but i would like to have an rise time and fall time that is very small ...may be 10 -20 nano sesonds...is it easy to achieve with the method you are telling??
Feeding the pulse to the RD network will also affect the risetime. A low impedance resistive divider, e.g. with 50 ohm output resistance, will achieve a better pulse repsonse.To lower the square wave signal, we may add at the output a resistor (say 1K) followed by a rather fast diode (1N4148 low-cost and may work); its anode connected to the resistor and its cathode to ground.
I have a 50% duty cycle PWM signal from the microcontoller with 3.3v and i am using a PMOS as a switch with the resistor between collector to ground to have the desired voltage drop of 1.1v at 40mA current . but i face an offset in the output.
will this type of circuit can make a desired voltage drop at specific current without any offset?
But the maximum current from my MCU is 350mA will this be enough to drive a mosfet.You said that you want 10-20 nano second rising/falling edge, how will you accomplish that speed with a mosfet driven by the mcu PWM with just a few mA?
Even with a very small device having charge of 2nC you will need at least 100mA.
Alex
i need an 1.1v PWM signal as the output with 40ma current .
But the maximum current from my MCU is 350mA will this be enough to drive a mosfet.
You are using an mcu that has an output of 350mA from a single pin?
What is the model you are using?
Alex
This is what has confused me the most. If the output should be 40mA then the load will determine the voltage on it. And the reverse is the same, if the output voltage should be 1.1 V, also the load will determine the current it needs at 1.1V
Edited:
so only R as a load which is equal to 1.1/0.04 Ω can satisfy both.
so when i use this resistance between the drain to ground can i get expected output without any offset?
This was just the first step to the solution.
Do you mean, we can assume from now on that the resistor value is 27.5 Ω ?
This was just the first step to the solution.
Do you mean, we can assume from now on that the resistor value is 27.5 Ω ?
I am using EVK1100 board with AVR32uc3a0512 controller.
Your specification is not correct, the datasheet http://www2.atmel.com/System/Redirect.aspx?dest=/dyn/resources/prod_documents/32058S.pdf
says (page 40) 370mA for all pins, in page 41 you will see that the output high level and output low level current is 4-8mA (max) depending on the pin
Alex
Just to be sure, do you mean by getting an 'offset' voltage that you get a small voltage when MCU is high though in this state the output should be zero?
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