Power management chip spreads thermal load in compact designs

May 29, 2013 // By Graham Prophet
Helping to reduce thermal stress on processors in phones and tablets, a new-architecture IC from ams enables board designers to physically separate the PMIC and the applications processor.

ams (formerly austriamicrosystems) has introduced the AS3721, a power management IC (PMIC) with a remote-feedback circuit that helps to distribute the heat dissipated in small-outline designs such as smartphones and tablets. When paired with ams' AS3729 point-of-load regulators, the AS3721 provides a complete power management system that offers a fast response to load transients for reliable processor performance, high efficiency, and flexible board layout.

The AS3721 and AS3729 are optimised for use with Tegra applications processors from Nvidia.

The AS3721 PMIC enables a compact remote feedback path from the processor to the IC’s integrated DC-DC controllers, using a proprietary feedback connection that requires only two wires (one control signal, one temperature signal) instead of the four or five wires typically required by other PMICs.

With fewer traces connecting the PMIC to the point-of-load power stages, the two devices can be placed further apart in board layouts, to reduce the hotspot around the processor compared to conventional power architectures in which the processor and PMIC, both handling high currents simultaneously, must be located side-by-side. The feedback loop carried over the AS3721’s two-wire interface also operates extremely fast, maintaining the processor it supports within its safe operating voltage even when supplying extremely fast-changing loads. Using an output capacitor of just 40 µF and at an output voltage of 1.0V, the system’s voltage drop during a step up from 0.5A to 5A in burst mode is just 32 mV (typical).

The AS3729 5A point-of-load power stages complement the AS3721 PMIC. The AS3729 contains NMOS and PMOS FETs for each of two phases, which can be controlled separately and can handle an output current of 2.5A. The PMIC can combine up to four devices in an eight-phase configuration that supplies a 20A maximum output. By choosing single- or multi-phase configurations, device manufacturers can optimise their design either for cost and board footprint (using fewer, larger inductors) or for low profile (using more, smaller inductors).