TDA5051 Datasheet, PDF (5/28 Pages) NXP Semiconductors – Home automation modem

Philips Semiconductors
Home automation modem
Product specification
TDA5051
FUNCTIONAL DESCRIPTION
Both transmission and reception stages are controlled
either by the master clock of the microcontroller, or by the
on-chip reference oscillator connected to a crystal.
This holds for the accuracy of the transmission carrier and
the exact trimming of the digital filter, thus making the
performance totally independent of application
disturbances such as component spread, temperature,
supply drift and so on.
The interface with the power network is made by means of
a LC network (see Fig.18). The device includes a power
output stage able to feed a 120 dBµV (RMS) signal on a
typical 30 Ω load.
To reduce power consumption, the IC is disabled by a
power-down input (pin PD): in this mode, the on-chip
oscillator remains active and the clock continues to be
supplied at pin CLK_OUT. For low-power operation in
reception mode, this pin can be dynamically controlled by
the microcontroller (see Section “Power-down mode”).
When the circuit is connected to an external clock
generator (see Fig.6), the clock signal must be applied at
pin OSC1 (pin 7); OSC2 (pin 8) must be left open. Use of
the on-chip clock circuitry is shown in Fig.7.
All logic inputs and outputs are compatible with
TTL/CMOS levels, providing an easy connection to a
standard microcontroller I/O port.
The digital part of the IC is fully scan-testable. Two digital
inputs, SCANTEST and TEST1, are used for production
test: these pins must be left open in functional mode
(correct levels are internally defined by pull-up/down
resistors).
Transmission mode
The carrier frequency is generated by the scanning of a
ROM memory under the control of the microcontroller
clock or the reference frequency provided by the on-chip
oscillator, thus providing strict stability with respect to
environmental conditions. High frequency clocking rejects
the aliasing components to such an extent that they are
filtered by the coupling LC network and do not cause any
significant disturbance. The data modulation is applied
through pin DATA_IN and smoothly applied by specific
digital circuitry to the carrier (shaping). Harmonic
components are limited in this process, thus avoiding
unacceptable disturbance of the transmission channel
(according to CISPR16 and EN50065-1
recommendations). A −55 dB total harmonic distortion is
reached when using the typical LC coupling network (or an
equivalent filter).
The D/A converter and the power stage are set in order to
provide a maximum signal level of 122 dBµV (RMS) at the
output.
The output of the power stage (TX_OUT) always has to be
connected to a decoupling capacitor, because of a DC
level of 0.5V_DD at this pin, present even when the device is
not transmitting. This pin also has to be protected against
overvoltage and negative transient signals. The DC
level of TX_OUT can be used to bias an unipolar transient
suppressor, as shown in the application diagram (see
Fig.18).
Direct connection to the mains is done through a LC
network for low-cost applications. However, a HF signal
transformer could be used when power-line insulation has
to be performed.
CAUTION
In transmission mode, the receiving part of the circuit is
not disabled and the detection of the transmitted signal
is normally performed. In this mode, the gain chosen
before the beginning of the transmission is stored, and
the AGC is internally set to −6 dB as long as DATA_IN
is LOW. Then, the old gain setting is automatically
restored.
Receiving mode
The input signal received by the modem is applied to a
wide range input amplifier with Automatic Gain Control
(AGC) (−6 to +30 dB). This is basically for noise
performance improvement and signal level adjustment
that ensures a maximum sensitivity of the A/D converter.
Then an 8 bit A/D conversion is performed, followed by
digital bandpass filtering, in order to meet the CISPR
normalization and to comply with some additional
limitations encountered in current applications. After digital
demodulation, the baseband data signal is made available
after pulse shaping.
The signal pin (RX_IN) is a high-impedance input, which has
to be protected and DC decoupled for the same reasons
as with pin TX_OUT. The high sensitivity (66 dBµV) of this
input requires an efficient 50 Hz rejection filter (realized by
the LC coupling network) also used as an anti-aliasing filter
for the internal digital processing (see Fig.18).
1997 Sep 19
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