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ISL6118HIBZA-T Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL6118HIBZA-T Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 10 page 9 Implementing Autoreset on the ISL6118H Hot Swap Controllers Abstract In applications where the cost, complexity or requirement for a system controller is avoided and an autonomous power control function is desired, a device that can monitor and protect against excessive current failures is needed. This shows how to implement such an autonomous controller using the ISL6118HIB. This application works only with the ‘H’ version of these devices. The ‘H’ version refers to the enable function being asserted upon a high input. Introduction The ISL6118, ISL6119 and ISL6121 are all 2.5V to 5V power supply controllers, each having a different level of current regulation (CR). The ISL6118 and ISL6119 have 2 independent controllers with CR levels of 0.6A and 1.0A respectively whereas the ISL6121 is a single supply controller with a 2A CR level. Each of these devices features integrated power switch(es) for power control. Each switch is driven by a constant current source giving a controlled ramp up of the output voltage. This provides a soft start turn-on eliminating bus voltage drooping caused by in-rush current while charging heavy load capacitances. The independent enabling inputs and fault reporting outputs for each channel are available and necessary for the autonomous autoreset application. The undervoltage (UV) feature prevents turn-on of the outputs unless the ENABLE pin and VIN are >2.5V. During initial turn-on the ISL6118 prevents fault reporting by blanking the fault signal. Rising and falling outputs are current-limited voltage ramps so that both the inrush current and voltage slew rate are limited, independent of load. This reduces supply droop due to surge and eliminates the need for external EMI filters. During operation, once an OC condition is detected the appropriate output is current limited to the appropriate level for 10ms to allow transient conditions to pass. If still in current limit after the current limit period has elapsed, the output is latched off and the fault is reported by pulling the corresponding FAULT low. The FAULT signal is latched low until reset by the ENABLE signal being de- asserted at which time the FAULT signal will clear. It is this described sequence of events that allows for the autoreset function to be implemented in a cost efficient manner requiring the addition of only an RC network per channel to the typical application. Figure 15 illustrates the RC network needed with suggested component values and the configuration of the relevant pins for each autoreset channel. Description of Operation Initially as voltage is applied to VIN, the pull up resistor (Rpu) provides for pull up to VIN on both the ENABLE pin asserting the output once VIN > 2.5V and on the FLTn pin. Once turned on and an overcurrent (OC) condition occurs the IC provides CR protection for 10ms and then the FLTn pin pulls low through Rpu and also pulling the ENABLE low thus resetting the device fault condition. At this time the Rpu charges the cap and the voltage on the ENABLE/FLTn node rises until the ENABLE > 2.0 and the output is asserted on once again. This automatic reset cycle will continue until the OC fault no longer exists on the output. After several seconds in this mode of operation the IC thermal protection invokes adjusting the timing of the on-off cycle to prevent excessive thermal dissipation in the power switch protecting itself and surrounding circuitry. See Figure 16 for operation waveform. . Applications •USB • 2.5V to 5V up to 10W power port protection FIGURE 15. VIN ENABLE FLTn GND ISL6118H Rpu = 2K C = 0.1µF FIGURE 16. AUTO RESET OPERATION IOUT 1A/DIV VOUT 2V/DIV VIN/FLTn 5V/DIV 0A 0V 4ms/DIV ISL6118 |
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