Optical isolation probe actual test case-GaN half-bridge upper tube test

Test background

Location: A well-known foreign brand semiconductor company, Shenzhen Gallium Nitride Laboratory

Test object: Gallium nitride half-bridge fast charging

Test reason: Because the high-voltage differential probe will explode when testing the Vgs of the half-bridge upper tube, it is necessary to conduct a thorough test on the specific parameters of the half-bridge upper tube control signal.

Test probe: Maxin OIP series optical isolation probe

site conditions

Because the design density of this gallium nitride fast-charging PCBA is very high, and the resistor and capacitor use 0402 devices, the coaxial extension cable can only be used for connection, which is not the optimal solution (MCX female socket connection is usually recommended to minimize lead errors).

The on-site connection diagram is as follows:

▲Figure 1: Wiring

Field testing steps

1. Connect the probe to the 10X attenuator and insert the attenuator into the coaxial extension cable;

2. Connect the OIP probe to channel 4 of the oscilloscope and turn it on;

3. Set the attenuation ratio of the corresponding channel of the oscilloscope to 10X, and set the input resistance to 50Ω;

4. Power on the target board;

▲Figure 2: Test scenario 1

▲Figure 3: Test scenario 2

Test Results

1.Vgs control voltage is about 5.1V, the signal is smooth without any distortion;

2. The negative surge at the moment when the upper tube is turned off is about 0.5V, which is within the safe range of gallium nitride devices;

3. The negative surge caused by the moment when the lower tube is turned off is around 2.2V, which is within the safe range of gallium nitride devices;

4.Vgs signal rise time is about 240ns.

(The above data is read through screenshots)

▲Figure 4: Screenshot of test results

in conclusion

1. The target board is reasonably designed and the Vgs control signal is almost perfect;

2. The test shows that the Vgs signal does not have any oscillation, and the common mode interference is completely suppressed;

3. The OIP series optical isolation probe tested the Vgs of the gallium nitride half-bridge upper tube and did not cause the tube to explode.