Board overview and PCB assembly
The Broadcom WICED Smart Tag based on BCM2073X chip is an evaluation board that is for
evaluation and troubleshooting.
Figure 1, 2 and Figure 3, 4 show the pictures of PCB boards’ real looking. In the next pages we
will explain the details for the HW working configurations based on power supply.
Figure 1: 20732 WICED Smart Tag Top View
Figure 2: 20732 WICED Smart Tag Bottom View
Figure 3: 20736//20737 WICED Smart Tag Top View
Figure 4: 20736 20737 WICED Smart Tag Bottom View
The WICED Smart Tag can be powered either by coil cell battery or 5V USB. Let’s have a look at the related schematic first:
20732 schematic drawing
20736// 20737 schematic drawing
Coin Cell battery powered
In the schematic drawing, two switchers are used--SW2 and SW3. When we choose VBAT directly for main power supply source:
- Pin 1 ,2
of SW2 need be connected, that’s to say physically disconnected U13 from the circuit to make Coin Cell battery directly power the system.
- At the same time pin 2 ,3 of SW3( for 20732 TAG board) or pin 1,2 of SW3( for 20736//20737 TAG board) need be connected together too.
On this case, VDDIO voltage value is exactly VBAT’s voltage value.
Further looking at different positions on the real PCB boards
Pull down SW3, pull up SW2 for 20732 TAG board
Pull up SW3, pull up SW2 for 20736//20737 TAG board
We also can have LDO U13 included to get an expected voltage value for VDDIO. If this is the case, pin 2 ,3 of SW2 and pin 1 ,2 of SW3(for 20732 TAG board) or pin 2,3 of SW3( for 20736//20737 TAG board) need be connected, by setting the different value of RFB1 and RFB2. We can get the different VDDIO value, the formula is:
VDDIO =3.3V; when RFB1= 470Kohm, RFB2=150Kohm
Physically PCB board switches indication
Pull up SW3, pull down SW2 for 20732 TAG board
Pull down SW3, pull down SW2 for 20736//20737 TAG board
If 5V_USB is selected for the main power supply source, pin 1,2 of SW2 and SW3 need be connected for 20732 TAG board; pin 2,3 of SW3, pin 1,2 of SW2 need be connected for 20736//20737 TAG board . In this way LDO U13 is necessary to be included into the power system for voltage converting, by setting the different value of RFB1 and RFB2. We can get the different VDDIO
value by the following formula:
For example, VDDIO =3.3V; when RFB1= 470Kohm, RFB2=150Kohm
20732 TAG board schematic indication and switches position
Pull up the switches like the picture showing
20736//20737 TAG board schematic indication and switches position
For switches, pull up SW2 and pull down SW3 in 20736//20737 TAG board