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ISL6530CBZ Datasheet(PDF) 7 Page - Intersil Corporation |
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ISL6530CBZ Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 17 page 7 FN9052.2 November 15, 2004 While the VTT supply “floats”, it is held to about 50% of VDDQ via a low current window regulator which drives VTT via the SENSE2 pin. The window regulator can overcome up to at least ±10mA of leakage on VTT. While V2_SD is high, PGOOD is low. PHASE1 and PHASE2 Connect PHASE1 and PHASE2 to the corresponding upper MOSFET source. This pin is used as part of the upper MOSFET bootstrapped drives. PHASE1 is used to monitor the voltage drop across the upper MOSFET of the VDDQ regulator for over-current protection. The PHASE1 pin is monitored by the adaptive shoot through protection circuitry to determine when the upper FET of the VDDQ supply has turned off. FB1, COMP1, FB2, and COMP2 COMP1, COMP2, FB1, and FB2 are the available external pins of the error amplifiers. The FB1 and FB2 pins are the inverting inputs of each error amplifier and the COMP1 and COMP2 pins are the associated outputs. An appropriate AC network across these pins is used to compensate the voltage-controlled feedback loop of each converter. VREF and VREF_IN VREF produces a voltage equal to one half of the voltage on SENSE1. This low current output is connected to the VREF input of the DDRAM devices being powered. This same voltage is used as the reference input of the VTT error amplifier. Thus VTT is controlled to 50% of VDDQ. VREF_IN is used as an option to overdrive the internal resistor divider network that sets the voltage for both VREF_OUT and the reference voltage for the VTT supply. A 100pF capacitor between VREF_IN and ground is recommended for proper operation. PVCC1 This is the positive supply for the lower gate driver, LGATE1. PVCC1 is connected to a well decoupled 5V. SENSE1 and SENSE2 Both SENSE1 and SENSE2 are connected directly to the regulated outputs of the VDDQ and VTT supplies, respectively. SENSE1 is used as an input to create the voltage at VREF_OUT and the reference voltage for the VTT supply. SENSE2 is used as the regulation point for the window regulator that is enabled in V2_SD mode. Functional Description Overview The ISL6530 contains control and drive circuitry for two synchronous buck PWM voltage regulators. Both regulators utilize 5V bootstrapped output topology to allow use of low cost N-channel MOSFETs. The regulators are driven by 300kHz clocks. The clocks are phase locked and displaced 90o to minimize noise coupling between the controllers. The first regulator includes a precision 0.8V reference and is intended to provide the proper VDDQ to a DDRAM memory system. The VDDQ controller implements overcurrent protection utilizing the rDS(ON) of the upper MOSFET. Following a fault condition, the VDDQ regulator is softstarted via a digital softstart circuit. Included in the ISL6530 is a precision VREF reference output. VREF is a buffered representation of .5xVDDQ. VREF is derived via a precision internal resistor divider connected to the SENSE1 terminal. The second PWM regulator is designed to provide VTT termination for the DDRAM signal lines. The reference to the VTT regulator is VREF. Thus the VTT regulator provides a termination voltage equal to .5xVDDQ. The drain of the upper MOSFET of the VTT supply is connected to the regulated VDDQ voltage. The VTT controller is designed to enable both sinking and sourcing current on the VTT rail. Two benefits result from the ISL6530 dual controller topology. First, as VREF is always .5xVDDQ, the VTT supply will track the VDDQ supply during softstart cycles. Second, the overcurrent protection incorporated into the VDDQ supply will simultaneously protect the VTT supply. Initialization The ISL6530 automatically initializes upon application 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 at the VCC pin. The POR function initiates soft-start operation after the 5V bias supply voltage exceeds its POR threshold. Soft-Start The POR function initiates the digital soft start sequence. The PWM error amplifier reference input for the VDDQ regulator 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). This method provides a rapid and controlled output voltage rise. The soft start sequence typically takes about 7ms. With the VTT regulator reference held at it will automatically track the ramp of the VDDQ softstart, thus enabling a soft-start for VTT. Figure 2 shows the soft-start sequence for a typical application. At t0, the +5V VCC bias voltage starts to ramp. Once the voltage on VCC crosses the POR threshold at time t1, both outputs begin their soft-start sequence. The triangle waveforms from the PWM oscillators are compared to the rising error amplifier output voltage. As the error amplifier voltage increases, the pulse-widths on the UGATE pins increase to reach their steady-state duty cycle at time t2. 1 2 --- V DDQ ⋅ ISL6530 |
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