MC145502 데이터 시트보기 (PDF) - Motorola => Freescale
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MC145502 Datasheet PDF : 28 Pages
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RxO, RxO
Receive Analog Outputs
These two complimentary outputs are generated from the
output of the receive filter. They are equal in magnitude and
out of phase. The maximum signal output of each is equal to
the maximum peak–to–peak signal described with the refer-
ence. If a 3.15 V reference is used with RSI tied to VAG and a
+ 3 dBm0 sine wave is decoded, the RxO output will be a
6.3 V peak–to–peak signal. RxO will also have an inverted
signal output of 6.3 V peak–to–peak. External loads may be
connected from RxO to RxO for a 6 dB push–pull signal gain
or from either RxO or RxO to VAG. With a 3.15 V reference
each output will drive 600 Ω to + 9 dBm. With RSI tied to VDD,
each output will drive 900 Ω to + 9 dBm.
RxG
Receive Output Gain Adjust (MC145502 Only)
The purpose of the RxG pin is to allow external gain ad-
justment for the RxO pin. If RxG is left open, then the output
signal at RxO will be inverted and output at RxO. Thus the
push–pull gain to a load from RxO to RxO is two times the
output level at RxO. If external resistors are applied from
RxO to RxG (RI) and from RxG to RxO (RG), the gain of RxO
can be set differently from inverting unity. These resistors
should be in the range of 10 kΩ. The RxO output level is un-
changed by the resistors and the RxO gain is approximately
equal to minus RG/RI. The actual gain is determined by tak-
ing into account the internal resistors which will be in parallel
to these external resistors. The internal resistors have a
large tolerance, but they match each other very closely. This
matching tends to minimize the effects of their tolerance on
external gain configurations. The circuit for RxG and RxO is
shown in the block diagram.
Txl
Transmit Analog Input
TxI is the input to the transmit filter. It is also the output of
the transmit gain amplifiers of the MC145501/02/03/05. The
input impedance is greater than 100 kΩ to VAG in the
MC145500. The TxI input has an internal gain of 1.0, such
that a +3 dBm0 signal at TxI corresponds to the peak con-
verter reference voltage as described in the Vref and RSI pin
descriptions. For 3.15 V reference, the + 3 dBm0 input
should be 6.3 V peak–to–peak.
+Tx / –Tx
Positive Tx Amplifier Input (MC145502/03/05 Only) /
Negative Tx Amplifier Input (MC145501/02/03/05 Only)
The Txl pin is the input to the transmit band–pass filter. If
+Tx or –Tx is available, then there is an internal amplifier
preceding the filter whose pins are +Tx, –Tx, and TxI. These
pins allow access to the amplifier terminals to tailor the input
gain with external resistors. The resistors should be in the
range of 10 kΩ. If +Tx is not available, it is internally tied to
VAG. If –Tx and +Tx are not available, the TxI is a unity gain
high–impedance input.
POWER SUPPLIES
VDD
Most Positive Power Supply
VDD is typically 5 to 12 V.
VSS
Most Negative Power Supply
VSS is typically 10 to 12 V negative of VDD.
For a ± 5 V dual–supply system, the typical power supply
configuration is VDD = + 5 V, VSS = – 5 V, VLS = 0 V (digital
ground accommodating TTL logic levels), and VAG = 0 V
being tied to system analog ground.
For single–supply applications, typical power supply con-
figurations include:
VDD = 10 V to 12 V
VSS = 0 V
VAG generates a mid supply voltage for referencing all
analog signals.
VLS controls the logic levels. This pin should be connected
to VDD for CMOS logic levels from VSS to VDD. This pin
should be connected to digital ground for true TTL logic
levels referenced to VLS.
TESTING CONSIDERATIONS (MC145500/01/02 ONLY)
An analog test mode is activated by connecting MSI and
CCI to 128 kHz. In this mode, the input of the A/D (the output
of the Tx filter) is available at the PDI pin. This input is direct
coupled to the A/D side of the codec. The A/D is a differential
design. This results in the gain of this input being effectively
attenuated by half. If monitored with a high–impedance buff-
er, the output of the Tx low–pass filter can also be measured
at the PDI pin. This test mode allows independent evaluation
of the transmit low–pass filter and A/D side of the codec. The
transmit and receive channels of these devices are tested
with the codec–filter fully functional.
MOTOROLA
MC145500•MC145501•MC145502•MC145503•MC145505
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