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TPS51125 Datasheet(PDF) 25 Page - Texas Instruments |
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TPS51125 Datasheet(HTML) 25 Page - Texas Instruments |
25 / 33 page www.ti.com Current Protection 24 9 trip trip trip R ( k ) I ( A ) V ( mV ) ( mV ) m W ´ = - (3) 2 ocp trip dson ripple I V R I = + (4) 1 2 trip IN OUT OUT dson IN V (V V ) V R L f V - ´ = + ´ ´ ´ (5) Over/Under Voltage Protection TPS51125 SLUS786A – OCTOBER 2007 – REVISED NOVEMBER 2007 TPS51125 has cycle-by-cycle over current limiting control. The inductor current is monitored during the ‘OFF’ state and the controller keeps the ‘OFF’ state during the inductor current is larger than the over current trip level. In order to provide both good accuracy and cost effective solution, TPS51125 supports temperature compensated MOSFET RDS(on) sensing. ENTRIPx pin should be connected to GND through the trip voltage setting resistor, RTRIP. ENTRIPx terminal sources ITRIP current, which is 10 µA typically at room temperature, and the trip level is set to the OCL trip voltage VTRIP as below. Note that the VTRIP is limited up to about 205 mV internally. The inductor current is monitored by the voltage between GND pin and LLx pin so that LLx pin should be connected to the drain terminal of the bottom MOSFET properly. Itrip has 4500 ppm/ °C temperature slope to compensate the temperature dependency of the RDS(on). GND is used as the positive current sensing node so that GND should be connected to the proper current sensing device, i.e. the source terminal of the bottom MOSFET. As the comparison is done during the ‘OFF’ state, VTRIP sets valley level of the inductor current. Thus, the load current at over current threshold, IOCP, can be calculated as follows; In an over current condition, the current to the load exceeds the current to the output capacitor thus the output voltage tends to fall down. Eventually, it ends up with crossing the under voltage protection threshold and shutdown both channels. TPS51125 monitors a resistor divided feedback voltage to detect over and under voltage. When the feedback voltage becomes higher than 115% of the target voltage, the OVP comparator output goes high and the circuit latches as the top MOSFET driver OFF and the bottom MOSFET driver ON. Also, TPS51125 monitors VOx voltage directly and if it becomes greater than 5.75 V the TPS51125 turns off the top MOSFET driver. When the feedback voltage becomes lower than 60% of the target voltage, the UVP comparator output goes high and an internal UVP delay counter begins counting. After 32 µs, TPS51125 latches OFF both top and bottom MOSFETs drivers, and shut off both drivers of another channel. This function is enabled after 2 ms following ENTRIPx has become high. Copyright © 2007, Texas Instruments Incorporated Submit Documentation Feedback 25 Product Folder Link(s): TPS51125 |
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