TPS22810DBVR

The TPS22810DBVR from Texas Instruments is a single-channel load switch with an integrated N-channel MOSFET, adjustable rise time, and quick output discharge in a compact 6-pin SOT-23 package. It is designed for power rail switching applications where controlled turn-on, controlled turn-off, and input voltage monitoring are required.

The device addresses three critical challenges in power distribution design: inrush current management, output discharge control, and undervoltage protection. These features are essential in systems with large capacitive loads, power sequencing requirements, and input voltage monitoring needs.

The adjustable rise time feature, controlled by an external capacitor on the CT pin, allows the designer to set the output voltage ramp rate to any desired value. Without slew rate control, turning on a load switch into a large capacitive load causes a brief but large inrush current as the output capacitor charges. This inrush current can cause the input supply voltage to droop, potentially resetting other devices on the same supply rail. By slowing the turn-on ramp, the TPS22810 limits the inrush current to a manageable level, eliminating supply droop. The CT pin can be left floating for the default fastest rise time, or a capacitor to GND can be added to increase the rise time proportionally.

The quick output discharge (QOD) feature ensures that the output voltage decays in a controlled manner when the switch is turned off. Without QOD, the output voltage would float and decay slowly through the load, potentially leaving downstream circuitry in an undefined state for an extended period. The QOD pin connects an internal pull-down resistor (RPD) between VOUT and GND when the switch is disabled, actively discharging the output capacitor. The QOD can be configured in three ways: (1) connecting an external resistor between VOUT and QOD for a specific discharge rate; (2) shorting QOD to VOUT to use the internal RPD value; or (3) leaving QOD floating to disable the discharge function entirely. The adjustable QOD allows the designer to control the power-down sequencing of the system, even when the system power supply is unexpectedly removed.

The EN/UVLO pin serves a dual function: it acts as the active-high enable input for the switch, and it allows an external resistor divider to set a programmable undervoltage lockout (UVLO) threshold. When the voltage on EN/UVLO falls below the falling threshold (approximately 1.13V), the switch turns off, disconnecting the load from the input. When the voltage rises above the rising threshold (approximately 1.23V), the switch turns on. By connecting a resistor divider from VIN to EN/UVLO to GND, the UVLO threshold on VIN can be set to any voltage between 2.7V and 18V. If UVLO is not needed, the EN/UVLO pin can be connected directly to VIN for always-on operation. The pin must not be left floating.

The device also has an internal UVLO on the VIN pin, with a typical threshold around 2.4V (rising) and 2.28V (falling), providing 125mV hysteresis (approximately 5% of the rising threshold). This ensures the device turns off when the input supply voltage drops too low, protecting downstream circuitry from brownout conditions.

The thermal shutdown feature protects the device from excessive junction temperature. When the junction temperature exceeds approximately 140C (typical), the internal MOSFET is turned off. The thermal shutdown has hysteresis, so the device does not restart until the junction temperature drops by approximately 20C. This protects the device in fault conditions such as output short circuit or excessive load current.

The TPS22810DBVR is the SOT-23-6 (DBV) tape-and-reel version. The TPS22810DRVR is the WSON-6 (DRV) version that supports 3A current. The -Q1 suffix indicates the AEC-Q100 automotive qualified version.

The TPS22810DBVR operates as an integrated N-channel MOSFET load switch with gate control, slew rate adjustment, and output discharge circuitry.

Integrated N-Channel MOSFET: The core switching element is an N-channel MOSFET connected between VIN and VOUT. Unlike P-channel load switches (which are common for high-side switching), the TPS22810 uses an N-channel MOSFET, which offers lower on-resistance per unit area than a P-channel MOSFET of the same die size. The N-channel MOSFET requires a gate voltage above the source (VIN) to turn on, which is provided by an internal charge pump or gate drive circuit. The RON of 79mOhm at VIN=12V is achieved through this N-channel architecture.

EN/UVLO Control: The EN/UVLO pin controls the on/off state of the internal MOSFET. When the EN/UVLO voltage exceeds the rising threshold (VENR, approximately 1.23V), the gate drive circuit turns on the MOSFET. When the EN/UVLO voltage falls below the falling threshold (VENF, approximately 1.13V), the MOSFET is turned off. The 100mV hysteresis between VENR and VENF prevents chattering when the EN/UVLO voltage is near the threshold. When the EN/UVLO voltage drops below the shutdown threshold (VSHUTF, approximately 0.4V), the device enters shutdown mode, drawing less than 1uA from the VIN supply.

Adjustable Rise Time (CT Pin): The CT pin controls the slew rate of the output voltage during turn-on. An internal current source charges an external capacitor connected from CT to GND. The voltage on the CT capacitor ramps linearly at a rate determined by the charge current and capacitance value. This ramp voltage is used as a reference for the gate drive circuit, controlling how quickly the MOSFET gate voltage increases, which in turn controls how quickly the output voltage rises. The rise time is approximately proportional to the CT capacitor value: larger CT capacitance = slower rise time. When CT is left floating, the device uses its internal capacitance for the fastest default rise time.

Quick Output Discharge (QOD Pin): When the switch is disabled (EN/UVLO = LOW), the QOD circuit connects a pull-down resistor (RPD, approximately 250 ohms typical) between VOUT and GND through the QOD pin. This actively discharges the output capacitor, causing the output voltage to decay exponentially. The discharge time constant is RPD x CL (plus any external resistor in the QOD path). When QOD is shorted directly to VOUT, the internal RPD value is used. When an external resistor is placed between VOUT and QOD, the total discharge resistance is RPD plus the external resistor. When QOD is left floating, the discharge function is disabled and the output floats. The QOD circuit is automatically enabled when the switch is disabled, regardless of the cause (EN/UVLO going low, UVLO tripping, or thermal shutdown).

Internal VIN UVLO: The device monitors the VIN voltage with an internal comparator. When VIN drops below the UVLO falling threshold (VUVF, approximately 2.28V), the MOSFET is turned off and the QOD is enabled. The UVLO has approximately 125mV hysteresis (VUVR minus VUVF), ensuring clean turn-on and turn-off behavior. This internal UVLO protects downstream circuitry from operating at voltages below the specified minimum.

Thermal Shutdown: A temperature sensor on the die monitors the junction temperature. When TJ exceeds the thermal shutdown threshold (approximately 140C typical), the MOSFET is turned off and the QOD is enabled. The device remains off until TJ drops below the thermal shutdown hysteresis point (approximately 120C), at which point the device restarts if the enable conditions are still met. The thermal shutdown is a last-resort protection mechanism and should not be relied upon for normal operation; proper thermal design must ensure TJ stays within the recommended operating range.