TPS2553DBVT

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1. Describe

The TPS2553DBVT and TPS255x-1 power distribution switches are suitable for applications requiring precise current limiting or experiencing heavy capacitive loads and short circuits, delivering up to 1.5A of continuous load current. These devices offer programmable current-limit thresholds between 75 mA and 1.7 A (typ) through an external resistor. At higher current limit settings, up to ±6% current limit accuracy can be achieved. Controls the rise and fall times of the power switch to minimize current surges during turn-on and turn-off. The TPS2553DBVT device limits the output current to a safe level by using constant current mode when the output load exceeds the current limit threshold. The TPS255x-1 devices provide circuit breaker functionality by latching the power switch during overcurrent or reverse voltage conditions. When the output voltage is higher than the input voltage, an internal reverse voltage comparator disables the power switch to protect the device on the input side of the switch. During overcurrent and reverse voltage conditions, the FAULT output is asserted low. The TPS2553DBVT and TPS255x-1 are current-limited power distribution switches using N-channel MOSFETs for applications experiencing short circuits or large capacitive loads, delivering up to 1.5A of continuous load current. These devices allow the user to program the current-limit threshold between 75 mA and 1.7 A (typ) through an external resistor. Other device shutdown features include thermal protection and reverse voltage protection. The device contains the internal charge pump and gate drive circuitry required to drive N-channel MOSFETs. The charge pump powers the driver circuit and provides the necessary voltage to pull the gate of the MOSFET above the source. The charge pump operates with input voltages as low as 2.5 V and requires very little supply current. The driver controls the gate voltage of the power switch. The driver contains circuitry to control the output voltage rise and fall times to limit high current and voltage surges, and provides built-in soft-start capability. There are two device families that handle overcurrent conditions differently. The TPS255x series enters constant current mode, while the TPS255x-1 series locks when the load exceeds the current limit threshold.

2. Feature

    1. Up to 1.5A maximum load current

    2. ±6% current limit accuracy, 1.7 A (typ)

    3. Complies with USB current limit requirements

    4. Backward compatible with TPS2550 and TPS2551

    5. Adjustable current limit: 75 mA to 1700 mA (typ)

    6. Constant current (TPS255x) and latching (TPS255x-1) versions

    7. Fast Overcurrent Response - 2 µs (typ)

    8. 85mΩ high-side MOSFET (DBV package)

    9. Reverse input and output voltage protection

  10. Operating range: 2.5 V to 6.5 V

  11. Built-in soft start

  12. 15kV ESD protection per IEC 61000-4-2 (with external capacitors)

  13. UL Listed – File No. E169910 and NEMKO IEC60950-1-am1 ed2.0

  14. View TI's switch portfolio

3. Application

    1. USB ports and hubs

    2. Digital Television

    3. Set-top box

    4. VOIP calls

4. Pin configuration

5. Pin Description

6. Function Description

    1. overcurrent condition

        When an overcurrent condition is detected, the device maintains a constant output current and reduces the output voltage accordingly. Two possible overload situations can occur. The first is a short or partial short when the device is powered up or enabled. The output voltage is held near zero potential with respect to ground, and the TPS255x ramps the output current to IOS. The TPS2553DBVT device limits current to the IOS until the overload condition is removed or the device begins thermal cycling. The TPS255x-1 devices limit the current to IOS until the overload condition is removed or the internal deglitch time (7.5 ms typical) is reached and the device shuts down. The device will remain off until power is cycled or the device is turned on. The second is a short circuit, partial short circuit, or transient overload when the device is enabled and powered up. The device responds to an overcurrent condition within time tIOS. The current-sense amplifier is overdriven during this period and temporarily disables the internal current-limiting MOSFET. The current sense amplifier recovers and limits the output current to the IOS. Similar to the previous case, the TPS2553DBVT limits the current to IOS until the overload condition is removed or the device begins thermal cycling; the TPS255x-1 limits the current to IOS until the overload condition is removed or the internal deglitch time is reached and the device is locked. The TPS255x thermally cycles if the overload condition exists long enough to activate thermal limit under any of the above conditions. When the junction temperature exceeds 135°C (typ) and is in current limit, the device will shut down. The device remains off until the junction temperature cools by 10°C (typ), then restarts. The TPS255x cycles on and off until the overload is removed.

    2. Reverse voltage protection

        The reverse voltage protection function is turned off the N-channel MOSFET whenever the output voltage exceeds the input voltage by 135 mV (typical) for 4-ms (typical). A reverse current of (VOUT – VIN)/rDS(on)) are present when this occurs. This prevents damage to devices on the input side of the TPS2553DBVT and TPS2552-1/TPS2253-1 by preventing significant current from sinking into the input capacitance. The TPS2553DBVT devices allow the N-channel MOSFET to turn on once the output voltage goes below the input voltage for the same 4-ms deglitch time. The TPS255x-1 devices keep the device turned off even if the reverse-voltage condition is removed and do not allow the N-channel MOSFET to turn on until power is cycled or the device enable is toggled . The reverse-voltage comparator also asserts the FAULT output (active-low) after 4-ms.

    3. Thermal Sense

        The TPS2553DBVT and TPS255x-1 have self-protection features using two independent thermal-sensing circuits that monitor the operating temperature of the power switch and disable operation if the temperature exceeds recommended operating conditions. The TPS2553DBVT device operates in constant-current mode during an overcurrent conditions, which increases the voltage drop across power-switch. The power dissipation in the package is proportional to the voltage drop across the power switch, which increases the junction temperature during an overcurrent condition. The first thermal sensor turns off the power switch when the die temperature exceeds 135°C (minimum) and the part is in current limit. Hysteresis is built into the thermal sensor, and the switch turns on after the device has cooled approximately 10°C. The TPS2553DBVT and TPS255x-1 also have a second ambient thermal sensor. The ambient thermal sensor turns off the power-switch when the die temperature exceeds 155°C (minimum) regardless of whether the power switch is in current limit and turns on the power switch after the device has cooled approximately 10°C. The TPS255x and TPS255x-1 families continue to cycle off and on until the fault is removed. The open-drain fault reporting output FAULT is asserted (active low) immediately during an overtemperature shutdown condition.

7. Application Information

Both the constant-current devices TPS2553DBVT and latch-off devices operate identically during normal operation, that is, the load current is less than the current-limit threshold and the devices are not limiting current. During normal operation the N-channel MOSFET is fully enhanced, and VOUT = VIN - (IOUT x rDS(on)). The voltage drop across the MOSFET is relatively small compared to VIN, and VOUT ≉ VIN. Both the constant-current devices (TPS255x ) and latch-off devices (TPS255x-1) operate identically during the initial onset of an overcurrent event. Both devices limit current to the programmed current-limit threshold set to RILIM by operating the N-channel MOSFET in the linear mode. During current- limit operation, the N-channel MOSFET is no longer fully-enhanced and the resistance of the device increases. This allows the device to effectively regulate the current to the current-limit threshold. The effect of increasing the resistance of the MOSFET is that the voltage drop a cross the device is no longer negligible (VIN ≠ VOUT), and VOUT decreases. The amount that VOUT decreases is proportional to the magnitude of the overload condition. The expected VOUT can be calculated by, while both the constant-current devices (TPS255x ) and latch-off devices (TPS255x-1) operate identically during the initial onset of an overcurrent event, they behave differently if the overcurrent event lasts longer than the internal delay de-glitch circuit (7.5-ms typical). The constant-current devices (TPS255x ) assert the FAULT flag after the deglitch period and continue to regulate the current to the current-limit threshold indefinitely. In practical circuits, the power dissipation in the package increases the die temperature above the overtemperature shutdown threshold (135°C minimum) , and the device turns off until the die temperature decreases by the hysteresis of the thermal shutdown circuit (10°C typical). The device turns on and continues to thermal cycle until the overloa d condition is removed. The constant-current devices resume normal operation once the overload condition is removed. The latch-off devices (TPS255x-1) assert the FAULT flag after the deglitch period and immediately turn off the device. The device remains off regardless of whether the overload condition is removed from the output. The latch-off devices remain off and do not resume normal operation until the surrounding system either toggles the enable or cycles power to the device.