Rapid charge AC/DC controller conforms to Mediatek Pump Express

March 03, 2014 // By Graham Prophet
Designed for China’s smartphone market, Dialog’s iW1680 uses built-in digital intelligence to enable rapid charging at no additional BOM cost versus slower conventional chargers

An AC/DC rapid charge controller compatible with MediaTek’s new Pump Express fast charge protocol, the iW1680 is a single-chip solution that uses Dialog’s intelligent rapid charge digital algorithm and digital primary-side control technology to significantly reduce charge times in USB AC/DC wall chargers with no bill of materials (BOM) cost premium over slower conventional charging technologies. “Pump Express” is MediaTek’s proprietary protocol for fast charging mobile devices, including feature phones, smartphones and media tablets, up to 45% faster than conventional chargers.

Conventional USB chargers provide a fixed 5-V supply that requires a buck converter inside the handset to convert the 5V down to the required output voltage. The iW1680 uses Dialog’s built-in, intelligent rapid charge digital algorithm that communicates with MediaTek Pump Express-compatible phones and dynamically scales the output voltage of the wall charger to deliver the optimised level required by the phone at any given time. This lowers the overall system cost by eliminating the need for an input buck converter in the phone and reduces charge times by enabling more efficient power transfer to the phone battery.

Building on Dialog’s accurate primary-side control for AC/DC power supplies with its PrimAccurate primary-side controller platform, the iW1680 rapid charge AC/DC controller embeds digital analysis on the primary side of the isolated power supply within the charger. This allows voltage scaling without the need for any intelligence on the secondary side and further reduces costs.

The iW1680 supports power adapters up to 7.5W, with high active average efficiency and low no-load power consumption less than 30 mW. Communication between the phone and iW1680 is through the VBUS supply line. Voltage scaling is digitally managed on the primary side of the transformer in the AC/DC adapter by the iW1680, which analyses the signal of the VBUS and scales its output voltage accordingly. The iW1680 easily and efficiently drives low-cost bipolar junction transistor (BJT) switches to further drive down BOM costs and reduce