Combined DC-DC converter and controller slashes USB PD3.0 no load power
Silanna Semiconductor has launched a combined power converter and controller for USB PD3.0 chargers that slashes the no load power consumption.
The SZPL3002A, codenamed Hammerhead, is capable of up to 27V and 65W for the PD3.0 Type C interfaces and QC2.0/3.0/4.0/5.0 support for Type A/C connections. It has an efficiency of up to 98% and includes a switch to detect no load and cut off any power except for the controller. With a high frequency up to 2MHz for a small size, this is a key step to integrating ISB PD chargers into wall sockets.
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“It’s a buck converter with a lot more icing on the cake,” said Hubie Noto, marketing director at Silanna Semiconductor. “This consists of two sections, a DC-DC buck converter with a PD controller with power sharing.”
The switching frequency for the silicon FETs is electable from 667kHz to 2MHz to reduce the size of the inductors that are needed to reduce the size of the charger. The efficiency is 98.5% at 667kHz with a 4.7uH inductor, and although that falls slightly to 97.5% at 2MHz the inductor is reduced to 2.2uH.
“We select the silicon FETs for the buck converter to optimise the efficiency so we have an RDSon of 41mΩ for the upper FET and 38mΩ lower FET all on the same 180nm die built at TSMC for a 5 x 5mm die,” he said.
“We have a power saving mode that is selectable by user that detects a no load condition so the PD will disable the power stage and there is no switching, no Vout, its just the PCD controller on to monitor the Vcc line so the consumption is in the microwatts,” he said. “It takes milliseconds to switch on during the handshaking with the load.”
The controller allows for intelligent sharing of power between ports in a multi-port charger. “The PD controller is on separate die and we license a 8051 controller on a 130nm TSMC process,” he said.
“The way we do things is anyone can plug in the C1 or C2 ports and it will deliver 60W but if you have the sink source already submitted the request for 60W is stored in the controller. If C2 wants 60W, the controller keeps C2 running so that the phone thinks it is charging but at a low level, say 2W, which enough to keep the port open. As C1 drops, the controller recognises it has more power available and rebalances the power to deliver the balance to the second port. This balancing and sharing is happening behind the scenes without the need for a handshake so there is no disconnecting.
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The company also plans to support later versions of the PD standard. “For 3.1 we need to do 28V and 48V for 3.2 and we do have this product in the works so we will jump to 3.2,” said Noto. This is likely in the next 12 months but will require a move to GaN transistors, where Silanna has a partnership with supplier Transphorm.
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