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PMIC reduces thermal stress in smartphone, tablet processors

30 May 2013  | Steve Taranovich

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Ams has recently unveiled its latest power management IC (PMIC), the AS3721. The PMIC includes a remote-feedback circuit that helps reduce the thermal stress of applications processors in smartphones and tablets.

The company's PMIC enables a compact remote feedback path from the processor to the IC's integrated DC-DC controllers. The feedback interface to the AS3721 needs 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 far apart in the board layout in space-constrained devices such as smartphones, tablets and notebooks. This reduces the size and intensity of 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. Not good for processor performance or reliability.

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 40µF 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 32mV (typical).

When paired with AS3729 point-of-load regulators, the AS3721 provides a complete power management system that gives a fast response to load transients for reliable processor performance, high efficiency, and flexible board layout.


Figure 1: The AS3729 power element is a partner IC that completes the power management circuit with the AS3721.

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).

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

The AS3721 PMIC contains four DC-DC step-down regulators supplying 4A, 2A and 1.5A; three DC-DC step-down controllers rated for 5A, 10A and 20A; 12 digital LDOs; a real-time clock; a supervisor circuit; GPIOs; a general-purpose ADC; and a one-time programmable boot sequence. The device's 8mm x 8mm BGA package has a pitch of 0.5mm.

The AS3729 power stage is in a chip-scale package measuring 1.6x1.6mm and with a 0.4mm pitch.

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