Ramp-Time DCDC (LT8652S)

[Pit (Gast)]

Hallo liebes Forum,

Um die "ramp-time" des LT8625S einzustellen, steht im Datenblatt des 
LT8652S folgendes:

SS2 (Pin 2): Channel 2 Output Tracking and Soft-Start
Pin. This pin allows user control of output voltage ramp
rate during start-up. A SS2 voltage below 0.6V forces
the LT8652S to regulate the FB2 pin to equal the SS2 pin
voltage. When SS2 is above 0.6V, the internal reference
resumes control of the error amplifier. An internal 2µA
pull-up current from VCC on this pin allows a capacitor
to program output voltage slew rate. This pin is pulled
to ground with a 200O MOSFET during shutdown and
fault conditions; use a series resistor if driving from a
low impedance output. This pin may be left floating if the
soft-start feature is not being used.

Ich verstehe nicht, wie ich jetzt den benötigten Kondensator für z.B. 
eine ramp-time von 300µs berechne.

Danke für eure Hilfe!

[GuruGuru (Gast)]

>> When SS2 is above 0.6V, the internal reference
resumes control of the error amplifier. An internal 2µA
pull-up current...
delta U = delta Q / C = I * delta t / C => C= I * delta t / delta U
C= 2µA * 300µs (wirklich so klein?? warum nicht ~10ms?) / 0,6V = 1nF

[Pit (Gast)]

Danke!