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Q: On the std 63030 EVM (HPA417) why is there output ripple, shown in the picture, under the following conditions:Vin = 4.5VVout = 3.3V.Iout = 100mA.Power save mode is OFF
When input voltage is less than 4.4V or greater than 4.6 V the ripple is gone.
A: The ripple will only occur at the point where the min inductor current is at 0mA and the device transitions to forced PWM mode. In this mode inductor current will be negative and current will be transferred from the output capacitor to the input capacitor. When min inductor current is greater than 0mA the device is in normal operation, nothing unique in this mode. But at the point where the device is transitioning we can see that it may move in and out of that mode. This is due to changes in efficiency and a rise in input voltage due to current transferred to the input capacitor.There is no risk of damage to the device.A Cff capacitor can be added, this will increase the AC gain which will help reduce the ripple.
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