MOSFET DRIVER PROBLEM
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From: Digvijay on 29 Jun 2010 15:47 Hi, I am using TC4427 to drive the MOSFET.. I am giving the signal of 3MHZ with the voltage level of 3.3v.. I have 3 volt at Vdd pin and -8v at the GND pin so my output should be swing between 3v to -8 volt.. i am getting approximate out but not required one.. and also i am not getting 50% duty cycle.. so can anybody tell me what should be the problem.. --------------------------------------- Posted through http://www.EmbeddedRelated.com
From: Jon Kirwan on 29 Jun 2010 16:18 On Tue, 29 Jun 2010 14:47:31 -0500, "Digvijay" <mahidadigvijay(a)n_o_s_p_a_m.gmail.com> wrote: > I am using TC4427 to drive the MOSFET.. I am giving the signal of 3MHZ >with the voltage level of 3.3v.. I have 3 volt at Vdd pin and -8v at the >GND pin so my output should be swing between 3v to -8 volt.. i am getting >approximate out but not required one.. and also i am not getting 50% duty >cycle.. so can anybody tell me what should be the problem.. I don't know anything about the TC4427, but I see from a web page that the output is spec'd at 10 ohms, high and low. If the Qg for your mosfet (you don't say which it is and I cannot look it up) is say 50nC and the dV is 3.3V and let's say that Rg is 2 ohms plus this 10 ohms from the TC4427 for 12 ohms total, then the switching time is: R*(dQ/dV) (This comes from the obvious RC time constant, with C=dQ/dV.) Which is 12 Ohms * 50nC / 3.3V, or almost 200ns. This may be something to consider carefully. Jon
From: Ian Shef on 29 Jun 2010 16:59 "Digvijay" <mahidadigvijay(a)n_o_s_p_a_m.gmail.com> wrote in news:D9WdnaHVToBO0LfRnZ2dnUVZ_qednZ2d(a)giganews.com: > Hi, > I am using TC4427 to drive the MOSFET.. I am giving the signal of 3MHZ > with the voltage level of 3.3v.. Relative to what? The GND pin of the TC4427, or relative to your 0 volt point? The TC4427 needs a low input of 0.8 volts (or less), and a high input of 2.4 volts (or more), RELATIVE TO ITS OWN GND PIN. Are you describing a square wave? A sine wave? More details regarding pulse width, maximum voltage, minimum voltage, etc. please. > I have 3 volt at Vdd pin and -8v at the > GND pin so my output should be swing between 3v to -8 volt.. i am getting > approximate out but not required one.. What does this mean? What are you getting out? Details, please. > and also i am not getting 50% duty > cycle.. so can anybody tell me what should be the problem.. > > > > --------------------------------------- > Posted through http://www.EmbeddedRelated.com
From: Didi on 29 Jun 2010 19:36 On Jun 29, 10:47 pm, "Digvijay" <mahidadigvijay(a)n_o_s_p_a_m.gmail.com> wrote: > Hi, > I am using TC4427 to drive the MOSFET.. I am giving the signal of 3MHZ > with the voltage level of 3.3v.. I have 3 volt at Vdd pin and -8v at the > GND pin so my output should be swing between 3v to -8 volt.. i am getting > approximate out but not required one.. and also i am not getting 50% duty > cycle.. so can anybody tell me what should be the problem.. > > --------------------------------------- > Posted throughhttp://www.EmbeddedRelated.com Quite recently I had some experience with TC4426 from Microchip. They just did not work anywhere near their specs driving the gate of a plain old IRF540. They are usable driving smaller FETs (dual SO-8), but one can see they are close even with these. Did not measure all the details, my feeling is that above 1nF gate capacitance they simply don't work and at 1.5 I know they don't. Just ignore their graphs with rise times up to a few nF, they are totally disconnected from reality. Apparently they have a more lax attitude when it comes to specs at Microchip. Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
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