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06-10-2017 07:48 AM
1. The source and sink current of isolated driver of Si827x are 1.8A and 4A respectively, but the fall time is larger than the rising time. This phenomenon is quite different from drivers manufactured by TI, Maxim and so on.
2. The load used to test the rise and fall time of Si827x is only 200pF, while the typical capacitance of MOSFET or GaN are 1nF. Even with 200pF capacitance, the rise and fall time is still larger than the driver of LM5113 from TI whose source and simk current is 1.2A and 5A respectively with load capacitance 1000pF.
Can anybody help to explain this!
Solved! Go to Solution.
06-12-2017 04:23 PM - last edited on 06-12-2017 04:30 PM by Salesforce
Tr and Tf depend on load. Yes we chose 200pF as that was a common load choice for our automatic test system.
As you've noticed TI only specifies this at one point, 1000pF. However, if the load is swept it will give a a more complete picture.
Silicon Labs' driver datasheets generally provide the 1 point guarantee spec like TI. However, we also provide a picture illustrating how the Tr/Tf vary versus load. For instance, see the picture below for the Si823x family. As the plot below shows, either Tr or Tf can be larger depending on load. A similar plot is in our Si827x datasheet. In general this relationship will depend on whether PMOS or NMOS type transistors were used on a given driver's output stage. The exact design details for a driver are usually proprietary.
Si823x (4A, Tr/Tf versus Load)
See Figure 3.18. Rise/Fall Time vs. Supply Voltage in Si823x datasheet.
06-12-2017 10:29 PM
Thanks very much for you comprehansive explanation!
In fact, as you have said that either Tr or Tf can be larger depending on load, driving voltage, driver output stage transistor characteristics and so on. The question is Si827x series driver can be used to drive various power semiconductor device with different gate capacitance at different driving voltage and swiching speed. The Tr/Tf vs load test figure under only one special test conditon can't cover all actual situations as illustrated with Figure2.12 in Si827x datasheet. Maybe it's a problem of Limitation of my knowledge. But I have no idea how to estimate the Tr/Tf time when adopting Si8271 to drive a GaN device with 5V/0V turning on/off voltage with the informaton from the Si827x datasheet.
The driving current may change with the variation of the gate voltage, so the Tr/Tf can only be determined by precise simulation or experiment. I hope that the information of Tr/Tf time of Si827x with 5V voltage and 1000pF capacitance load can be given in the datasheet for the convenience of usage.
06-13-2017 07:28 AM