DigiTan
New Member
As part of my battery switchover project, I need to bias a P-Channel MOSFET to go into conduction as one of the power sources drops out. (I'll edit in the schematic when I get back home).
I know that the current in saturation mode is a function of gate-source voltage (Vgs), threshold (Vt), the process transconductance parameter (kp'), and the channel aspect ratio (W/L). So far so good. The problem is: neither kp' nor W/L are specified in the data sheet. [data] I planned on using the datasheet's discreet plots on page 3 to calculate kp' and W/L. The story should go:
kp' (W/L) = 2*Id / (Vgs -Vt)²
...But this is yeilding suspiciously large figures (790mA/V² as opposed to the 1mA/V² range I was expecting). Before I go in monday to verify this manually, I want to check with the forum. The discrete plots are nice, but I really need an equation like this since I want the optimal bias.
Is 790mA/V² a reasonable value for kp'(W/L)?
I know that the current in saturation mode is a function of gate-source voltage (Vgs), threshold (Vt), the process transconductance parameter (kp'), and the channel aspect ratio (W/L). So far so good. The problem is: neither kp' nor W/L are specified in the data sheet. [data] I planned on using the datasheet's discreet plots on page 3 to calculate kp' and W/L. The story should go:
kp' (W/L) = 2*Id / (Vgs -Vt)²
...But this is yeilding suspiciously large figures (790mA/V² as opposed to the 1mA/V² range I was expecting). Before I go in monday to verify this manually, I want to check with the forum. The discrete plots are nice, but I really need an equation like this since I want the optimal bias.
Is 790mA/V² a reasonable value for kp'(W/L)?