analogmosfet
Here is a sentence from Design of Analog CMOS Integrated Circuit that I don't quite understand:
"Note that in contrast to bipolar transistors, a MOS device may be even on if it carries no current."
Could you explain this?
Ron = Vds/Id
If there is no current then Ron is infinity.
How is it possible for the device to be on?
A "contact window" is a loop that connects two materials (usually a metal and a semiconductor) together. Since they are square frames, they look like windows. The picture above is a two-gate mosfet with metal gates. For each of the three source/drains you can clearly see the contact windows, connecting the semiconductor islands to the metal pads. The gates do not need a contact windows in this particular design, as they are already made out of metal.
What leads to lower resistance and capacitance is not so much the contact window itself, but the fact that the signal travels the distance through metal instead of semiconductor.
The BTS50055 is not good for fast PWM. If you look at the data sheet in particular "load switching capabilities and characteristics" on page 3 it tells you how fast the device can switch. Turn on time is somewhere in the 100us range typically and turn off might be about 60us. These numbers need to be 1% or less for decent efficiency and 100us represents 1% of 100Hz. If your switching speed is pretty low then use it.
How can I design a MOSFET H-bridge motor driver controlling only 1 PWM for a motor?
If I understand correctly you have a single PWM signal and you want to drive a H bridge with this signal. I'd start by looking for a couple of beafy N channel mosfets like the IRF1010 and then pick a topside/lowside mosfet driver like LTC4444. Feed PWM to the inputs via a couple of logic gates that create a deadband (so both FETs never switch on at once) and this gives you a half H bridge.
Repeat to make the other half but remember to invert the PWM signal. I'd look to be monitoring current on the dc side of things and forget about the BTS50055.
Best Answer
Take a 10 ohm resistor then measure it, it is 10 ohms. Now disconnect it (no voltage or current applied) do you think it is still 10 ohms ? Or does it have an infinite resistance now that the current is zero ?
In the same way the channel in the MOSFET can be formed when Vgb (the channel is formed by the voltage between Gate and Bulk, the source or drain are not involved in this) is large enough. Then the conductive connection between drain and source is made even when the current is zero.