1. Core Function: Controlled Power-Up and Inrush Current Limitation

️· The HV302/HV312 is designed to enable the safe insertion of circuit cards into powered systems (hot swapping) without causing damaging inrush currents or disturbances on the backplane power rails.
️· It achieves this by controlling the power-up sequence of the inserted card, ensuring a gradual and controlled ramp-up of current.

2. Operational Modes

The device operates in two main modes:

️· Servo Mode: This mode dynamically controls the current using a feedback loop involving the sense resistor and the RAMP pin. It precisely limits the inrush current and manages the ramp-up of the load capacitor voltage.
️· Feedback Capacitor Mode: This mode uses the discharge and charge of a feedback capacitor alongside the ramp capacitor to control the inrush current and timing of the power-up.

3. Start-Up Sequence and Key Stages

1. Initial Power-Up & Internal Regulation: On initial power application, an internal circuit holds off the external MOSFET until an internal regulator reaches approximately 10V. This prevents glitches during the internal start-up.
2. Voltage & Current Monitoring: The device checks input UV (under-voltage) and OV (over-voltage) limits.
3. Ramp-Up Phase (Controlled Current): The current source connected to the RAMP pin is activated. The RAMP capacitor and feedback capacitor are either charged or discharged based on mode.
4. MOSFET Turn-On: Once the RAMP voltage exceeds the threshold, the controller begins turning on the external MOSFET.
5. Current Limiting & Load Capacitor Charging: The feedback loop (Servo Mode) or capacitor discharge (Feedback Capacitor Mode) controls the rate of current increase, limiting the inrush current and charging the load capacitor on the inserted card.
6. Activation & Sleep Mode: Once the load capacitor is charged and the current is stable, the controller fully activates the MOSFET, enabling the card and entering a low-power sleep mode.
7. Monitoring and Reset: The device continuously monitors the current and voltage, resetting the system if limits are exceeded.

4. Protection Features

️· Over-Current Protection: A circuit breaker trips within 5µs if the current exceeds a threshold, protecting the system from damage.
️· Over/Under Voltage Protection: The device resets if the input voltage falls outside programmed limits.
️· Auto-Retry Mechanism: If a fault occurs, an auto-retry timer allows the device to cool down and attempt restart. This can be disabled.

5. Key Signals & Components

️· RAMP Pin: Drives the ramp capacitor, sets timing and controls current during startup.
️· SENSE Pin: Monitors current flowing into the load, used for current limiting.
️· External MOSFET: Controlled by the device to switch power to the inserted card.
️· Load Capacitor: The capacitance of the inserted card, which needs to be charged.
️· PWRGD Flags (A, B, C, D): Indicate the completion of each stage of the power-up sequence.

6. Design Considerations

️· The values of external components (resistors, capacitors) determine the timing, current limits, and protection thresholds.
️· The device can be configured for different applications and load characteristics.



In essence, the HV302/HV312 is a sophisticated power management IC designed to facilitate safe and reliable hot swapping of circuit cards, protecting both the system and the inserted card from damage caused by inrush currents and other potential issues.