1. In home appliance application systems, the most commonly used AC to DC step-down circuit is RC method and then regulated with regulator, or step-down voltage with transformer and then use rectifier circuit to get the chip necessary DC 5V power supply. These two circuits, in AC power switch up and down time, because instant power on and power down, there may have a relatively short time of high amplitude pulse or burst on chips VDD power supply. By using Oscilloscope with high resolution, you can obviously observed pulse amplitude up to 70V or higher, as shown below:

2. In respond to the impact of such pulse, it is proposed to increase protection circuit in chip design aspects, and should pay attention to something in PCB Layout:

 (1)User must connect 104 capacitor on VDD in circuit design; connect a 5 ~ 10ohm resistor in series, which can effectively protect the chip from instant impact of high voltage pulse when power on. 

(2)In PCB Board Layout, please make sure that the VDD 104 capacitors and resistors as close to the chip as possible.