System-in-package boosts AC-DC power density

August 10, 2021 // By Nick Flaherty
System-in-package boosts AC-DC power density
Silanna adds GaN support via a register programmable gate driver to its SZ1131 active clamp flyback AC-DC controller

Silanna has launched an AC-DC converter system-in-package to reduce the size of AC-DC USB chargers and cut the no load power consumption

The SZ1131 fully integrated active clamp flyback controller combines four functions in the package and supports either silicon or gallium nitride (GaN) switching FETs via a software programmable driver.

“By integrating two devices into a single package, the SZ1131 delivers the functionality of adaptive digital PWM controller with an ultra high-voltage (UHV) active clamp FET, active clamp gate driver and startup regulator. It’s a single device with a discrete FET – one of our IP is on how to use a lateral FET to improve the efficiency. We use a derivative of lead frame mounting with additional steps to make sure of the reliability.”

This SIP approach cuts the bill of material for a USB charger by 10 devices and increases the power density.

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“This is a result of more integration in the IC, improved programmability on the gate driver so you can select the right level for the primary side FET and no longer need an RC snubber on the primary side as well as transformer saturation protection as the device will detect a fault and protect the system. In addition we have advanced digital control over changing line load and temperature conditions and allows wider component tolerances to simplify the design,” he said.

The design uses a burst mode operation for low load and no load. This allows a no load current under 15mW for a 33W charger with 20mW for a 65W design. “We power down a lot of non-essential modules and reduce the clock to 25kHz just to make sure it’s not audible at no load, and we have other proprietary modes to reduce the EMI even further,2 he said.

Silanna has built a reference design for a 65W, 20V single output charger with 30W/in3 power density with a fully silicon design using a 100V FET rather than a 120V device that has a 19.8mW standby current at 230Vac. A 33W charger design has a standby current of 13mW.

Engineering samples  are now available with full production Q4 21. The PD Hero design tool can be used to email back a full schematic with bill of materials.

www.silanna.com

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Picture: 
The Silanna SZ1131 active clamp flyback AC-DC controller in a 65W USB charger reference design

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