Output Rise time

[daveb377]

Is there a specification for Rise time/Fall time on the +28V for a Noise diode? The +28V supply comes up as the TPS61175 comes up, and there's ~ 70uF of capacitance to charge there. If you're going to automate a Y-Factor measurement like the HP8970, you'll be strobing the noise source on/off to get Thot/Tcold measurements, so slow rise time/fall time will effect the measurements. Something to look at.

[dkozel]

My plan is to automate the noise figure measurements using GNU Radio and general purpose SDRs. I'm assuming that the maximum switching rate will be ~5 Hz with a 50% duty cycle. I haven't been able to find any spec for the rise/fall time for a noise diode.

I'm most concerned about ensuring that no more than 500mA is drawn from the USB 5V source which limits us to ~90mA at 100% efficiency, or more reasonably about 75 mA at 85% efficiency. I'm hoping that the relatively high input capacitance and two layers of soft start will give me enough room to tune the rise time vs inrush current.