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TPS61041QDBVRQ1 Fiches technique(PDF) 3 Page - Texas Instruments |
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TPS61041QDBVRQ1 Fiches technique(HTML) 3 Page - Texas Instruments |
3 / 18 page www.ti.com DETAILED DESCRIPTION OPERATION PEAK CURRENT CONTROL I peak(typ) + I LIM ) Vin L 100 ns I peak(typ) + 400 mA ) Vin L 100 ns for the TPS61040 I peak(typ) + 250 mA ) Vin L 100 ns for the TPS61041 (1) SOFTSTART TPS61040-Q1 TPS61041-Q1 SGLS276 – JANUARY 2005 Terminal Functions TERMINAL I/O DESCRIPTION NAME NO. SW 1 I Connect the inductor and the Schottky diode to this pin. This is the switch pin and is connected to the drain of the internal power MOSFET. GND 2 Ground FB 3 I This is the feedback pin of the device. Connect this pin to the external voltage divider to program the desired output voltage. EN 4 I This is the enable pin of the device. Pulling this pin to ground forces the device into shutdown mode reducing the supply current to less than 1 µA. This pin should not be left floating and needs to be terminated. VIN 5 I Supply voltage pin The TPS61040/41 operates with an input voltage range of 1.8 V to 6 V and can generate output voltages up to 28 V. The device operates in a pulse frequency modulation (PFM) scheme with constant peak current control. This control scheme maintains high efficiency over the entire load current range, and with a switching frequency up to 1 MHz, the device enables the use of very small external components. The converter monitors the output voltage, and as soon as the feedback voltage falls below the reference voltage of typically 1.233 V, the internal switch turns on and the current ramps up. The switch turns off as soon as the inductor current reaches the internally set peak current of typically 400 mA (TPS61040) or 250 mA (TPS61041). See the Peak Current Control section for more information. The second criteria that turns off the switch is the maximum on-time of 6 µs (typical). This is just to limit the maximum on-time of the converter to cover for extreme conditions. As the switch is turned off, the external Schottky diode is forward biased delivering the current to the output. The switch remains off for a minimum of 400 ns (typical), or until the feedback voltage drops below the reference voltage again. Using this PFM peak current control scheme, the converter operates in discontinuous conduction mode (DCM) where the switching frequency depends on the output current, which results in high efficiency over the entire load current range. This regulation scheme is inherently stable, allowing a wider selection range for the inductor and output capacitor. The internal switch turns on until the inductor current reaches the typical dc current limit (ILIM) of 400 mA (TPS61040) or 250 mA (TPS61042). Due to the internal propagation delay of typical 100 ns, the actual current exceeds the dc-current limit threshold by a small amount. The typical peak current limit can be calculated: The higher the input voltage and the lower the inductor value, the greater the peak. By selecting the TPS61040 or TPS61041, it is possible to tailor the design to the specific application current limit requirements. A lower current limit supports applications requiring lower output power and allows the use of an inductor with a lower current rating and a smaller form factor. A lower current limit usually has a lower output voltage ripple as well. All inductive step-up converters exhibit high inrush current during start-up if no special precaution is made. This can cause voltage drops at the input rail during start up and may result in an unwanted or early system shut down. 3 |
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