NCN51205GEVB
http://onsemi.com
15
FUNCTIONAL DESCRIPTION
Because the NCN5120 Development Board contains the
NCN5120 KNX Transceiver (KNX Certified) no details on
KNX will be given in this document. Detailed information
on the Certified KNX Transceiver NCN5120 can be found
in the NCN5120 datasheet (www.onsemi.com). Detailed
information on the KNX Bus can be found on the KNX
website and in the KNX standards (www.knx.org).
KNX Bus Connection
Connection to the KNX bus is done by means of J1. A
standard Wago connector (type 243
−
211) can be used for
this (see Figure 18). A reverse protection diode (D1,
Figure 11) is foreseen (mandatory) as also a Transient
Voltage Suppressor (D2, Figure 11).
Figure 18. KNX Bus Connector
Adjustable DC
−
DC Converter
NCN5120 provides the power for the complete reference
design. It has also a second power supply which can be used
to drive external loads. The voltage is programmable
between 3.3V and 21V by means of an external resistor
divider (R6 and R9, see Figure 11). The voltage divider can
be calculated as next:
R
6
+
R
9
R
VDD
2
M
R
9
)
R
VDD2M
V
DD2
*
3.3
3.3
(eq. 1)
R
VDD2M
is between 60 k
W
and 140 k
W
(typical 100 k
W
).
The DC value of the KNX bus should be higher than V
DD2
.
Be aware that when changing the V
DD2
voltage, D9
…
D12
(see Figure 11) need to be replaced. Check the SMFxxA
product family for possible replacements
(www.onsemi.com).
Although V
DD2
is capable of delivering 100 mA, the
maximum current capability will not always be usable. One
needs to make sure that the KNX bus power consumption
stays within the KNX specification. The maximum allowed
current for V
DD2
can be calculated as next:
V
BUS
I
BUS
w
2
ƪ
0.033
)
ǒ
V
DD2
I
DD2
Ǔ
ƫ
(eq. 2)
I
BUS
is limited by NCN5120. If J5 is open, I
BUS
can
maximum be 12.5 mA. If J5 is shorted, I
BUS
can maximum
be 25 mA. I
BUS
will however also be limited by the KNX
standard. Minimum V
BUS
is 20 V (see KNX standard).
Above formula gives only an estimation and will mainly
depend on the firmware loaded on the microcontroller (U2,
see Figure 11). One must always verify that the KNX bus
loading is in line with the KNX Specification under all
operating conditions!
Xtal Oscillator
A crystal of 16 MHz (Y1, see Figure 11) is foreseen on the
development board. This clock signal is also supplied to the
microcontroller. See the NCN5120 datasheet
(www.onsemi.com) for more details on this signal.
RESETB and SAVEB
The KNX transceiver NCN5120 controls the reset state of
the microcontroller by means of the RESETB signal. An
additional signal SAVEB can be monitored by the
microcontroller to detect possible issues. See NCN5120
datasheet for more details on these two signals.
Voltage Supervisors
NCN5120 has different voltage supervisors. Please check
the NCN5120 datasheet for more details.
Temperature Monitor
NCN5120 produces an over-temperature warning (TW)
and a thermal shutdown warning (TSD). Please check the
NCN5120 datasheet for more details.
External IO
The development board has the possibility to monitor up
to 8 inputs (pin 1, 3, 5, 7, 9, 11, 13 and 15 of J3) and control
up to 4 outputs (pin 1, 3, 5 and 7 of J3). Notice that 4 of the
inputs are shared with 4 of the outputs (pin 1, 3, 5 and 7 of
J3). By default the board has 4 inputs (pin 9, 11, 13 and 15
of J3) and 4 outputs (pin 1, 3, 5 and 7 of J3). To use the
additional 4 inputs, Q1
…
Q4 need to be removed and R12,
R17, R22 and R25 need to be mounted. The input pins are
3.3 V compliant and ESD protected (D5
…
D8, Figure 11).
J3 is connected in such a way that an easy connection
between the input and ground is possible (pin 9, 11, 13 and
15 of J3). The microcontroller (U2, see Figure 11) should be
configured with an internal pull-up (see microcontroller
datasheet on how to do this).
The external outputs are driven by means of low-side
drivers (Q1
…
Q4, see Figure 11). A gate resistor is foreseen
for slope control (R15, R18, R23 and R26 of Figure 11). J3
is routed in such a way that the load can easily be connected
between the output (low-side driver) and V
DD2
. Q1
…
Q4
can be used over the complete V
DD2
voltage range. ESD
diodes D9
…
D12 need to be replaced if V
DD2
is increased
(see also Adjustable DC-DC Converter).
Push Button and LED’s
One push button (SW1) and 3 LED’s (LED1
…
LED3)
are foreseen on the reference design. These are freely usable.
