JAJSAH6H January 2006 – October 2017 LM3100
PRODUCTION DATA.
Current limit detection occurs during the off-time by monitoring the re-circulating current through the low-side synchronous switch. Referring to Functional Block Diagram, when the buck switch is turned off, inductor current flows through the load, into PGND, and through the internal low-side synchronous switch. If that current exceeds 1.9 A the current limit comparator toggles, forcing a delay to the start of the next on-time period. The next cycle starts when the re-circulating current falls back below 1.9 A and the voltage at FB is below 0.8 V. The inductor current is monitored during the low-side switch on-time. As long as the overload condition persists and the inductor current exceeds 1.9 A, the high-side switch will remain inhibited. The operating frequency is lower during an over-current due to longer than normal off-times.
Figure 20 illustrates an inductor current waveform, the average inductor current is equal to the output current, IOUT in steady state. When an overload occurs, the inductor current will increase until it exceeds the current limit threshold, 1.9 A. Then the control keeps the high-side switch off until the inductor current ramps down below 1.9 A. Within each on-time period, the current ramps up an amount equal to:
During this time the LM3100 is in a constant current mode, with an average load current (IOCL) equal to 1.9 A +ΔI/2.