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HIP6004D Datasheet(PDF) 7 Page - Intersil Corporation |
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HIP6004D Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 14 page 7 FN4855.3 July 13, 2005 Over-Current Protection The over-current function protects the converter from a shorted output by using the upper MOSFET’s on-resistance, rDS(ON) to monitor the current. This method enhances the converter’s efficiency and reduces cost by eliminating a current sensing resistor. The over-current function cycles the soft-start function in a hiccup mode to provide fault protection. A resistor (ROCSET) programs the over-current trip level. An internal 200 μA current sink develops a voltage across ROCSET that is referenced to VIN. When the voltage across the upper MOSFET (also referenced to VIN) exceeds the voltage across ROCSET, the over-current function initiates a soft-start sequence. The soft- start function discharges CSS with a 10μA current sink and inhibits PWM operation. The soft-start function recharges CSS, and PWM operation resumes with the error amplifier clamped to the SS voltage. Should an overload occur while recharging CSS, the soft start function inhibits PWM operation while fully charging CSS to 4V to complete its cycle. Figure 4 shows this operation with an overload condition. Note that the inductor current increases to over 15A during the CSS charging interval and causes an over-current trip. The converter dissipates very little power with this method. The measured input power for the conditions of Figure 4 is 2.5W. The over-current function will trip at a peak inductor current (IPEAK) determined by: where IOCSET is the internal OCSET current source (200μA typical). The OC trip point varies mainly due to the MOSFET’s rDS(ON) variations. To avoid over-current tripping in the normal operating load range, find the ROCSET resistor from the equation above with: 1. The maximum rDS(ON) at the highest junction temperature. 2. The minimum IOCSET from the specification table. 3. Determine IPEAK for , where ΔI is the output inductor ripple current. For an equation for the ripple current see the section under component guidelines titled ‘Output Inductor Selection’. A small ceramic capacitor should be placed in parallel with ROCSET to smooth the voltage across ROCSET in the presence of switching noise on the input voltage. Output Voltage Program The output voltage of a HIP6004D converter is programmed to discrete levels between 1.100VDC and 1.850VDC. The voltage identification (VID) pins program an internal voltage reference (DACOUT) with a TTL-compatible 5-bit digital-to- analog converter (DAC). The level of DACOUT also sets the PGOOD and OVP thresholds. Table 1 specifies the DACOUT voltage for the 32 different combinations of connections on the VID pins. The output voltage should not be adjusted while the converter is delivering power. Remove input power before changing the output voltage. Adjusting the output voltage during operation could toggle the PGOOD signal and exercise the overvoltage protection. ‘11111’ VID pin combination resulting in a 0V output setting activates the Power-On Reset function and disables the gate drives circuitry. For this specific VID combination, though, PGOOD asserts a high level. This unusual behavior has been implemented in order to allow for operation in dual- microprocessor systems where AND-ing of the PGOOD signals from two individual power converters is implemented. Application Guidelines Layout Considerations As in any high frequency switching converter, layout is very important. Switching current from one power device to another can generate voltage transients across the impedances of the interconnecting bond wires and circuit traces. These interconnecting impedances should be minimized by using wide, short printed circuit traces. The critical components should be located as close together as possible, using ground plane construction or single point grounding. 0A 0V TIME (20ms/DIV) 5A 10A 15A 2V 4V FIGURE 4. OVER-CURRENT OPERATION IPEAK IOCSET x ROCSET rDS ON () ----------------------------------------------------- = IPEAK IOUT MAX () ΔI () 2 ⁄ + > HIP6004D |
Similar Part No. - HIP6004D_05 |
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Similar Description - HIP6004D_05 |
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