Safety Features of a Low Voltage Hot Swap Controller

Hot swap controllers allow a circuit board to be safely removed from or inserted into a live backplane. They limit inrush current and provide over-current protection.

The LTC4216 is designed to handle low supply voltages down to 0V. It also features an adjustable soft-start that controls the inrush current slew rate at start-up, important for large load capacitors used with low voltage boards.

Current Limiting

Inrush current limiting is a crucial feature of hot swap controllers. Rather than using a discrete circuit to control the inrush current, they sense when a board is being inserted or removed and regulate the power flow accordingly. This ensures that the device can be replaced without causing damage to the system.

Depending on the design, hot-swap voltage controllers can use two different schemes to limit current during insertion and removal of a line card. One technique involves using a PTC resistor to change its impedance and reduce current, while the other uses a MOSFET to monitor the drop across the drain-source junction. Both methods have advantages and disadvantages in terms of cost, response time and service life.

The first method limits current by charging a capacitor C1 across the gate-source junction of Q1. When the line card draws power, this charge dissipates through the sense resistor R2. As it discharges, R2 decreases its value, which increases Vgs and prevents Q1 from turning on. In this way, the controller can detect high inrush current and turn off the MOSFET if it is triggered.

In addition, the controller can measure the temperature of the MOSFET by measuring the voltage drop across its die. It can then determine if the MOSFET is overheating and take appropriate action. If the MOSFET overheats, it must be cooled to low voltage hot swap controller reduce power dissipation and prevent thermal shutdown of the controller and the rest of the circuit.

Short-Circuit Detection

In hot-swap applications, line card insertion causes a large and sudden “inrush” current that could destroy power supply filter capacitors or cause the backplane’s power supply to collapse. To protect against this, a hot-swap controller IC can detect the presence of short circuit conditions.

To do this, the hot swap controller monitors the voltage at an external N-channel power MOSFET’s gate. If the gate-drive voltage drops below a preprogrammed threshold, the controller turns off the MOSFET to limit current passing downstream. Some controllers also prevent the MOSFET from turning on by sensing its die temperature.

Unlike discrete-component schemes, which require larger primary power supplies and more robust wires and connectors, the IC-based solution is compact and cost effective. It also offers features such as a Status output (Power Good), thermal shutdown protection, undervoltage lockout, and an on/off control pin that shuts down the MOSFET.

When the system is powered up, the hot swap controller gradually decreases the voltage to its external FET and limits current through RSNS until the device is ready to be removed. It then either remains off (latch-off version) or attempts to restart (auto retry version) the device after its junction temperature has decreased. This allows a printed circuit board to be inserted and removed without damage. This minimizes downtime in mission-critical systems, which propels growth of the hot swap voltage controller market.

Undervoltage Lockout

The undervoltage lockout on a low voltage hot swap controller is an important safety feature that protects the system from damage or functional faults caused by line card removal. It works by gradually decreasing the voltage to the device until it is completely cut off, allowing it to be removed without damaging other circuits in the system.

To prevent the undervoltage lockout on a low-voltage hot swap controller from over-reacting to small changes in supply voltage, it is often used in conjunction with an RC network. This network helps the internal circuits of the device ride out output-short transients and adjacent board transients. This is achieved by connecting the RC network to the VCC pin of the hot-swap control.

Low voltage hot-swap controllers have many benefits that make them an attractive option for data centers and other electronic systems that require hot-swappable components. These devices help minimize downtime in mission-critical applications, and their ability to protect against power surges and other issues is driving their adoption. However, high costs and limited compatibility in device-functioning are major restraints to the growth of the microchip ic hot swap controller market. Fortunately, several new technologies are offering cost-effective alternatives, which are expanding the market for these devices. These devices also offer more features and are easier to integrate into the system. This is creating new opportunities for the low-voltage hot-swap controllers market.

Temperature Sensing

Hot-swap controller ICs prevent damage and operational faults in situations where a line card is inserted into a live backplane. The card’s power supply filter capacitors may discharge rapidly, demanding a sudden, high inrush current that can cause the backplane to collapse or overheat.

To control this inrush current, many hot-swap controllers use a power monitor that continuously samples the voltage on the UV pin and the OV pin. If these pins are below a threshold, the hot-swap output is pulled off (the FAULT and PWRGD pins are asserted). The power monitor also samples the temperature on an external NPN device. If the temperature rises above a threshold, the power monitor shuts down the MOSFET.

A common feature on modern low voltage hot-swap controllers is to reduce the power consumption of the auxiliary MOSFET by monitoring its die temperature and shutting it off when that temperature runs too high. This feature can be a big benefit for applications that require two separate power supplies to operate.

The power monitor on the ADM1278 also features a 12-bit ADC that can measure the voltage across the sense resistor, the supply voltage on the HS+ pin, and the output voltage. The data from the ADC can be read via a PMBus interface on the HS+ and HS- pins. This data can be used to optimize the performance of the ADRx MOSFETs and to detect overcurrent conditions.