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TPS60120PWP 데이터시트(PDF) 5 Page - Texas Instruments |
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TPS60120PWP 데이터시트(HTML) 5 Page - Texas Instruments |
5 / 39 page TPS60120, TPS60121, TPS60122, TPS60123, TPS60124, TPS60125 REGULATED 200-mA HIGH EFFICIENCY CHARGE PUMP DC/DC CONVERTERS SLVS257B – NOVEMBER 1999 – REVISED AUGUST 2000 5 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 adaptive mode switching (continued) The voltage on the flying capacitors is measured and compared with the supply voltage (VI). If the voltage across the flying capacitors is smaller than half of the supply voltage, then the charge pump switches into the 1.5x conversion-mode. The charge pump switches back from a 1.5x conversion-mode to a voltage doubler mode if the load current in 1.5x conversion-mode can no longer be delivered. With this control mode the device runs in doubler-mode at low VI and in 1.5x conversion-mode at high VI to optimize the efficiency. The most desirable doubler mode is automatically selected depending on both VI and IL. This means that at light loads the device selects the 1.5x conversion-mode already at smaller supply voltages than at heavy loads. The TPS6012x output voltage is regulated using the ACTIVE-CYCLE regulation. An active cycle controlled charge pump utilizes two methods to control the output voltage. At high load currents it varies the on resistances of the internal switches and keeps the ratio ON/OFF time (=frequency) constant. That means the charge pump runs at a fixed frequency. It also keeps the output voltage ripple as low as in linear-mode. At light loads the internal resistance and also the amount of energy transferred per pulse is fixed and the charge pump regulates the voltage by means of a variable ratio of ON-to-OFF time. In this operating point, it runs like a skip mode controlled charge pump with a very high internal resistance, which also enables a low ripple in this operation mode. Since the charge pump does effectively switch at lower frequencies at light loads, it achieves a low quiescent current. pulse-skip mode In pulse-skip mode the error amplifier disables switching of the power stages when it detects an output higher than the nominal output voltage. The oscillator halts and the IC then skips switching cycles until the output voltage drops below the nominal output voltage. Then the error amplifier reactivates the oscillator and starts switching the power stages again. The pulse-skip regulation mode minimizes operating current because it does not switch continuously and deactivates all functions except bandgap reference, error amplifier, and low-battery/power-good comparator when the output is higher than the nominal output voltage. When switching is disabled from the error amplifier, the load is also isolated from the input. In pulse-skip mode, a special current control circuitry limits the peak current. This assures moderate output voltage ripple and also prevents the device from drawing excessive current spikes out of the battery. start-up procedure During start-up, i.e., when ENABLE is set from logic low to logic high, the output capacitor is charged up with a limited current until the output voltage (VO) reaches 0.8 × VI. When the start-up comparator detects this voltage limit, the IC begins switching. This start-up charging of the output capacitor ensures a short start-up time and eliminates the need of a Schottky diode between IN and OUT. The IC starts into a maximum load resistance of VO(nom)/IO(max). shutdown Driving ENABLE low places the device in shutdown mode. This disables all switches, the oscillator, and control logic. The device typically draws 0.05 µA (1 µA max) of supply current in this mode. Leakage current drawn from the output is as low as 1 µA max. The device exits shutdown once ENABLE is set to a high level. The typical no-load shutdown exit time is 10 µs. When the device is in shutdown, the load is isolated from the input. undervoltage lockout and short-circuit current limit The TPS6012x devices have an undervoltage lockout feature that deactivates the device and places it in shutdown mode when the input voltage falls below the typical threshold voltage of 1.6 V. During a short-circuit condition at the output, the current is limited to 115 mA. |
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