Output ripple noise is usually represented by peak- peak values. The main test methods are as follows:

1, Ground-line ring docking test

There are two noises of differential mode and common mode at the output end of DC-DC Converter, while the ripple noise is easily affected by the random noise and radiation noise in the environment. The parasitic inductance of the probe ground wire and the oscilloscope input capacitance form an LC resonant circuit, amplifying the high-frequency noise, and the probe ground wire senses the radiation noise of DC-DC Converters, so the probe ground wire must be removed. Therefore, in order to objectively measure the output ripple noise of the switch power supply, almost all power module manufacturers recommend the docking method (see FIG. 2), and the oscilloscope bandwidth is limited to 20MHz, and the 20MHz oscilloscope probe is used directly against the output foot to read out the ripple noise of DC voltage.

2, Parallel line test method

Be aimed at the standard brick DC-DC Converter, we recommend parallel line testing (see Figure 3).The length of two parallel copper foil bands are between 50.8mm (2in.) and 76.2mm (3in.) The spacing between the two parallel copper foil bands is 2.54mm(0.1in.)。The thickness and width of the copper foil belt are reasonably set to ensure that the total voltage drop of the current in the two copper foil belts is less than 2% of the module output voltage. On the copper foil band is 25.4mm from the module output (1in.) install a good high-frequency 1uF ceramic capacitor (X7R) or metal membrane capacitance (C1).Install a 10 uF (C 2) tantalum capacitance away from the oscilloscope 12.7mm(0.5in). Distance from the module output end of 50.8mm (2in.) To 76mm (3in.) Install the test point at the location. The spacing between V (+) test points and V (-) test points is 6.4mm (1 / 4in.). The oscilloscope was measured with a 20MHz broadband.