UCC2915, UCC3915

15V PROGRAMMABLE HOT SWAP POWER MANAGER

SLUS198C – FEBUARY 2000 - REVISED - JUNE 2001

6

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

protecting the UCC3915 from voltage transients

The parasitic inductance associated with the power distribution can cause a voltage spike at VIN if the load

current is suddenly interrupted by the UCC3915. It is important to limit the peak of this spike to less than 15 V

to prevent damage to the UCC3915. This voltage spike can be minimized by:

D Reducing the power distribution inductance (e.g., twist the positive (+) and negative (–) leads of the power

supply feeding VIN, locate the power supply close to the UCC3915 or use PCB power and ground planes).

D Decoupling VIN with a capacitor, CIN (refer to Figure 1), located close to the VIN pins. This capacitor is

typically 1

µF or less to limit the inrush current.

D Clamping the voltage at VIN below 15 V with a Zener diode, D1(refer to Figure 1), located close to the VIN

pins.

Figure 2. Load Current, Timing-Capacitor Voltage, and Output Voltage of the UCC3915

Under Fault Conditions

estimating maximum load capacitance

For hot-swap applications, the rate at which the total output capacitance can be charged depends on the

maximum-output current available and the nature of the load. For a constant-current, current-limited

application, the output will come up if the load asks for less than the maximum available short-circuit current.

To ensure recovery of a duty cycle from a short-circuited load condition, there is a maximum total output

capacitance which can be charged for a given unit on time (fault time). The design value of on or fault time can

be adjusted by changing the timing capacitor CT.