DocID025421 Rev 1

5/19

AN4378

Application circuit

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Application circuit

Figure 2 shows the BlueNRG application board photo. The application is made up of 2

boards: a daughterboard and a motherboard. The daughterboard (Figure 1) holds the

BlueNRG with the circuits necessary for it to function. The Bluetooth Low Energy protocol

stack (GAP, GATT, SM, L2CAP, LL, RF-PHY) is embedded in the device.

For correct functioning, the daughterboard must be plugged into a motherboard (see

Figure 2) by two 5 x 2 header connectors (J6 and J7).

The motherboard includes an STM32L152VBT6 microcontroller to program the transceiver.

The microcontroller is programmed with firmware developed for the BlueNRG application. A

graphical user interface (GUI) is developed to correctly program the BlueNRG.

The daughterboard is equipped with a 16 MHz XTAL to provide the correct oscillator to the

BlueNRG. A low speed crystal oscillator is also mounted on the board and used by the

BlueNRG.

An internal SMPS is present on the BlueNRG to drastically reduce power consumption. The

SMPS is fed from the battery (2.0 V to 3.6 V) and provides a programmable voltage to the

device (1.4 V typically).

An SMA connector is included to connect the board to an antenna or to instrumentation to

verify correct functioning and to verify the FCC standard requests.

A few passive (inductors and capacitors) are used for matching/filtering of the power

amplifier (PA) and balun network for the receiver.

Figure 1. BlueNRG application daughterboard