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LMK212BJ105KGT Datasheet(PDF) 11 Page - Texas Instruments |
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LMK212BJ105KGT Datasheet(HTML) 11 Page - Texas Instruments |
11 / 25 page TPS60111 REGULATED 5V 150mA LOW NOISE CHARGE PUMP DC/DC CONVERTER SLVS216B − JUNE 1999 − JUNE 2008 11 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 detailed description (continued) start-up procedure During start-up, i.e. when ENABLE is set from logic low to logic high, the switches T12 and T14 (charge pump 1), and the switches T22 and T24 (charge pump 2) are conducting to charge up the output capacitor until the output voltage VO reaches 0.8×VIN. When the start-up comparator detects this limit, the IC begins to operate in the mode selected with SKIP and COM. This start-up charging of the output capacitor guarantees a short start-up time and eliminates the need for a Schottky diode between IN and OUT. pulse-skip mode In pulse-skip mode (SKIP = high), the error amplifier disables switching of the power stages when it detects an output higher than 5 V. The oscillator halts. The IC then skips switching cycles until the output voltage drops below 5 V. Then the error amplifier reactivates the oscillator and switching of the power stages starts again. The pulse-skip regulation mode minimizes operating current because it does not switch continuously and deactivates all functions except bandgap reference and error amplifier when the output is higher than 5 V. When switching is disabled from the error amplifier, the load is also isolated from the input. SKIP is a logic input and should not remain floating. The typical operating circuit of the TPS60111 in pulse skip mode is shown in Figure 1. constant-frequency mode When SKIP is low, the charge pump runs continuously at the frequency fOSC. The control circuit, fed from the error amplifier, controls the charge on C1F and C2F by driving the gates of the FETs T12/T13 and T22/T23, respectively. When the output voltage falls, the gate drive increases, resulting in a larger voltage across C1F and C2F. This regulation scheme minimizes output ripple. Since the device switches continuously, the output noise contains well-defined frequency components, and the circuit requires smaller external capacitors for a given output ripple. However, constant-frequency mode, due to higher operating current, is less efficient at light loads than pulse-skip mode. IN IN C1+ C1− ENABLE OUT OUT FB C2+ C2− SYNC SKIP COM CLK PGND GND INPUT 2.7 V to 5.4 V CIN 4.7 µF OUTPUT 5 V 150 mA CO = 33 µF C2F 1 µF C1F 1 µF + OFF/ON TPS60111 + Figure 26. Typical Operating Circuit TPS60111 in Constant Frequency Mode Table 1. Tradeoffs Between Operating Modes FEATURE PULSE-SKIP MODE (SKIP = High) CONSTANT-FREQUENCY MODE (SKIP = Low) Best light-load efficiency X Smallest external component size for a given output ripple X Output ripple amplitude Small amplitude Very small amplitude Output ripple frequency Variable Constant Load regulation Very good Good NOTE: Even in pulse-skip mode the output ripple amplitude is small if the push-pull operating mode is selected via COM. |
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