AN4647 datasheet(4/9 Pages) STMICROELECTRONICS

4 / 9 page

USB grid charger

AN4647

4/9

DocID027372 Rev 1

USB grid charger

To measure inrush current in fuse, a commercial grid USB charger is used.

Following severe conditions are applied:

•

100 000 inrush surges (50 plug-in by day during 5 years)

•

Ambient temperature = -30, 25°C and 85°C

Figure 2 shows the experimental setup used to measure inrush current with a grid charger.

Figure 2. Grid charger experimental setup

The grid charger is connected between Vbus and GND of the characterization board.

To charge Cload, the current flows through the CBTVS2Axx-1F3 and oscilloscope current

probe measures it. A voltage probe measures voltage at Cload edge.

With MOS2 open, switching on MOS1 connects charger to CBTVS2Axx-1F3 and Cload.

Figure 3 shows a measurement of inrush current with Cload = 22 µF and 85 °C.

Figure 3. Inrush current measurement example with grid charger (Cload = 22 µF / 85°C)

It presents 5.6 A maximum and 12.5 µs width. A small oscillation is present due to the LC

circuit formed by cable inductances and Cload capacitor. When load voltage is stabilized at 5

V, inrush current is at 0 A.

AN4647 Datasheet(PDF) 4 Page - STMicroelectronics