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TC1142 Datasheet(PDF) 7 Page - Microchip Technology |
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TC1142 Datasheet(HTML) 7 Page - Microchip Technology |
7 / 12 page 2002 Microchip Technology Inc. DS21360B-page 7 TC1142 TABLE 3-2: LOW ESR SURFACE-MOUNT CAPACITOR MANUFACTURERS 3.3 Power Efficiency Assuming the output is loaded with at least 20% of the maximum available output current, the power efficiency of the TC1142 can be estimated using the following equation: EQUATION 3-5: For example, a 3.2 Volt VIN, and a -5 Volt VR will have an efficiency of approximately 78%. For loads less than 20% of the maximum available output current, the power efficiency will be substantially reduced. Other factors that affect the actual efficiency include: 1. Losses from power consumed by the internal oscillator (if used). 2. I2R losses due to the on-resistance of the MOSFET charge pump switches. 3. Charge pump capacitor losses due to ESR. 4. Losses that occur during charge transfer (from the flying capacitors to the output capacitor) when a voltage difference exists between these capacitors. 3.4 Choice of -2x or -1x Connections If required output voltage can be achieved using a -1x configuration then this is preferred for the following reasons: 1. Power efficiency is improved from VR/2VIN to VR/VIN 2. Only one flying capacitor needed 3. The output ripple becomes proportional to VIN – VR rather than 2 VIN – VR. 3.5 Layout Considerations Proper layout is important to obtain optimal perfor- mance. Mount capacitors as close to their connecting device pins as possible to minimize stray inductance and capacitance. It is recommended that a large ground plane be used to reduce noise leakage into other circuitry. FIGURE 3-4: TIMING DIAGRAM Manufacturer Type Phone AVX Corp. TPS series surface-mount tantalum X7R type surface-mount ceramic 803-448-9411 Matsuo 267 series surface-mount tantalum X7R type surface-mount ceramic 714-969-2491 Sprague 593D, 594D, 595D series surface-mount tantalum 207-324-4140 Murata Ceramic chip capacitors 800-831-9172 Taiyo Yuden Ceramic chip capacitors 800-348-2496 Tokin Ceramic chip capacitors 408-432-8020 η = |VR| 2(VIN) CCLK VOUT –VR Internal Oscillator Shutdown External Clock Shutdown t0 = counter timeout (~160 µsec) t0 VIL GND VIH t0 |
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Descripción similar - TC1142 |
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