7.4.1 ON-Time Timer, Shutdown

The ON-time of the LM3102 main MOSFET is determined by the resistor R_ON and the input voltage V_IN. It is calculated as follows:

Equation 5.

The inverse relationship of t_on and V_IN gives a nearly constant frequency as V_IN is varied. R_ON should be selected such that the ON-time at maximum V_IN is greater than 150 ns. The ON-timer has a limiter to ensure a minimum of 150 ns for t_on. This limits the maximum operating frequency, which is governed by Equation 6:

Equation 6.

The LM3102 can be remotely shutdown by pulling the voltage of the EN pin below 1 V. In this shutdown mode, the SS pin is internally grounded, the ON-timer is disabled, and bias currents are reduced. Releasing the EN pin allows normal operation to resume because the EN pin is internally pulled up.

Figure 23. Shutdown Implementation