The power ripple index of the DC/DC module is an important parameter. A clean power supply is a prerequisite for the stable operation of the digital circuit and an important guarantee for the parameters of the simulator. To determine the power quality, the Output Ripple of the DC/DC module must be measured. However, the ripple value measured by many people is usually hundreds of music videos or even hundreds of music videos, which is far greater than the maximum ripple value provided by the device manual, this is mainly caused by incorrect measurement methods.
Correct Measurement Method
1) limits the oscilloscope bandwidth to 20 MHz (most of the low-end and Middle-end oscilloscope stalls are limited to 20 MHz, and high-end products also have a MHz bandwidth limit ), the purpose is to avoid the impact of high-frequency noise on the ripple measurement of digital circuits, so as to ensure measurement accuracy as much as possible.
2) set the coupling mode to AC coupling to facilitate measurement (observe the ripple with smaller gear positions and do not care about the DC level ).
3) ensure that the probe grounding is as short as possible (the main reason for measuring the ripple is that the grounding line is too long). Try to use the original test short needle that comes with the probe. If no short needle is tested, the grounding wire and shell of the probe can be removed to expose the probe's crust. The self-made grounding wire is wound on the probe's crust to ensure that the length of the grounding wire is less than 1 cm.
4) The oscilloscope is suspended, and only the probe is used to share the ground with the reference point of the test signal. Do not use other methods to share the ground with the test device. This will introduce a great deal of ground noise to the ripple measurement. For example, when the oscilloscope and other instruments co-plug the board, the switches of other instruments may pass through the ground to bring noise interference to the test.
Among them, 3rd are critical. If the grounding line is too long, the inductance effect will introduce additional noise to the measurement system, as shown in.
Oscilloscope parameter requirements: supports bandwidth limit function: Generally, an oscilloscope supports 20 MHz bandwidth limit, for example, SDS 1102CM.
Probe requirements: in order to make the ground as short as possible, try to use the original test of the probe short needle, if there is no original test short needle, you must make a short ground: remove the probe ground cover, use a wire to self-bypass the grounding short line. We recommend copper wire in five category lines with moderate strength (or some of them are soft, please recommend better ). Other candidates include solder wires and knives. When 1x is selected, the bandwidth of the passive probe is generally limited to 6 MHz/10 MHz when it is located at 1x. This effectively filters out high-frequency noise interference at the front end, reduce the influence of ripple measurement.