0 Replies Latest reply on Dec 1, 2014 10:37 PM by liumin

    BCM92073X TAG Power Supply Configurations

    liumin

      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.

       

      1.png

      Figure 1: 20732 WICED Smart Tag Top View

       

      2.png

       

       

      Figure 2: 20732 WICED Smart Tag Bottom View

       

      3.png

       

      Figure 3: 20736//20737 WICED Smart Tag Top View

      4.png

      Figure 4: 20736 20737 WICED Smart Tag Bottom View

       

       

      Power configurations

      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

      5.png

       

      20736// 20737 schematic drawing

      6.png

      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.

      7.png

      8.png

       

       

      Further looking at different positions on the real PCB boards

      Pull down SW3, pull up SW2 for 20732 TAG board

      9.png

      Pull up SW3, pull up SW2 for 20736//20737 TAG board


      10.png

       

      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=0.8X (RFB1+RFB2)/RFB2

      For example,
      VDDIO =3.3V; when RFB1= 470Kohm, RFB2=150Kohm

      11.png
      12.png

       

      Physically PCB board switches indication

      Pull up SW3, pull down SW2 for 20732 TAG board

      13.png

       

       

      Pull down SW3, pull down SW2 for 20736//20737 TAG board

      14.png

       

      5V_USB powered

       

      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:       
      VDDIO=0.8X(RFB1+RFB2)/RFB2

      For example, VDDIO =3.3V; when RFB1= 470Kohm, RFB2=150Kohm

      20732 TAG board schematic indication and switches position

      16.png

      Pull up the switches like the picture showing


      17.png

      20736//20737 TAG board schematic indication and switches position

      18.png

       

      For switches, pull up SW2 and pull down SW3 in 20736//20737 TAG board

      19.png