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LM3102

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SNVS515G – SEPTEMBER 2007 – REVISED JANUARY 2012

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The LM3102 can be remotely shutdown by pulling the voltage of the EN pin below 1V. 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 3. Shutdown Implementation

Current Limit

Current limit detection is carried out during the off-time by monitoring the re-circulating current through the

synchronous MOSFET. Referring to the Functional Block Diagram, when the main MOSFET is turned off, the

inductor current flows through the load, the PGND pin and the internal synchronous MOSFET. If this current

exceeds 2.7A, the current limit comparator toggles, and as a result disabling the start of the next on-time period.

The next switching cycle starts when the re-circulating current falls back below 2.7A (and the voltage at the FB

pin is below 0.8V). The inductor current is monitored during the on-time of the synchronous MOSFET. As long as

the inductor current exceeds 2.7A, the main MOSFET will remain inhibited to achieve current limit. The operating

frequency is lower during current limit due to a longer off-time.

Figure 2), the next on-time will not initiate until that the current drops below 2.7A (assume the voltage at the FB

pin is lower than 0.8V). During each on-time the current ramps up an amount equal to:

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Figure 4. Inductor Current - Current Limit Operation

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