MicroBCU2

MicroBCU2
Developer	SirSydom
Status	beta
Version	V00.20
Microcontroller/Board	universal

Description

A a compact bus coupling unit for KNX building automation based on the NCN5120 knx transceiver. It serves as a power supply and UART access to KNX bus.

Hardware

• IC: NCN5120 (ready for NCN5121 / 5130)
• Size: 23 x 19 x 9 mm
• Weight: about 4g
• Voltage 1: 3.3V
• Voltage 2 (optional): 5V (default), can be changed: 3.3V - 21V
• Ripple at VCC1+2: about 50mV
• Max. current: up to 100mA
• UART: 19200bps 8E1 / 3.3V

User Documentation

Soldering the Kit

MicroBCU2 comes as a kit where the big parts on the bottom side have to be soldered:

• C4 - 100µF / 35V electrolytic capacitor. Polarization is important, refer to silkscreen or photo
• C41 - 1µF MLCC 1206
• L1 and L2 - 220µH inductors
• R1 - 22R resistor 2512
• J1 - 7x1 2.54 pin header (or whatever you need to connect to your host PCB)
• D1 - SS16 reverse polarity protection diode. . Polarization is important, refer to silkscreen. The bar on the diode should match the bar on silkscreen.
• D2 - SMAJ40CA TVS diode

I recommend to solder the parts in this order: L1, L2, C4, C41, R1, D1, D2, J1

Deactivate / Change VCC2

If you want to get rid of VCC2, L2, R3, R4, R5, C11 and C111 are not needed. Close J2 in that case.

To change VCC2, change R4 and R5 according the NCN5120 dataheet. When VCC2 is greater than 10V, C11 must be changed so that the voltage rating matches or exceeds VCC2 (e.g. when VCC2 = 12V, use a 16V MLCC)

Enable High Bus current

For bus current consumption up to 20mA, J3 must be closed (This is the default, closed by a 0R resistor).

For bus current consumption of 10mA or less, J3 can be open.

Schematic

Schematic V00.20

Developer Documentation

Version history

• V00.11 - first prototype series
• V00.20 - second prototype series

Links

Vorstellungs- / Entwicklunsthread im KNX User Forum

1. Sammelbestellung im KNX User Forum

OnSemi NCN5120 Datasheet

MicroBCU2 on GitLab