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HIP6020A Datasheet(PDF) 10 Page - Intersil Corporation |
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HIP6020A Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 16 page 10 OUT2 Voltage Selection The AGP regulator output voltage is internally set to 1.5V or continuously on, based on the status of the SELECT pin. SELECT pin is internally pulled ‘high’, such that left open, the standard buck MOSFET will be continuously on, VOUT2 being equal to the input voltage (3.3V) less any voltage drop across the MOSFET’s rDS(ON) and output inductor’s DCR. The other setting available is 1.5V, which can be obtained by grounding the SELECT pin using a jumper or another suitable method capable of sinking a few tens of microamperes. The status of the SELECT pin cannot be changed during operation of the IC without possibly causing a fault condition. Application Guidelines Soft-Start Interval Initially, the soft-start function clamps the error amplifier’s output of the PWM converters. This generates PHASE pulses of increasing width that charge the output capacitor(s). After the output voltage increases to approximately 70% of the set value, the reference input of the error amplifier is clamped to a voltage proportional to the SS pin voltage. The resulting output voltages start-up as shown in Figure 3. The soft-start function controls the output voltage rate of rise to limit the current surge at start-up. The soft-start interval and the surge current are programmed by the soft-start capacitor, CSS. Programming a faster soft-start interval increases the peak surge current. The peak surge current occurs during the initial output voltage rise to 70% of the set value. Using the recommended 0.1 µF soft start capacitor insures all output voltages ramp up to their set values within 10ms of the input voltages reaching POR levels. Shutdown Neither PWM output switches until the soft-start voltage (VSS) exceeds the oscillator’s valley voltage. Additionally, the reference on each linear’s amplifier is clamped to the soft-start voltage. Holding the SS pin low (with an open drain or open collector signal) turns off all four regulators. Layout Considerations MOSFETs switch very fast and efficiently. The speed with which the current transitions from one device to another causes voltage spikes across the interconnecting impedances and parasitic circuit elements. The voltage spikes can degrade efficiency, radiate noise into the circuit, and lead to device over-voltage stress. Careful component layout and printed circuit design minimizes the voltage spikes in the converter. Consider, as an example, the turn-off transition of the upper MOSFET. Prior to turn-off, the upper MOSFET was carrying the full load current. During the turn- off, current stops flowing in the upper MOSFET and is picked up by the lower MOSFET or Schottky diode. Any inductance in the switched current path generates a large voltage spike during the switching interval. Careful component selection, tight layout of the critical components, and short, wide circuit traces minimize the magnitude of voltage spikes. There are two sets of critical components in a DC-DC converter using a HIP6020A controller. The switching power components are the most critical because they switch large amounts of energy, and as such, they tend to generate equally large amounts of noise. The critical small signal components are those connected to sensitive nodes or those supplying critical bypass current. The power components and the controller IC should be placed first. Locate the input capacitors, especially the high- frequency ceramic de-coupling capacitors, close to the power switches. Locate the output inductor and output capacitors between the MOSFETs and the load. Locate the PWM controller close to the MOSFETs. The critical small signal components include the bypass capacitor for VCC and the soft-start capacitor, CSS. Locate these components close to their connecting pins on the control IC. Minimize any leakage current paths from SS node, since the internal current source is only 28 µA. A multi-layer printed circuit board is recommended. Figure 7 shows the connections of the critical components in the converter. Note that the capacitors CIN and COUT each could represent numerous physical capacitors. Dedicate one solid layer for a ground plane and make all critical component ground connections with vias to this layer. Dedicate another solid layer as a power plane and break this plane into smaller islands of common voltage levels. The power plane should support the input power and output power nodes. Use copper filled polygons on the top and bottom circuit layers for the PHASE nodes, but do not unnecessarily oversize these particular islands. Since the PHASE nodes are subjected to very high dV/dt voltages, the stray capacitor formed between these islands and the surrounding circuitry will tend to couple switching noise. Use the remaining printed circuit layers for small signal wiring. The wiring traces from the control IC to the MOSFET gate and source should be sized to carry 2A peak currents. HIP6020A |
Similar Part No. - HIP6020A_01 |
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Similar Description - HIP6020A_01 |
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