Shenzhen Mingjiada Electronics Co., Ltd. supplies the TI TPS2553 2.5V to 6.5V 85mΩ high-precision adjustable current-limiting USB power distribution switch.
I. Overview of the TPS2553
The TPS2553 is a high-side N-channel MOSFET-based, high-precision, adjustable current-limiting power distribution switch from TI. It is specifically designed for USB port power supply, high-capacitance loads and short-circuit protection applications. The enable pin is active-high, and it features built-in reverse blocking capability. It operates within a voltage range of 2.5V to 6.5V, with a typical on-resistance of 85 mΩ. It is a classic load switch solution for power channel management in USB hubs and embedded devices.
The TPS2553 enables programmable current-limiting thresholds via a single external resistor connected to the ILIM pin, with a typical current-limiting range of 75 mA to 1.7 A and a maximum continuous load capacity of 1.5 A; In high-current modes, current-limiting accuracy reaches ±6 per cent, meeting the stringent requirements of USB power specifications for port current limiting. It also incorporates soft-start, overcurrent, overtemperature and reverse voltage protection, along with a FAULT output to rapidly signal power supply anomalies.
II. Analysis of the TPS2553’s Core Electrical Parameters
1. Input voltage VIN: 2.5 V to 6.5 V
Covers USB 5 V power supply systems whilst being compatible with 3.3 V auxiliary power supplies, making it suitable for port power distribution in non-5 V power domains such as embedded motherboards, set-top boxes, industrial peripherals and digital televisions.
2. On-resistance Rds(on): Typical 85 mΩ (DBV package)
With a low on-resistance of 85 mΩ, the channel voltage drop is only approximately 85 mV at an output current of 1 A, resulting in a power dissipation of 0.085 W and minimal temperature rise, making it suitable for long-term operation under load; the low internal resistance reduces the voltage drop across the USB port, ensuring a stable supply voltage to peripheral devices.
3. Adjustable current limit range: 75 mA to 1,700 mA (typical)
The current limit point is set via an external precision resistor (RILIM) connected to the ILIM pin; a 1% precision metal-film resistor is sufficient to achieve high-precision current limiting; Current limiting accuracy is typically ±6% at the 1.7A setting and ±7.5% at the 1A setting. Compared to standard USB switches with fixed current limiting, this device offers flexible current limiting settings, allowing thresholds to be customised according to the power specifications of different USB 2.0 and USB 3.x ports.
4. Switching Characteristics
A built-in charge pump drives the N-MOSFET, with controlled rising and falling edges; the soft-start function suppresses inrush current during power-up, making it suitable for high-capacitance output loads; the overcurrent response is typically 2 μs, and in the event of a short circuit, the device rapidly enters constant-current limiting to prevent the upstream power supply from failing.
5. Temperature Range: –40°C to +125°C
With a wide temperature range, it is suitable for both consumer electronics and industrial equipment; the TPS2553-Q1 version is automotive-grade and designed for in-vehicle USB applications.
III. Internal Architecture and Operating Principles of the TPS2553
The TPS2553 integrates a charge pump, a high-side N-MOS power transistor, a current sense loop, an ILIM current-limiting reference, a fault comparator, a thermal protection module and a FAULT open-drain output.
1. Normal On-State Mode
When the EN pin is at a high level, the chip’s internal charge pump raises the MOSFET gate voltage; the N-MOSFET is fully turned on, allowing VIN to pass directly to VOUT. Current flows through the power transistor to supply the load; at this point, the device incurs only 85 mΩ of on-state loss.
2. Constant-Current Limiting Operating Mechanism (TPS2553)
When the load current exceeds the RILIM set threshold, the internal current loop reduces the MOSFET gate voltage, causing the power MOSFET to enter the linear region and maintain a constant output current; it does not switch off immediately. The FAULT pin is pulled low to trigger an alarm. During prolonged constant-current operation, the chip’s power dissipation accumulates continuously; when the junction temperature exceeds the thermal shutdown threshold (typically 135°C), the device shuts down and automatically attempts to resume power supply once the temperature has dropped by approximately 10°C within the hysteresis window.
3. Reverse Voltage Protection (Reverse Blocking)
A built-in reverse voltage comparator ensures that when the VOUT voltage exceeds VIN (e.g. reverse current backflow from a USB peripheral), the chip immediately switches off the power transistor to prevent current from flowing back from the output to the input, thereby protecting the upstream host power supply. This is a critical protective function for USB ports, preventing damage to the host power domain caused by reverse current backflow during hot-swapping.
4. Over-Temperature Protection (OTP)
The chip’s junction temperature is monitored in real time; if the temperature exceeds the threshold, the power switch is shut down immediately. The circuit features thermal hysteresis to prevent frequent oscillation between on and off states.
IV. Brief Description of TPS2553 Pin Functions (DBV SOT23-6 Package)
- VIN: Power supply input
- VOUT: Power supply output; connected to the USB port and output capacitor
- EN: Enable; a high level activates the power channel
- ILIM: Current limit programming pin; an external resistor connected to ground sets the current limit threshold
- FAULT: Open-drain fault output; goes low in the event of overcurrent, reverse voltage or overheating; requires a pull-up resistor
- GND: Signal and power ground
Current-limiting calculation logic: The ILIM pin outputs a reference voltage; the current flowing through RILIM is fed back to the internal loop. The current-limiting threshold is inversely proportional to the resistance of RILIM: the higher the value of RILIM, the lower the current limit; the lower the value of RILIM, the higher the current limit. When designing the circuit, select a 1% precision resistor for this application.
V. Summary of TPS2553 Protection Mechanisms
1. Programmable constant-current limiting protection: Clamps the output current during overload or short-circuit conditions to protect the host power supply; the TPS2553 maintains a constant current, whilst the TPS2553-1 shuts down.
2. Reverse voltage blocking protection: Shuts down when the output voltage exceeds the input voltage to prevent reverse current flow.
3. Thermal shutdown protection (OTP): Shuts down when junction temperature exceeds the threshold, with temperature hysteresis.
4. Soft start: Controllable power-up slope to suppress inrush current in large capacitive loads and reduce input voltage sag.
5. FAULT indication: Open-drain output; the MCU can detect fault conditions and report them to the system.
VI. Typical Application Scenarios for the TPS2553
- USB hubs, USB-A host port power supply switches (the most common application, compliant with USB port current-limiting specifications)
- Power supply channels for set-top boxes, digital televisions and VOIP telephone peripherals
- Power control for pluggable peripherals on embedded motherboards
- Power supply for hot-swappable modules in industrial automation equipment
- Power protection for external interfaces on portable devices
Extended Applications: Can be used for power distribution to USB interfaces on humanoid robot peripherals, providing hot-swap, short-circuit and overcurrent protection for USB peripherals such as robot hands and sensing modules, whilst ensuring stable control of the peripheral power supply path.
VII. TPS2553 Design Key Points and PCB Considerations
1. RILIM Resistor Selection: Prioritise 1% precision metal-film resistors to ensure current-limiting accuracy; position the resistor close to the ILIM pin to minimise trace interference.
2. Capacitor Layout: Place a 0.1μF ceramic decoupling capacitor close to the VIN pin; position the output capacitor at the VOUT terminal—note that a higher capacitance results in a larger inrush current, which must be evaluated in conjunction with soft-start considerations.
3. Power Ground Handling: Keep the VIN/VOUT high-current paths short and wide; connect the power ground to the signal ground at a single point to prevent ground bounce noise from affecting current sampling accuracy.
4. FAULT Pin: Open-drain output; an external pull-up resistor to 3.3V/5V must be connected to enable fault interrupt detection via direct connection to the MCU I/O.
5. Thermal Considerations: Under continuous high-current operation, although the 85 mΩ on-resistance results in low power dissipation, sufficient PCB copper area must be provided to enhance heat dissipation and prevent thermal shutdown.
VIII. Advantages and Limitations of the TPS2553
Advantages
1. High-precision adjustable current limiting with a single-resistor configuration, allowing flexible adaptation to different USB port power levels;
2. Low on-resistance of 85 mΩ, resulting in low voltage drop and high power supply efficiency;
3. Integrated reverse blocking eliminates the need for additional external diodes, simplifying the BOM;
4. Constant-current mode is suitable for prolonged short-circuit testing without instantaneous shutdown; includes fault signal feedback;
5. 2.5 V low-voltage input capability, supporting power distribution to 3.3 V system power domains.
Limitations
1. The TPS2553 operates in constant-current mode; sustained short circuits will cause continuous heating, relying on thermal shutdown protection;
2. Maximum continuous current of 1.5 A; not suitable for high-power USB PD ports exceeding 1.5 A;
3. The high-side N-MOS architecture requires an integrated charge pump, resulting in a slight quiescent current; quiescent power consumption must be assessed for ultra-low-power sleep scenarios.
IX. Summary
The TPS2553 is a high-performance, high-precision, adjustable current-limiting power distribution switch designed for USB ports, featuring a wide input voltage range of 2.5V to 6.5V, a low on-resistance of 85mΩ, and a programmable current limit of 75mA to 1.7A. Combined with comprehensive protection against overcurrent, reverse voltage, overheating and soft-start, as well as a FAULT alarm output, its streamlined BOM and high reliability make it the preferred solution for power protection in USB hosts, hubs and embedded peripheral interfaces.
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