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ISL6532CCRZ-T Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL6532CCRZ-T Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 16 page 10 Had the cause of the over current still been present after the delay interval, the over current condition would be sensed and the regulator would be shut down again for another delay interval of three soft start cycles. The resulting hiccup mode style of protection would continue to repeat indefinitely. The over-current function will trip at a peak inductor current (IPEAK) determined by: where IOCSET is the internal OCSET current source (20µA typical). The OC trip point varies mainly due to the MOSFET rDS(ON) variations. To avoid over-current tripping in the normal operating load range, find the ROCSET resistor from the equation above with: 1. The maximum rDS(ON) at the highest junction temperature. 2. The minimum IOCSET from the specification table. 3. Determine IPEAK for: , where ∆I is the output inductor ripple current. For an equation for the ripple current see the section under component guidelines titled ‘Output Inductor Selection’. A small ceramic capacitor should be placed in parallel with ROCSET to smooth the voltage across ROCSET in the presence of switching noise on the input voltage. VTT Over Current Protection The internal VTT LDO is protected from fault conditions through a 3.3A current limit. This current limit protects the ISL6532C if the LDO is sinking or sourcing current. During an overcurrent event on the VTT LDO, only the VTT LDO is disabled. Once the over current condition on the VTT rail is removed, VTT will recover. Over/Under Voltage Protection All three regulators are protected from faults through internal Over/Under voltage detection circuitry. If the any rail falls below 85% of the targeted voltage, then an undervoltage event is tripped. An under voltage will disable all three regulators for a period of 3 soft-start cycles, after which a normal soft-start is initiated. If the output is still under 85% of target, the regulators will continue to be disabled and soft- started in a hiccup mode until the fault is cleared. This protection feature works much the same as the VDDQ PWM over current protection works. See Figure 3. If the any rail exceeds 115% of the targeted voltage, then all three outputs are immediately disabled. The ISL6532C will not re-enable the outputs until either the bias voltage is toggled in order to initiate a POR or the S5 signal is forced LOW and then back to HIGH. Thermal Protection (S0/S3 State) If the ISL6532C IC junction temperature reaches a nominal temperature of 140oC, all regulators will be disabled. The ISL6532C will not re-enable the outputs until the junction temperature drops below 110oC and either the bias voltage is toggled in order to initiate a POR or the SLP_S5 signal is forced LOW and then back to HIGH. Shoot-Through Protection A shoot-through condition occurs when both the upper and lower MOSFETs are turned on simultaneously, effectively shorting the input voltage to ground. To protect from a shoot- through condition, the ISL6532C incorporates specialized circuitry which insures that complementary MOSFETs are not ON simultaneously. The adaptive shoot-through protection utilized by the VDDQ regulator looks at the lower gate drive pin, LGATE, and the upper gate drive pin, UGATE, to determine whether a MOSFET is ON or OFF. If the voltage from UGATE or from LGATE to GND is less than 0.8V, then the respective MOSFET is defined as being OFF and the other MOSFET is allowed to turned ON. This method allows the VDDQ regulator to both source and sink current. Since the voltage of the MOSFET gates are being measured to determine the state of the MOSFET, the designer is encouraged to consider the repercussions of introducing external components between the gate drivers and their respective MOSFET gates before actually implementing such measures. Doing so may interfere with the shoot- through protection. TIME T1 T0 T2 500mV/DIV VDDQ VAGP VTT FIGURE 3. VDDQ and VTT OVER CURRENT PROTECTION AND VTT/VAGP LDO UNDER VOLTAGE PROTECTION RESPONSES INTERNAL SOFT-START FUNCTION DELAY INTERVAL IPEAK IOCSET x ROCSET rDS ON () ----------------------------------------------------- = IPEAK IOUT MAX () ∆I () 2 ---------- + > ISL6532C |
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