A hot-swap power manager (HSPM) can be used to design a simple, programmable, constant-current electronic load for 3-V to 5-Vdc power rails. Ordinarily, maximum current capability is limited to 2.7 A for this part type, but higher currents can be obtained using external n-channel MOSFETs. The current would then be limited only by the safe operating area of the FET. An undervoltage lock-out trigger on the Unitrode UCC3919 prevents operation when the input power rail is below 2.75 V.
The circuit can also be configured to operate as a pulsed load. In pulse mode, load current will be demanded in pulses with user-programmable pulse width, leading edge rate and maximum current level (IMAX). Operation of the HSPM as an electronic load is based on the on-chip linear-current amplifier that controls the MOSFET gate voltage to equalize the voltage drops across R1 and RS relative to VDD. The load current is programmed by R1, R2 and RS as defined by: IMAX = R1 |VIBIAS|/(R1 + R2) RS amps,where VIBIAS is the voltage (1.5 V) on the IBIAS pin relative to VDD.