Electronics Weekly Electronics Design & Components Tech News
For GaN-based power adaptors with USB-PD outputs, STMicroelectronics has announced an active clamp fly-back controller with a USB-PD 3.1 interface in a single package, that includes galvanic isolation between primary and secondary sides, crossed by a data link.
Called ST-OneMP, on its primary side, it is designed to work with one of the company’s GaN half-bridge-plus-driver combo ICs, communicating through the its high and low-side PWM connections and a chip-enable. Start-up power for the secondary side must come though a pair of diodes straight from the filtered live and neutral inputs (more of this later – not shown on diagram right), later replaced by a feed from an auxiliary winding on the transformer.
The secondary side is controlled by a largely inaccessible Arm Cortex-M0+ microcontroller on the die, that drives the secondary-side synchronous rectifier mosfet and supports voltage negotiation for the main USB-PD output port, and will control the PD output – but not the optional second output.
64kbyte of flash is factory-programmed to suit the intended application. USB-PD 3.1 PPS certified firmware is pre-loaded, according to the company, “permitting a turn-key solution for standard applications”. Synchronous rectifier and the fly-back converter are controlled for zero-voltage switching non-complementary active-clamp operation, “which allows high power with greater efficiency than conventional quasi-resonant fly-back”.
Not every USB-PD feature is supported: constant PPS power, communication via USB D+/D- (or SSTx± SSRx±) and fast role swap are amongst those omitted.
The only part of the controller accessible to outsiders is flash that tunes details of the power conversion, sets up application functions, chooses the protocol, and choose the way the two output ports are treated.
The reason that the primary-side has to take initial power through via diodes before the system bridge rectifier, is that the IC also provides the safety discharge necessary for the input X-capacitors, testing for for dc on the input as a sign that discharge should be initiated (therefore the IC cannot start-up from a dc source) and discharging until the voltage drops below a threshold, or ac is once again detected.
Packaging is SSOP36.
There is an associated evaluation kit, EvlOneMP (left), that combines the IC with a MasterGaN4 600V power stage to create a 65W (USB Type-C PD) + 10W (USB Type-A) ac-dc adaptor. Input is 90 – 265Vac, 47 – 63Hz.
This module measures 58x36x20mm and can hit >93% efficiency at full load. Without the USB-A port loaded, the primary port supports 5, 9, 12, 15 or 20V out, all at 3.25A, or up to the same current (‘PPS’ mode in 20mV and 50mA steps) at 3.3 to 16V, or 3.3 to 21V.
The ST-OneMP product page can be found here
