EV8680 Datasheet, PDF (13/39 Pages) CML Microcircuits – Evaluation Kit

Evaluation Kit for CMX868
EV8680
1.6 Detailed Description
1.6.1 Hardware Description
1.6.1.1 Operating Voltage
The operating voltage (VDD) is set to 5.0V. This may be altered by changing components R22 and
R23 which are socketed. To select 2.7 Volts set R22 = 180Ω and R23 = 100Ω. The formula for
calculating the values of R22 and R23 is as follows:
240 (VDD − 1.25)
R22 + R23=
1.25
Where 240 is the value of R21 in ohms and VDD is the required supply voltage.
1.6.1.2 IDD Measurement
The evaluation device IDD may be measured by removing jumper JP3 and replacing it with a
multimeter.
1.6.1.3 Clock/Oscillator
The CMX868 may use either an external clock or its own crystal oscillator. An 11.0592MHz crystal is
provided on-board for the latter method. Two jumpers JP1 and JP2, which are normally fitted, select
the crystal oscillator. An external clock may be supplied to JP1 pin 2 once the jumpers have been
removed.
The PIC µC is provided with an on-board 4MHz crystal, X2. Note that PICs programmed by CML are
only configured for use with the on-board 4MHz crystal.
1.6.1.4 Line Interface
The majority of the line interface components are fitted in sockets for adjustment purposes. These
values should be calculated based on the operating voltage and line conditions, see the CMX868 data
sheet and ETAL transformer recommendations for more information. The 2-wire ac line impedance
matching is provided by components C2, C4, R6, T1, C5, C8, R12 and R14 which are factory fitted to
suit a 600Ω line.
A gyrator circuit is provided to allow the evaluation kit to be used with a line simulator. This circuit will
draw dc loop current in the off-hook state. The current drawn may be altered by adjusting the value of
R7. Note, the gyrator is designed to function with a dc current limited line.
1.6.1.5 Ring Detection
Ring Detection is provided by an opto-isolated circuit formed by components C1, D3 - D5, R5, R9 and
U2. The response time is set by components R10 and C6. See CMX868 data sheet for further
details.
© 2000 Consumer Microcircuits Limited
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UM8680/2