LE910C1
Hardware User Guide
1VV0301298 Rev. 1.08 - 2017-11-14
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105 of 119
11.2.
Bypass Capacitor on Power Supplies
When a sudden voltage step is asserted to or a cut from the power supplies, the steep transition
causes some reactions such as overshoot and undershoot. This abrupt voltage transition can affect
the device causing it to not operate or to malfunction.
Bypass capacitors are needed to alleviate this behavior. The behavior can appear differently
depending on the various applications. Customers must pay special attention to this issue when
they design their application board.
The length and width of the power lines must be considered carefully and the capacitance of the
capacitors must be selected accordingly.
The capacitor will also prevent ripple of the power supplies and the switching noise caused in TDMA
systems such as GSM.
Especially, a suitable bypass capacitor must be mounted on the following lines on the application
board:
•
VBATT & VBATT_PA (M1, M2, N1, N2, P1, P2)
•
USB_VBUS (Pad A13)
Recommended values are:
•
100uF for both VBATT and VBATT_PA together
•
4.7uF for USB_VBUS (including the 1uF capacitor inside the module)
Customers must still consider that the capacitance mainly depends on the conditions of their
application board.
Generally, more capacitance is required when the power line is longer.
