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TPS2557DRBT Datasheet(PDF) 9 Page - Texas Instruments |
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TPS2557DRBT Datasheet(HTML) 9 Page - Texas Instruments |
9 / 23 page 0 VIN-VOUT-mV 0 20 60 100 140 3.0 0.5 1.0 1.5 2.0 2.5 T =125°C J T =-40°C J T =25°C J 160 R =24.9k ILIM 40 80 120 5.0 4.5 4.0 3.5 TPS2556 TPS2557 www.ti.com SLVS931A – NOVEMBER 2009 – REVISED FEBRUARY 2012 TYPICAL CHARACTERISTICS (continued) Figure 18. Switch Current vs. Drain-Source Voltage Across Switch DETAILED DESCRIPTION OVERVIEW The TPS2556/57 is a current-limited, power-distribution switch using N-channel MOSFETs for applications where short circuits or heavy capacitive loads will be encountered. This device allows the user to program the current-limit threshold between 500 mA and 5.0 A (typ) via an external resistor. This device incorporates an internal charge pump and the gate drive circuitry necessary to drive the N-channel MOSFET. The charge pump supplies power to the driver circuit and provides the necessary voltage to pull the gate of the MOSFET above the source. The charge pump operates from input voltages as low as 2.5 V and requires little supply current. The driver controls the gate voltage of the power switch. The driver incorporates circuitry that controls the rise and fall times of the output voltage to limit large current and voltage surges and provides built-in soft-start functionality. The TPS2556/57 family limits the output current to the programmed current-limit threshold IOS during an overcurrent or short-circuit event by reducing the charge pump voltage driving the N-channel MOSFET and operating it in the linear range of operation. The result of limiting the output current to IOS reduces the output voltage at OUT because N-channel MOSFET is no longer fully enhanced. OVERCURRENT CONDITIONS The TPS2556/57 responds to overcurrent conditions by limiting their output current to IOS . When an overcurrent condition is detected, the device maintains a constant output current and the output voltage reduces accordingly. Two possible overload conditions can occur. The first condition is when a short circuit or partial short circuit is present when the device is powered-up or enabled. The output voltage is held near zero potential with respect to ground and the TPS2556/57 ramps the output current to IOS. The TPS2556/57 will limit the current to IOS until the overload condition is removed or the device begins to thermal cycle. The second condition is when a short circuit, partial short circuit, or transient overload occurs while the device is enabled and powered on. The device responds to the overcurrent condition within time tIOS (see Figure 3). The current-sense amplifier is overdriven during this time and momentarily disables the internal N-channel MOSFET. The current-sense amplifier recovers and ramps the output current to IOS. Similar to the previous case, the TPS2556/57 will limit the current to IOS until the overload condition is removed or the device begins to thermal cycle. The TPS2556/57 thermal cycles if an overload condition is present long enough to activate thermal limiting in any of the above cases. The device turns off when the junction temperature exceeds 135 °C (min) while in current limit. The device remains off until the junction temperature cools 20 °C (typ) and then restarts. The TPS2556/57 cycles on/off until the overload is removed (see Figure 10) . Copyright © 2009–2012, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Link(s): TPS2556 TPS2557 |
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