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TPS62620YFFR Datasheet(PDF) 9 Page - Texas Instruments |
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TPS62620YFFR Datasheet(HTML) 9 Page - Texas Instruments |
9 / 28 page PFMModeatLightLoad PFMRipple PWMModeatHeavyLoad NominalDCOutputVoltage TPS62620, TPS62621, TPS62622 TPS62623, TPS62624, TPS62625 www.ti.com SLVS848D – JULY 2009 – REVISED OCTOBER 2015 Device Functional Modes (continued) When high or low duty cycles are encountered, the loop runs out of range and the conversion frequency falls below 6 MHz. The tendency is for the converter to operate more towards a "constant inductor peak current" rather than a "constant frequency". In addition to this behavior which is observed at high duty cycles, it is also noted at low duty cycles. When the converter is required to operate towards the 6 MHz nominal at extreme duty cycles, the application can be assisted by decreasing the ratio of inductance (L) to the output capacitor's equivalent serial inductance (ESL). This increases the ESL step seen at the main comparator's feed-back input thus decreasing its propagation delay, hence increasing the switching frequency. 8.4.3 Power-Save Mode If the load current decreases, the converter will enter power save mode operation automatically. During power- save mode the converter operates in discontinuous current (DCM) single-pulse PFM mode, which produces low output ripple compared with other PFM architectures. When in power save mode, the converter resumes its operation when the output voltage trips below the nominal voltage. It ramps up the output voltage with a minimum of one pulse and goes into power-save mode when the inductor current has returned to a zero steady state. The PFM on-time varies inversely proportional to the input voltage and proportional to the output voltage giving the regulated switching frequency when in steady-state. PFM mode is left and PWM operation is entered as the output current can no longer be supported in PFM mode. As a consequence, the DC output voltage is typically positioned ca. 0.5% above the nominal output voltage and the transition between PFM and PWM is seamless. Figure 4. Operation in PFM Mode and Transfer to PWM Mode 8.4.4 Output Capacitor Discharge (TPS62624 Only) The TPS62624 device can actively discharge the output capacitor when it turns off. The integrated discharge resistor has a typical resistance of 15 Ω. The required time to discharge the output capacitor at the output node depends on load current and the output capacitance value. All the other voltage options do not have the output capacitor discharge function enabled. 8.4.5 Short-Circuit Protection The TPS6262x devices integrate a P-channel MOSFET current limit to protect the device against heavy load or short circuits. When the current in the P-channel MOSFET reaches its current limit, the P-channel MOSFET is turned off and the N-channel MOSFET is turned on. The regulator continues to limit the current on a cycle-by- cycle basis. As soon as the output voltage falls below ca. 0.4 V, the converter current limit is reduced to half of the nominal value. Because the short-circuit protection is enabled during start-up, the device does not deliver more than half of its nominal current limit until the output voltage exceeds approximately 0.5 V. This needs to be considered when a load acting as a current sink is connected to the output of the converter. Copyright © 2009–2015, Texas Instruments Incorporated Submit Documentation Feedback 9 |
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