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ISL6268 Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL6268 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 14 page 9 FN6348.0 August 22, 2006 the PHASE and GND pins is nulled by the voltage dropped across RSEN as ISEN conducts through it. An OCP fault occurs if ISEN rises above the OCP threshold current IOC while attempting to null the negative voltage across the PHASE and GND pins. ISEN must exceed IOC on all the PWM pulses that occur within 20µs. If ISEN falls below IOC on a PWM pulse before 20µs has elapsed, the timer will be reset. An SCP fault will occur within 10µs when ISEN exceeds twice IOC. The relationship between ID and ISEN is written as: The value of RSEN is then written as: where: -RSEN (Ω) is the resistor used to program the overcurrent setpoint -ISEN is the current sense current that is sourced from the ISEN pin -IOC is the ISEN threshold current sourced from the ISEN pin that will activate the OCP circuit -IFL is the maximum continuous DC load current -IPP is the inductor peak-to-peak ripple current -OCSP is the desired overcurrent setpoint expressed as a multiplier relative to IFL Overvoltage Protection When an OVP fault is detected, the PGOOD pin will pull down to 63 Ω and latch-off the converter. The OVP fault will remain latched until the EN pin has been pulled below the falling EN threshold voltage VENTHF or if VCC has decayed below the falling POR threshold voltage VVCC_THF. The OVP fault detection circuit triggers after the voltage across the FB and GND pins has increased above the rising overvoltage threshold VOVR. After the converter has latched-off in response to an OVP fault, the LG gate-driver output will retain the ability to toggle the low-side MOSFET on and off in response to the output voltage transversing the VOVR and VOVF thresholds. Undervoltage Protection When a UVP fault is detected, the PGOOD pin will pull down to 95 Ω and latch-off the converter. The fault will remain latched until the EN pin has been pulled below the falling EN threshold voltage VENTHF or if VCC has decayed below the falling POR threshold voltage VVCC_THF. The UVP fault detection circuit triggers after the voltage across the FB and GND pins has fallen below the undervoltage threshold VUV. Over-Temperature When the temperature of the ISL6268 increases above the rising threshold temperature TOTR, the IC will enter an OTP state that suspends the PWM , forcing the LG and UG gate-driver outputs low. The status of the PGOOD pin does not change nor does the converter latch-off. The PWM remains suspended until the IC temperature falls below the hysteresis temperature TOTHYS at which time normal PWM operation resumes. The OTP state can be reset if the EN pin is pulled below the falling EN threshold voltage VENTHF or if VCC decays below the falling POR threshold voltage V VCC_THF. All other protection circuits function normally during OTP. It is likely that the IC will detect an UVP fault because in the absence of PWM, the output voltage immediately decays below the undervoltage threshold VUV; the PGOOD pin will pull down to 95 Ω and latch-off the converter. The UVP fault will remain latched until the EN pin has been pulled below the falling EN threshold voltage VENTHF or if VCC has decayed below the falling POR threshold voltage VVCC_THF. Programming the Output Voltage When the converter is in regulation there will be 600mV from the FB pin to the GND pin. Connect a two-resistor voltage divider across the VO pin and the GND pin with the output node connected to the FB pin. Scale the voltage-divider network such that the FB pin is 600mV with respect to the GND pin when the converter is regulating at the desired output voltage. The output voltage can be programmed from 600mV to 3.3V. Programming the output voltage is written as: where: -VOUT is the desired output voltage of the converter -VREF is the voltage that the converter regulates to between the FB pin and the GND pin -RTOP is the voltage-programming resistor that connects from the FB pin to the VO pin. In addition to setting the output voltage, this resistor is part of the loop compensation network -RBOTTOM is the voltage-programming resistor that connects from the FB pin to the GND pin Beginning with RTOP between 1kΩ to 5kΩ, calculating RBOTTOM is written as: I SEN RSEN • I D rDS on () • = (EQ. 3) (EQ. 4) R SEN I FL I PP 2 --------- + ⎝⎠ ⎛⎞ OC SP • r DS on () • I OC -------------------------------------------------------------------------- = V REF V OUT R BOTTOM R TOP R BOTTOM + --------------------------------------------------- • = (EQ. 5) R BOTTOM V REF R • TOP V OUT V REF – ------------------------------------- = (EQ. 6) ISL6268 |
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