User's Manual

LE940B6 Hardware User Guide
1VV0301331 Rev. 1.8 - 2017-03-15
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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.
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.