AN42 | APPLICATION NOTE |
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4.Premature shut down can be caused by an inappropriate value of sense resistor. See the Sense Resistor section.
5.A poor load regulation can have many causes. You should first check the voltages and signals at the critical pins.
6.The VREF pin should be at the voltage set by the VID pins. If the power supply pins are correct and the VID pins are correct, the VREF should be at the correct volt- age.
7.Next check the oscillator pin. A saw tooth wave at the frequency set by the external capacitor should be seen.
8.When the VREF and CEXT pins are determined to be correct and the output voltage is still incorrect look at the waveform at VCCQP. This pin should be swinging from ground to +12V (in the +12V application) and from slightly below +5V to about +10V (charge pump application). If the VCCQP pin is noisy, with ripples and overshoots, then the noise may cause the converter to function improperly.
9.Next, look at the HIDRV pin. This pin directly drives the gate of the FET. It should provide a gate drive (Vgs) of about 5V when turning the FET on. A careful study of the layout is recommended. See the PCB Layout Guide- lines and Considerations section.
10.Experience shows that the most frequent errors are using incorrect components, improper connections, and poor layout.
Performance Evaluation
This section shows the results of a random sample evalua- tion. Use these results as a reference guide for evaluating the RC5040
Load Regulation
VID | Iload (A) | Vout (V) |
0100 | 0.5 | 3.0904 |
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| 1.0 | 3.0825 |
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| 2.0 | 3.0786 |
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| 3.0 | 3.0730 |
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| 4.0 | 3.0695 |
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| 5.0 | 3.0693 |
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| 6.0 | 3.0695 |
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| 7.0 | 3.0695 |
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| 8.0 | 3.0694 |
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| 9.0 | 3.0694 |
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| 9.9 | 3.0691 |
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Load Regulation 0.5A – 9.9A | 0.70% | |
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VID | Iload (A) | Vout (V) |
0010 | 0.5 | 3.2805 |
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| 1.0 | 3.2741 |
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| 2.0 | 3.2701 |
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| 3.0 | 3.2642 |
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| 4.0 | 3.2595 |
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| 5.0 | 3.2597 |
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| 6.0 | 3.2606 |
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| 7.0 | 3.2611 |
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| 8.0 | 3.2613 |
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| 9.0 | 3.2611 |
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| 10.0 | 3.2607 |
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| 11.0 | 3.2599 |
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| 12.0 | 3.2596 |
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| 12.4 | 3.2596 |
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Load Regulation 0.5A – 12.4A | 0.64% | |
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