NCN5192NGEVB
http://onsemi.com
6
C
2
, C
3
and C
14
are 100 nF ceramic decoupling capacitors
located directly adjacent to each power pin. For analog
power pins, an additional large-value ceramic capacitor may
be needed in addition to the 100 nF decoupling capacitor
when the application is intended for high-noise
environments.
For loop-powered devices, additional decoupling with a
large value capacitor is advised to prevent digital noise from
being transmitted on the current loop.
Additional ferrite beads in series with power supply lines
can help to reduce EMI.
Reference Voltages and Comparator Bias
NCN5192 needs an external analog reference voltage.
This reference is used by receiver or demodulator (RX)
comparator, carrier detect (CD), and voltage supervisor.
The AREF reference voltage sets the trip point of the
demodulation operational amplifier of the NCP5192. The
AREF reference voltage is also used in setting the DC
operating point of the received signal after it has passed
through the band-pass receive filter. The ideal value for the
AREF reference voltage depends on the voltage supply, and
is chosen roughly half-way the operating range of the
operational amplifiers. This ensures the range of the
operational amplifier is maximized. For operation at 3 V, a
1.24 V reference voltage is recommended. For operation at
5 V, a 2.5 V reference voltage is recommended.
For NCN5192NGEVB, a series regulator is used with an
internal reference of 1.25 V. The chosen regulator has a very
low supply current, to optimize power usage. Using a series
regulator is more desirable from a power usage perspective,
as a series regulator’s current draw will vary with the output
current, whereas a shunt regulator is dimensioned on the
maximum current draw and will always draw the same
current. Large capacitors on the in- and output of the voltage
regulator increase the reference stability.
The CDREF reference voltage sets the threshold for the
carrier detect comparator. As the received signal is biased at
AREF, the difference between CDREF and AREF will
determine the minimum amplitude needed for the carrier
detect comparator to flip. A (AREF-CDREF) of 80 mV
corresponds to signal of approximately 100 mV
peak-to-peak at the input of the receive filter. The CDREF
reference voltage on the NCN5192NGEVB is generated by
a resistor division of the AREF reference.
An external resistor is required to set the bias current. The
voltage over the bias resistor is regulated to AREF, so that
the resistor determines a bias current. This bias current
controls the operating parameters of the internal operational
amplifiers and comparators and should be set to
approximately 2.5
m
A. For low cost solutions, a 470 k
W
is
acceptable with minimal effect on operation.
Table 3. REFERENCE VOLTAGES
Description
Value
AREF Reference Voltage
1.248 V
CDREF Reference Voltage
1.163 V
Figure 6. Reference Voltages Schematic
www.BDTIC.com/ON/
