Telit Wireless Solutions HE910-EU V2, Hardware User'S Manual

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When a sudden voltage is asserted to or cut from the power supplies,
The steep transition makes some reactions such as the overshoot and undershoot.
This abrupt voltage transition can affect the device not to work or make it malfunction.
The bypass capacitors are needed to alleviate this behavior and it can be affected
differently according to the various applications. The customers have to pay special
attention to this when they design their application board.
The length and width of the power lines need to be considered carefully and the
capacitance of the capacitors needs to be selected accordingly.
The capacitor will also avoid the ripple of the power supplies and the switching noise
caused in TDMA system like GSM.
Especially the suitable bypass capacitor must be mounted on the VBATT and VBATT_PA
lines in the application board.
The recommended values can be presented as;

100uF for VBATT and VBATT_PA
But the customers still have to consider that the capacitance mainly depends on the
conditions of their application board.
Generally more capacitance is required as the power line is longer.