Service Guide

Wi-Fi&Bluetooth Module Series
FC908A_Hardware_Design 21 / 49
The FC908A is powered by VBAT. It is recommended to use a power chip with a maximum output current
of more than 0.5 A. To ensure better power supply performance, it is recommended to parallel 100 μF
decoupling capacitors and 1 μF and 100 nF filter capacitors near the input of the module VBAT.
Meanwhile, it is recommended to add a TVS tube near the VBAT input terminal to improve the surge
voltage bearing capacity of the module. In principle, the longer the VBAT line, the wider the line.
When paired with LTE, it is recommended to use 10 pF and 33 pF for C2/C4. The reference circuit of
VBAT input terminal is as shown in the figure below:
FC908A
VBAT
VBAT
D1
C2
C3 C4
NM
C1
100 μF
1 μF
100 nF
R1 0R
+
Figure 2: VBAT Circuit
The time sequence of FC908A power on and off is shown in the below:
VBAT
VDDIO
90% VH
2 Sleep Cycles
WLAN_EN
BT_EN
Sleep Clock
Figure 3: Power-up Timing
It is recommended that VBAT be powered on no later than VDDIO.
GND
1, 3, 20, 31, 33, 36
Ground