These days I assembled a second prototype of BBRF103 receiver. Here are some notes.
I made a different power harness. The purpose is to allow the circuit to be powered by the USB cable with VBUS or via a separate 5Volt power connector.
So far in the diagrams of BBRF103 the input of the 5V power supply to the PCB is taken from the VBUS of CYUSB3KIT-003.
I noticed on my two prototypes some problem related to the intervention of the protection circuit (U11 sheet 2 of 8, CYUSB3KIT scheme) on the Cypress plate and caused by the current increase required in some phases of power-up of the PCB BBRF103 and R820T2 use.
I modified the input of the 5Volt and connected it upstream of the protection circuit using the J3 jumper as a connector.
The scheme is as follows:
The current consumption of complete BBRF103 using Tuner R820T2 is about 530mA at 5Vdc.
From left to right
- 5Volt dc external input (optional)
- latched pushbutton VBUS / extenal 5V
- USB3 connector
- ON / OFF
The box used is made of aluminum, it has dimensions 100x76x35mm, currently at Banggood it is available only in a golden color. The surface is brushed and treated with an insulating process so it is necessary to sandpaper the contact surfaces to obtain an electrical contact when it closes.
In the grooves on the long sides I inserted after scratching the rail a strip of Desoldering Copper Wick as a contact gasket.
The ADC LTC2217 and the tuner R820T dissipate more than one Watt in heat. To keep the temperature of the chips lower, I tried two passive aluminium heat sinks that lead the heat to the aluminium box, which acts as a heat sink, reducing the temperature of the chips by 20-30° C.
The radiators are fixed with some M2 nylon insulating screws and nuts. I used a slightly modified PCB from BBRF103-2 layout.
Stand alone static current test
Assembling the pcb I have tried a simple method to verify errors of power supply rails.
Each block of the circuit is powered separately through a filter inductor. So not mounting these components it is easy to measure the current absorbed by various blocks on the PCB BBRF103-2 before connecting the CYUSB3KIT-003 board.
Here is a table with the measured power consumption of three blocks in a static way.
I have not mounted FL1, FL2, FL3.
I connected a 5Volt /500mA power supply to the LDO power supply of the plate and
I measured the current at the unassembled inductors by injecting an external voltage, getting:
|Oscillator SI5351||15-16 mA||FL3 / external power supply 3.3V|
|Tuner R820T2||80-85 mA||FL2 / external power supply 3.3V|
|ADC LTC2217||269-210 mA||FL1 / external power supply 5V (ADC gets 3.3V via LDO)|
In case, inspect the component mounting and check the welds with a microscope or lens.