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TPS82085 Fiches technique(PDF) 8 Page - Texas Instruments |
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TPS82085 Fiches technique(HTML) 8 Page - Texas Instruments |
8 / 25 page L V V V V t I 2 f OUT IN OUT IN 2 ON OUT PFM - ´ ´ ´ = TPS82085 SLVSCN4B – OCTOBER 2014 – REVISED AUGUST 2015 www.ti.com Feature Description (continued) (3) In PSM, the output voltage rises slightly above the nominal output voltage in PWM mode. This effect is reduced by increasing the output capacitance. The output voltage accuracy in PSM operation is reflected in the electrical specification table and given for a 22-µF output capacitor. 7.3.2 Low Dropout Operation (100% Duty Cycle) The device offers a low input to output voltage differential by entering 100% duty cycle mode. In this mode, the high-side MOSFET switch is constantly turned on. This is particularly useful in battery powered applications to achieve longest operation time by taking full advantage of the whole battery voltage range. The minimum input voltage to maintain a minimum output voltage is given by: VIN(min) = VOUT(min) + IOUT x RDP (4) Where RDP = Resistance from VIN to VOUT, including high-side FET on-resistance and DC resistance of the inductor. VOUT(min) = Minimum output voltage the load can accept. 7.3.3 Soft Startup The TPS82085 has an internal soft start circuit which ramps up the output voltage to the nominal voltage during a soft start time of typically 0.8ms. This avoids excessive inrush current and creates a smooth output voltage slope. It also prevents excessive voltage drops of primary cells and rechargeable batteries with high internal impedance. The device is able to monotonically start into a pre-biased output capacitor. The device starts with the applied bias voltage and ramps the output voltage to its nominal value. 7.3.4 Switch Current Limit and Short Circuit Protection (Hiccup-Mode) The switch current limit prevents the device from high inductor current and from drawing excessive current from the battery or input voltage rail. Excessive current might occur with a heavy load/shorted output circuit condition. If the inductor peak current reaches the switch current limit, the high-side FET is turned off and the low-side FET is turned on to ramp down the inductor current. Once this switch current limits is triggered 32 times, the devices stop switching and enables the output discharge. The devices then automatically start a new startup after a typical delay time of 66 μs has passed. This is named HICCUP short circuit protection. The devices repeat this mode until the high load condition disappears. 7.3.5 Undervoltage Lockout To avoid mis-operation of the device at low input voltages, an under voltage lockout is implemented, which shuts down the devices at voltages lower than VUVLO with a hysteresis of 200 mV. 7.3.6 Thermal Shutdown The device goes into thermal shutdown and stops switching once the junction temperature exceeds TJSD. Once the device temperature falls below the threshold by 20°C, the device returns to normal operation automatically. 8 Submit Documentation Feedback Copyright © 2014–2015, Texas Instruments Incorporated Product Folder Links: TPS82085 |
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Description similaire - TPS82085 |
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