PMICs cut thermal stress in phone, tablet processors

ams AG has announced a power management IC (PMIC) that the company said features an innovative remote-feedback circuit that helps reduce the thermal stress of applications processors in smartphones and tablets. When paired with AS3729 point-of-load regulators from ams, the highly-integrated 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 firm stated.

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. Thanks to a patent-pending design innovation by ams, the feedback interface to the AS3721 only requires 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 layouts of space-constrained devices such as smartphones, tablets and notebooks. This dramatically 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.

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?F and at an output voltage of 1V, the system's voltage drop during a step up from 0.5-5A in burst mode is just 32mV (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).

The AS3721 PMIC features 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 8 x 8mm BGA package has a pitch of just 0.5mm.

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

The AS3721 PMIC and AS3729 power stage are available for sampling. The AS3721 is priced at $2.65 for 1,000 pieces. The AS3729 is priced at $0.40 for 1,000 pieces.