Innoswitch questions
Posted by: treez
on
Hi,
Is it possible to operate innoswitch without connecting the FWD pin?.....We dont like the 6:1 flyback transformer needed when you connect it.
What is the basis behind the switching frequency recommendations in the innoswitch datasheet...is it that the turn off losses are too high if too high a frequency is chosen?
Woudl you say the innoswitch has a more slow, controlled fet turn on than the tnyswitch and topswitch?...and is therefore better with common mode EMC?
Do all the innoswitchs in the inSOP24D package have the same pinout?
The innoswitch is meant to go under the transformer, but presumably its best if you can get a shielding layer of "quiet node" (non switching node) copper in between the transfoemer and the innoswitch?
Hi treez,
Regarding your first question, just to clarify, are you planning to use a transformer with a different turns ratio while using the InnoSwitch?
The FWD pin on the InnoSwitch family is necessary for the whole flyback operation. At start-up, the primary-side initially switches without any feedback (open loop). When the secondary side control circuit becomes powered by the FWD pin or by the VOUT pin, the secondary side control takes over and is in charge in requesting a switching cycle to the primary(closed loop). This handshake is also done after startup during conditions when the primary switching cycle and the secondary cycle requests do not match.
Disconnecting the FWD pin however prevents the primary-secondary handshake from happening, which causes the primary side to auto restart. The FWD pin is also in charge for the timing information when turning on and off the SR FET on the secondary side.
For your second question, the InnoSwitch3 family datasheets offer the optimal switching frequency where the conduction losses and switching losses are optimized. While recommended, one can choose to decrease or increase the operating switching frequency as long as the thermals and primary inductance and peak current tolerances are considered to prevent the unit to auto restart due to overload protection
For your third question, the primary switch of the InnoSwitch3 is integrated into the IC. Some of its operation (eg. gate drive signal) are not usually observable and the overall specifications are covered by intellectual property. The next best thing is to compare designs using the InnoSwitch to another design using TOPSwitch or TinySwitch.
For your fourth question, different InnoSwitch3 families have different pinout for different applications. Here are the different InnoSwicth3 families with InSOP-24D Packaging and some of their features:
InnoSwitch3-AQ (Automotive applications, up to 100 W operation)
InnoSwitch3-CE (up to 65 W operation)
InnoSwitch3-CP (Constant Power profile feature, up to 100 W operation)
InnoSwitch3-EP (up to 100 W operation)
InnoSwitch3-MX (Paired with InnoMux IC, up to 85 W operation)
InnoSwitch3-PD (Integrated USB Type-C and USB-PD Controller, up to 100 W operation)
InnoSwitch3-Pro (Digitally controllable, up to 100 W operation)
Among these, InnoSwitch3-AQ, -CE, -CP, and -EP have the same pinout. InnoSwitch3-MX, -PD, and -Pro all have different pinouts
This link can provide more information on the different InnoSwitch families: https://www.power.com/products/innoswitch?segment=ac-dc-conversion
For your last question, it is generally not required to place a shielding layer between the transformer and the InnoSwitch IC in terms of control and operation. A shielding layer may be added as long as its effects on EMC are considered (EMI, Surge, ESD).
I have provided the application notes for the design guide for InnoSwitch3. I hope to have helped you with your questions. Feel free to ask again if you have any clarifications. Thanks!