LM5069MM-2/NOPB

The LM5069MM-2/NOPB is a positive high-voltage hot swap and inrush current controller with power limiting, manufactured by Texas Instruments. It provides intelligent control of power supply connections during insertion and removal of circuit cards from a live system backplane or other hot power sources, operating over a wide input voltage range of 9V to 80V.

The LM5069 controls an external N-channel MOSFET as a series pass element, providing inrush current limiting to minimize system voltage droop and transients during hot insertion. Both the current limit and maximum power dissipation in the external MOSFET are programmable, ensuring the MOSFET operates within its Safe Operating Area (SOA) under all conditions. This power-limiting feature is critical for protecting the MOSFET during startup into capacitive loads or during fault conditions.

The device features programmable undervoltage lockout (UVLO) and overvoltage lockout (OVLO) with adjustable hysteresis, allowing the system designer to define the valid input voltage operating window. A programmable insertion delay timer allows system ringing and transients to settle after physical insertion before the power path is enabled, preventing false fault triggers. A programmable fault timer filters out transient fault conditions while still protecting against sustained overloads.

The POWER GOOD output (active-high, open-drain) indicates when the output voltage is within 1.25V of the input voltage, providing a status signal to the system. The -2 suffix designates the auto-retry version: after a fault condition is detected and the fault timer expires, the LM5069-2 automatically retries with a fixed duty cycle, re-attempting to power the load without requiring manual intervention or power cycling. This contrasts with the -1 version, which latches off after a fault and requires a power cycle or UVLO toggle to restart.

The LM5069 includes an internal charge pump and gate driver for the external N-channel MOSFET, eliminating the need for external gate drive circuitry. The device operates from -40°C to +125°C and is housed in a 10-pin VSSOP (DGS) package measuring 3 x 3 mm. It is available in tape and reel packaging with MSL-1 rating.

The LM5069MM-2/NOPB operates as a hot swap controller that manages the power-up sequence and fault protection of an external N-channel MOSFET connected in series between the input supply and the load.

Power-Up Sequence: When a circuit card is inserted into a live backplane, the input voltage appears at the VIN pin. The UVLO and OVLO comparators check whether the input voltage is within the programmed valid operating window. If within range, the insertion timer starts. This timer allows contact bounce and input ringing to settle before enabling the power path. After the insertion timer expires, the gate driver begins charging the gate of the external MOSFET via the GATE pin, turning it on gradually.

Inrush Current Limiting: The LM5069 monitors the voltage across a current-sense resistor connected between VIN and the SENSE pin. During startup, the controller regulates the MOSFET gate voltage to limit the inrush current to the programmed value set by an external resistor on the ISET pin. This controlled current limit charges the output capacitors at a controlled rate, preventing the large transient current that would otherwise flow if the MOSFET were turned on instantly. The result is a controlled, linear ramp-up of the output voltage, minimizing input supply droop and eliminating the risk of connector damage from inrush surges.

Power Limiting: The LM5069 implements a unique power-limiting function that monitors both the current through and the voltage across the external MOSFET simultaneously. The power dissipation in the MOSFET is calculated as P = VDS × ID. The programmable power limit (set by the PLIM pin resistor) ensures that even during the extended period when the MOSFET is partially on (large VDS combined with moderate ID), the MOSFET never exceeds its SOA. If the calculated power exceeds the programmed limit, the gate voltage is reduced to limit current further. This feature is essential for safely starting into large capacitive loads where the MOSFET must dissipate significant energy during the charging period.

Circuit Breaker: For severe overcurrent events (such as a short circuit at the output), the LM5069 provides a fast-acting circuit breaker function. When the sense voltage exceeds approximately twice the programmed current limit threshold, the gate is immediately pulled low to turn off the MOSFET, and the fault timer is initiated.

Fault Timer and Auto-Retry (-2 Version): When a fault condition is detected (overcurrent, over-temperature, or UVLO/OVLO trip), the fault timer starts counting. If the fault persists beyond the programmed fault time, the MOSFET is turned off. In the LM5069-2 auto-retry version, the device waits for a retry period (approximately 16x the fault time) and then automatically attempts to restart. This cycle repeats with a fixed duty cycle (approximately 6% on-time) until the fault clears, at which point normal operation resumes. This auto-retry behavior is ideal for unattended systems where manual intervention is impractical.

UVLO and OVLO: The undervoltage and overvoltage lockout comparators monitor the input voltage through external resistor dividers on the UVLO and OVLO pins. The hysteresis for each is independently programmable via external resistors, allowing precise control of the enable and disable thresholds. When UVLO or OVLO trips, the MOSFET is turned off and the fault handling sequence begins.

POWER GOOD Output: The PWRGD pin is an open-drain output that goes HIGH-impedance (requires external pull-up) when the output voltage is within 1.25V of the input voltage, indicating the power path is fully established. This signal can be used to enable downstream circuitry or as a system status indicator.