AN752 pdf datasheet

APPLICATION NOTE 752
Creating a Fast Load Transient
Abstract: A simple circuit generates fast load transients for thorough testing of power supplies.
Many of Maxim's devices show a typical operating characteristic (TOC) graph with a very fast load transient. Our
customers sometimes ask us how we create such fast changes in load. Although commercially available dynamic
load boxes are capable of supplying transients, they do not provide the fast rise times and fall times necessary
for an attractive-looking TOC.
To obtain fast load transients, we combine a power MOSFET and a couple of resistors right on the PC board of
the device under test (DUT). Choosing the components is relatively easy. If the output voltage is positive, an nchannel
MOSFET works great. The MOSFET is connected with a resistor from the source to ground (see Figure
1). The MOSFET's gate is terminated with a 51W resistor to impedance-match the signal generator's output.