10 Application Guide
10.1 Debug the FN990 Family Module in Production
To test and debug the FN990 Family module integration, it is strongly recommended to
add test pins on the host PCB for the following purposes:
• Checking the connection between the FN990 Family itself and the application
• Testing the performance of the module by connecting it to an external computer
Depending on the customer application these test pins include, but are not limited to, the
following signals:
• FULL_CARD_POWER_N, SYS_RESET_N, W_DISABLE_N, PCIE_WAKE_N
• VPH_PWR, GND
• VREG_L6B_1P8
• USB_D +/-
• USB_SS_TX/RX_M/P
• PCIE_TX/RX_M/P
10.2 Bypass Capacitor on Power Supplies
When a sudden voltage step is asserted to or a cut from the power supplies, the step
transition causes effects such as overshoot and undershoot. This abrupt voltage transition
can affect the device causing it to fail or to malfunction.
Bypass capacitors are needed to alleviate this behavior, which can appear differently
depending on the various applications. Integrators must pay special attention to this issue
when they design their application board.
The power lines length and width must be considered carefully, and the capacitors value
must be selected accordingly.
The capacitor will also prevent power supply ripple and the switching noise caused in
TDMA systems, such as GSM.
Most important, a suitable bypass capacitor must be mounted on the following lines on
the application board:
•
VPH_PWR
Recommended value:
•
100 uF for VPH_PWR
It must be considered that the capacitance mainly depends on the application board.
Generally, additional capacitance is required when the power line is longer.
Furthermore, if the fast power-down function is used, an additional bypass capacitor
should be mounted on the application board.
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