ZHCSHW4A December 2017 – January 2019 TPS23523
PRODUCTION DATA.
The table below summarizes the design parameters that must be known before designing a hot swap circuit. When charging the output capacitor through the hot swap MOSFET, the FET’s total energy dissipation equals the total energy stored in the output capacitor (1/2CV2). Thus both the input voltage and output capacitance will determine the stress experienced by the MOSFET. The maximum load power will drive the current limit and sense resistor selection. In addition, the maximum load current, maximum ambient temperature, and the thermal properties of the PCB (RθCA) will drive the selection of the MOSFET's RDSON and the number of MOSFETs used. RθCA is a strong function of the layout and the amount of copper that is connected to the drain of the MOSFET. Air cooling will also reduce RθCA substantially. Finally, it's important to know what transients the circuit has to pass in order to size up the input protection accordingly.
| DESIGN PARAMETER | EXAMPLE VALUE |
|---|---|
| Input voltage range | –38 V to –60 V |
| Maximum Load Power | 400 W |
| Output Capacitance | 660 µF |
| Location of Output Cap | After EMI filter with ~5 µH of inductance. |
| Maximum Ambient Temperature | 85°C |
| MOSFET RθCA (function of layout) | 20°C/W |
| Pass “Hot-Short” on Output? | Yes |
| Pass a “Start into short”? | Yes |
| Is the load off until PG asserted? | Yes |
| Max Input Inductance | 10 µH |
| Level of IEC61000-4-5 to pass | 2-kV Line to Line with 2-Ω series impedance |
| Pass Reverse Hook Up | Yes |