Wi-Fi&Bluetooth Module Series
FC909A_Hardware_Design 21 / 49
The following figure shows the recommended power on/off sequences for the module:
VBAT
VDDIO
90% VH
2 Sleep Cycles
WLAN_EN
BT_EN
Sleep Clock
Figure 2: Power On Timing
It is recommended that VBAT shall be powered on no later than VDDIO.
3.3.2. Buck Circuit Pins
Table 6: Definition of Buck Circuit Pins
VIN_LDO_OUT/VIN_LDO is the output and input pins of the buck circuit inside the module, and pin 20 is
the dedicated GND pin of the buck circuit. Because the buck circuit is prone to high-frequency noise, so
please pay attention to it. It is recommended to use 2.2
μH inductors such as TFM201610ALM-2R2MTAA
(TDK) and 4.7
μF capacitors to ensure that the traces are as short as possible and the trace width shall
not be less than 0.4 mm. At the same time, it is recommended to route the traces away from sensitive
signals.
The following is the buck circuit reference circuit and recommended inductance parameter:
Pin Name
Pin No.
Description
Min.
Typ.
Max.
VIN_LDO_OUT
21
Internal buck output for the module
-
-
-
VIN_LDO
23
Internal buck input for the module
-
1.35
-
GND
20
Buck circuit dedicated GND pin