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ISL6432 Datasheet(PDF) 5 Page - Intersil Corporation |
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ISL6432 Datasheet(HTML) 5 Page - Intersil Corporation |
5 / 12 page 5 Functional Pin Descriptions VCC (Pin 11) Provide a well decoupled 5V bias supply for the IC to this pin. This pin also provides the gate bias charge for the lower MOSFET controlled by the PWM section of the IC, as well as the base current drive for the linear regulators’ external bipolar transistors. The voltage at this pin is monitored for Power-On Reset (POR) purposes. GND (Pin 5) Signal ground for the IC. All voltage levels are measured with respect to this pin. PGND (Pin 9) This is the power ground connection. Tie the synchronous PWM converter’s lower MOSFET source to this pin. BOOT (Pin 7) Connect a suitable capacitor (0.47 µF recommended) from this pin to PHASE. This bootstrap capacitor supplies UGATE driver the energy necessary to turn and hold the upper MOSFET on. OCSET (Pin 12) Connect a resistor from this pin to the drain of the upper PWM MOSFET. This resistor, an internal 40 µA current source (typical), and the upper MOSFET’s on-resistance set the converter overcurrent trip point. An overcurrent trip cycles the soft-start function. The voltage at this pin is monitored for power-on reset (POR) purposes and pulling this pin below 1.25V with an open drain/collector device will shutdown the switching controller. PHASE (Pin 6) Connect the PHASE pin to the PWM converter’s upper MOSFET source. This pin is used to monitor the voltage drop across the upper MOSFET for overcurrent protection. UGATE (Pin 8) Connect UGATE pin to the PWM converter’s upper MOSFET gate. This pin provides the gate drive for the upper MOSFET. LGATE (Pin 10) Connect LGATE to the PWM converter’s lower MOSFET gate. This pin provides the gate drive for the lower MOSFET. COMP and FB (Pins 4, 3) COMP and FB are the available external pins of the PWM converter error amplifier. The FB pin is the inverting input of the error amplifier. Similarly, the COMP pin is the error amplifier output. These pins are used to compensate the voltage-mode control feedback loop of the synchronous PWM converter. DRIVE2, 3, 4 (Pins 1, 15, 13) Connect these pins to the base terminals of external bipolar NPN transistors. These pins provide the base current drive for the regulator pass transistors. FB2, 3, 4 (Pins 2, 16, 14) Connect the output of the corresponding linear regulators to these pins through properly sized resistor dividers. The voltage at these pins is regulated to 0.8V. These pins are also monitored for undervoltage events. Quickly pulling and holding any of these pins above 1.25V (using diode-coupled logic devices) shuts off the respective regulators. Releasing these pins from the pull-up voltage initiates a soft-start sequence on the respective regulator. Description Operation The ISL6432 monitors and precisely controls 4 output voltage levels (Refer to Block and Simplified Power System Diagrams, and Typical Application Schematic). The IC has a synchronous PWM controller and three linear controllers. The PWM controller drives 2 MOSFETs (Q1 and Q2) in a synchronous-rectified buck converter configuration and regulates the output voltage to a level programmed by a resistor divider. The linear controllers are designed to regulate three more of the communication chip set voltages. All linear controllers are designed to employ external NPN bipolar pass transistors. Initialization The ISL6432 automatically initializes upon receipt of input power. Special sequencing of the input supplies is not necessary. The Power-On Reset (POR) function continually monitors the input bias supply voltage. The POR monitors the bias voltage at the VCC pin. The POR function initiates soft-start operation after the bias supply voltage exceeds its POR threshold. Soft-Start The POR function initiates the soft-start sequence. The PWM error amplifier reference input is clamped to a level proportional to the soft-start voltage. As the soft-start voltage slews up, the PWM comparator generates PHASE pulses of increasing width that charge the output capacitor(s). Similarly, all linear regulators’ reference inputs are clamped to a voltage proportional to the soft-start voltage. The ramp- up of the internal soft-start function provides a controlled output voltage rise. Overcurrent Protection All outputs are protected against excessive overcurrents. The PWM controller uses the upper MOSFET’s on-resistance, rDS(ON) to monitor the current for protection against shorted output. All linear controllers monitor their respective FB pins for undervoltage events to protect against excessive currents. A sustained overload (undervoltage on linears or overcurrent on the PWM) on any output results in an independent shutdown of the respective output, followed by subsequent individual re-start attempts performed at an interval equivalent to 3 soft-start intervals. Figure 1 describes the protection feature. At time T0, an overcurrent event sensed across the switching regulator’s upper MOSFET (rDS(ON) sensing) triggers a shutdown of the VOUT1 output. As a result, its internal soft-start initiates a number of soft-start cycles. After a ISL6432 |
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