For this test, the discrete bootstrap option, shown in Figure 4-19 was used. The default bootstrap supply was disconnected from the AMC0106M05 AVDD by removing R14. The discrete bootstrap supply consists of diode D1, the bootstrap resistor R34=3Ω, and the bootstrap capacitor C57=470pF. A very small value was intentionally chosen for C57 to generate a large bootstrap ripple voltage. The aim of the test was to evaluate how large AVDD supply voltage ripple affects the measurement accuracy of the AMC0106M05.

Figure 4-19 AMC0106M06 AVDD Bootstrap Configuration for This Test

Figure 4-20 shows the scope plot of the AVDD bootstrap supply voltage at a 10kHz PWM with 92.8% duty cycle. At this operating condition the off-time of the high-side GaN-FET, which equals the charging time of the bootstrap capacitor, was only 7.2µs.

The phase current measured with AMC0106M05 is identical to the measurement with the current probe. There is no performance degradation visible during the bootstrap charging time. The tolerance to high ripple voltage allows the use of smaller bootstrap capacitors, or, more importantly, operating at 100% duty cycle for longer periods of time.

Figure 4-20 Phase W Voltage at 10kHz PWM with 92.8% Duty Cycle, Phase Current W and AMC0106M05 AVDD

Figure 4-21 AMC0106M05 Measurement with OSR 32 at 3A vs Current Probe During Large AVDD Ripple