d123
Advanced Member level 5
Hi,
I'm trying to understand RDSon a little in this circuit and a difference amplifier output voltage. I suspect that such low RDSon is either my bad maths or a very idealized PMOS model as it doesn't seem to look realistic when I try to understand the datasheet curves and relate them to my VGS and load current.
I think 86mV out of diff amp at 1.64A load is:
50mV min OA output
3mV input offset voltage
16mV PMOS RDSon
16mV PMOS RDSon
= 86mV difference amplifier output.
So, presumably RDSon is 10mOhms per PMOS. With a questionable 27mW per Mosfet PD. I substituted the mosfets for 10mOhm resistors and got the same 11.147V and 1.63A output.
Is that right or wrong reasoning, please?
Also, I can't understand why it's the same 86mV (33mV) for a single and for a back-to-back pair. What might I be misunderstanding or is it something to do with the simulation?
- - - Updated - - -
I've tried to upload both datasheets (FDD4141 and LMC6464) several times but the dismal phone cover here is making it impossible, sorry.
I'm trying to understand RDSon a little in this circuit and a difference amplifier output voltage. I suspect that such low RDSon is either my bad maths or a very idealized PMOS model as it doesn't seem to look realistic when I try to understand the datasheet curves and relate them to my VGS and load current.
I think 86mV out of diff amp at 1.64A load is:
50mV min OA output
3mV input offset voltage
16mV PMOS RDSon
16mV PMOS RDSon
= 86mV difference amplifier output.
So, presumably RDSon is 10mOhms per PMOS. With a questionable 27mW per Mosfet PD. I substituted the mosfets for 10mOhm resistors and got the same 11.147V and 1.63A output.
Is that right or wrong reasoning, please?
Also, I can't understand why it's the same 86mV (33mV) for a single and for a back-to-back pair. What might I be misunderstanding or is it something to do with the simulation?
- - - Updated - - -
I've tried to upload both datasheets (FDD4141 and LMC6464) several times but the dismal phone cover here is making it impossible, sorry.