LE940B6 HW User Guide
Rev. 2.02
Page 95 of 111
2020-01-10
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 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.
Especially, a suitable bypass capacitor must be mounted on the following lines on the
application board:
•
VBATT & VBATT_PA (Pads
AP17,AP19,AR18,AR20,AS17,AS19,AT18,AU17,AU19,AT20)
Recommended values are:
•
100 uF for VBATT & VBATT_PA
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.
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