power supplies to a single integrated chip.
Different subsystems of a device also have different power requirements, all supplied from a single battery source. These power supplies also typically have sequencing requirements such that everything initializes correctly and no damage is incurred from incorrectly applying power to interconnected circuits. In a device such as a smartphone or tablet, some of these unique power requirements are seen clearly:
Another aspect of power management is seen in the lower left corner: many devices have recharging capability, sometimes with an advanced wireless power transfer scheme, which must be carefully coordinated. A good example: my Samsung Galaxy S7 charges wirelessly without any problem, but my wife’s Galaxy S6 which allegedly uses the same wireless charging standard is extremely finicky and aborts charging when the display turns off.
That’s just one case in point of power domains within a device, where areas of circuitry power down to save power – hopefully without adversely impacting operation of other functional blocks. Modern PMICs also usually contain state controllers so they can correctly respond to full power and reduced power modes of the system. It’s non-trivial. Occasionally, my Verizon Ellipsis tablet seems to lock up in a mode where its Wi-Fi doesn’t sleep even though there is no other activity, and rapidly and completely discharges the battery.
There are also thermal considerations, where power demand needs to be managed based on operating temperature. Recent news of total recalls of the Intel Basis Peak smartwatch and the McDonald’s Step-It fitness tracker, both for inducing discomfort or even blistering due to localized overheating, suggest wearables may be the next frontier for power management. Designers of wearable and IoT devices may need to trade performance for thermal conditions in ways that existing chips haven’t quite imagined yet, particularly when transitioning from recharge to discharge modes.
Relying on system-level software to manage the minutia of power management misses huge opportunities and often leads to deadlock at inappropriate times, which can completely undo any power savings or worse lead to a safety condition. This is noteworthy in automotive platforms, connected to the ultimate battery system delivering power to many electronic subsystems. Every one of those subsystems has to manage itself, intelligently, if both system power and functionality are to be as expected at all times.
Building a more intelligent PMIC that meets the needs of both device manufacturers and device users is a challenge. Unique requirements are driving more teams toward customized PMIC chips implemented with one-time programmable (OTP) memory. Using OTP has several advantages. Implementations are compact and tamper-proof compared to microcontrollers, without storage endurance considerations. If a requirement changes, designers can modify the OTP configuration quickly, similar to programmable logic devices but much less expensive. OTP macros from Sidense also support mixed-signal, high-temperature processes typical of automotive environments such as 180nm BCD.
Sidense also offers the integrated power supply (IPS) macro, generating bit-cell programming from available power supplies. The OTP and IPS macros can be designed into a mixed-signal PMIC easily, providing the exact functionality needed in less silicon area at a lower cost than alternatives.
The same factors that are leading to purpose-built application processors for automotive, IoT, mobile, and wearable applications mean companion PMICs customized to system requirements are also needed. Avoiding bad power-related behavior with good PMIC design helps devices achieve success – it’s a huge factor in perceived reliability and trust. Teams looking for more differentiation and control are turning to OTP macros for customized PMIC designs.