I'm developing a board to drive 5 LED strips with 1A maximum current. I need some help for design validation and component selection. The circuit is the following (repeted 5 times). The PWM signals (5 kHz) come from a PCA9685 or directly from the MCU (I have not decided yet). The MOSFET is a RFD14N05LSM and the driver IC is a MCP1416.
From MOSFET datasheet I calculated the following values. Are they correct? Should I consider some safety factor in the calculations?
- Turn-on current Ig= Qg(5)/t(ON) = 25nC/60ns = 417mA. Qg(5) is the total gate charge at 5V Vgs and t(ON) is the turn-on time from datasheet. For t(on) should I consider the rise time from MCP1416 datasheet, figure 2-1?
- Power dissipation Pds= rds(on)*Ids^2 = 0.1 Ohm * 1A^2 = 100mW. From this, considering a junction to case thermal resistance of 3.125 °C/W, the temperature of the junction should be just 0.3 °C above the ambient temperature.
Regarding the driver circuit:
- Could the following selection values be right for TVS diode D1? Reverse stand-off voltage 5.3V, breakdown voltage 7V, clamping voltage 21V. Should I consider anithing else in the selection of the diode?
- Should I place a resistor between driver IC and the gate? If yes, how can I determine the rigth value and the power dissipation?
- If I don't put the resistor RG, where are eventually dissipated the voltage spikes? I mean, if a 10V peak comes from the driver, the TVS forces the gate to 7V, where are dissipate the other 3V?
- Can I add anything else to this circuit to increase overall reliability?
- The datasheet of the MCP1416, sec. 4.3 (Decoupling Capacitors), recommends putting a low ESR film capacitor for decoupling. Since checking the datasheets of different film capacitors I did not find any reference to the ESR, what can be considered as low ESR? Can I take any film cap?