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ISL6522 Datasheet(PDF) 6 Page - Intersil Corporation |
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ISL6522 Datasheet(HTML) 6 Page - Intersil Corporation |
6 / 15 page 6 FN9030.8 March 10, 2006 OCSET Connect a resistor (ROCSET) from this pin to the drain of the upper MOSFET. ROCSET, an internal 200µA current source (IOCS), and the upper MOSFET on-resistance (rDS(ON)) set the converter overcurrent (OC) trip point according to the following equation: An overcurrent trip cycles the soft-start function. SS Connect a capacitor from this pin to ground. This capacitor, along with an internal 10 µA current source, sets the soft-start interval of the converter. COMP and FB COMP and FB are the available external pins of the error amplifier. The FB pin is the inverting input of the error amplifier and the COMP pin is the error amplifier output. These pins are used to compensate the voltage-control feedback loop of the converter. EN This pin is the open-collector enable pin. Pull this pin below 1V to disable the converter. In shutdown, the soft-start pin is discharged and the UGATE and LGATE pins are held low. GND Signal ground for the IC. All voltage levels are measured with respect to this pin. PHASE Connect the PHASE pin to the upper MOSFET source. This pin is used to monitor the voltage drop across the MOSFET for overcurrent protection. This pin also provides the return path for the upper gate drive. UGATE Connect UGATE to the upper MOSFET gate. This pin provides the gate drive for the upper MOSFET. This pin is also monitored by the adaptive shoot through protection circuitry to determine when the upper MOSFET has turned off. BOOT This pin provides bias voltage to the upper MOSFET driver. A bootstrap circuit may be used to create a BOOT voltage suitable to drive a standard N-Channel MOSFET. PGND This is the power ground connection. Tie the lower MOSFET source to this pin. LGATE Connect LGATE to the lower MOSFET gate. This pin provides the gate drive for the lower MOSFET. This pin is also monitored by the adaptive shoot through protection circuitry to determine when the lower MOSFET has turned off. PVCC Provide a bias supply for the lower gate drive to this pin. VCC Provide a 12V bias supply for the chip to this pin. Functional Description Initialization The ISL6522 automatically initializes upon receipt of power. Special sequencing of the input supplies is not necessary. The Power-On Reset (POR) function continually monitors the input supply voltages and the enable (EN) pin. The POR monitors the bias voltage at the VCC pin and the input voltage (VIN) on the OCSET pin. The level on OCSET is equal to VIN Less a fixed voltage drop (see overcurrent protection). With the EN pin held to VCC, the POR function initiates soft-start operation after both input supply voltages exceed their POR thresholds. For operation with a single +12V power source, VIN and VCC are equivalent and the +12V power source must exceed the rising VCC threshold before POR initiates operation. The POR function inhibits operation with the chip disabled (EN pin low). With both input supplies above their POR thresholds, transitioning the EN pin high initiates a soft-start interval. Soft-Start The POR function initiates the soft-start sequence. An internal 10 µA current source charges an external capacitor (CSS) on the SS pin to 4V. Soft-start clamps the error amplifier output (COMP pin) to the SS pin voltage. Figure 3 shows the soft- start interval. At t1 in Figure 3, the SS and COMP voltages reach the valley of the oscillator’s triangle wave. The oscillator’s triangular waveform is compared to the ramping error amplifier voltage. This generates PHASE pulses of increasing width that charge the output capacitor(s). This interval of increasing pulse width continues to t2, at which point the output is in regulation and the clamp on the COMP pin is released. This method provides a rapid and controlled output voltage rise. IPEAK IOCS ROCSET • rDS ON () -------------------------------------------- = ISL6522 |
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