On 26-04-2023 17:38, John Larkin wrote:> On Wed, 26 Apr 2023 14:46:53 +0200, Klaus Vestergaard Kragelund > <klauskvik@hotmail.com> wrote: > >> On 26-04-2023 03:05, John Larkin wrote: >>> On Tue, 25 Apr 2023 17:55:29 -0700, John Larkin >>> <jlarkin@highlandSNIPMEtechnology.com> wrote: >>> >>>> On Tue, 25 Apr 2023 17:24:04 +0200, Klaus Vestergaard Kragelund >>>> <klauskvik@hotmail.com> wrote: >>>> >>>>> On 25-04-2023 16:31, John Larkin wrote: >>>>>> On Tue, 25 Apr 2023 13:31:13 +0200, Klaus Vestergaard Kragelund >>>>>> <klauskvik@hotmail.com> wrote: >>>>>> >>>>>>> Hi >>>>>>> >>>>>>> We have a GaN FET that is dumping voltage into a capacitor. The GaN >>>>>>> drain is connected to 50V, and the capacitor is connected on the source >>>>>>> of the FET. Sort of like this: >>>>>>> >>>>>>> https://www.infineon.com/export/sites/default/_images/product/power/GateDriver/circuit_diagram/Single-High-Side-Driver_Diagram.jpg_1153011823.jpg >>>>>>> >>>>>>> "To load" is connected to a small 50pF capacitor to ground. >>>>>>> >>>>>>> We need to pump current into it very fast for reasons I cannot disclose. >>>>>>> So we turn the high side FET on in about 500ps, and charge the >>>>>>> capacitor. Pretty basic :-) >>>>>> >>>>>> Where do you get a gate driver that can turn on a GaN fet in 500 ps? I >>>>>> need that! A little inductance in series with the gate could help >>>>>> some. The gate resistor will slow things down. >>>>>> >>>>> >>>>> LMG1020 >>>>> >>>>> https://www.ti.com/product/LMG1020 >>>>> >>>>> 2 ohms gate resistor >>>> >>>> Nice part. Do you even need a GaN fet? >>> >>> Shame it's a single 5-volt driver, not one of those bootstrap >>> half-bridge drivers. >>> >>> One might drive a GaN fet half bridge with two of those. One would be >>> grounded, but the other would have to float on the source of the upper >>> fet. Getting power up there would be no big deal, but the logic drive >>> would be interesting. >>> >> >> In our design we use a digital opto to do the levelshift. Downside is >> that the switch node goes to several components so has some capacitance. >> >> One option is to use the LMG1210 which is a high side driver, has a >> little slower switching speed however. > > Nice but slow. >The LMG1020 has 350ps risetime @ 100pF, LMG1210 has 500ps @ 0pF. I don't think the 1210 is significantly slower
Short track and impedance matching
Started by ●April 25, 2023
Reply by ●April 26, 20232023-04-26
