User's Guide
LE910Cx HW User Guide
Doc#: 1VV0301298
Rev. 13.0 Page 101 of 124 2019-06-07
Bypass Capacitor on Power Supplies
When a sudden voltage step to or a cut from the power supplies is asserted, 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 behaviour. The behaviour 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.