ICS1894-40
10BASE-T/100BASE-TX INTEGRATED PHYCEIVER WITH RMII INTERFACE
PHYCEIVER
If a crystal is used as the clocking source, connect it to both
the REF_IN (pin 37) and REF_OUT (pin 36) pins of the
ICS1894-40. A pair of bypass capacitors on either side of
the crystal are connected to ground. The crystal is used in
the parallel resonance or anti-resonance mode. The value
of the load caps serve to adjust the final frequency of the
crystal oscillation. Typical applications would use 25 pF load
caps. The exact value will be affected by the board routing
capacitance on REF_IN and REF_OUT pins. Smaller load
capacitors raise the frequency of oscillation.
Once the exact value of load capacitance is established it
will be the same for all boards using the same specification
crystal. The best way to measure the crystal frequency is to
measure the frequency of TXCLK (pin 28) using a frequency
counter with a 1 second gate time. Using the buffered output
TXCLK prevents the crystal frequency from being affected
by the measurement. The crystal specification is shown in
the 25MHz Crystal Specification table.
25 MHz Crystal Specification Table
Specifications
Symbol Minimum
Typical Maximum
Unit
MHz
ppm
pF
Fundamental Frequency
Freq. Tolerance
F0
24.99875 25.00000 25.00125
ΔF/f
Cin
50
Input Capacitance
3
25 MHz Oscillator Specification table
Specifications
Symbol Minimum
Typical Maximum
Unit
MHz
ppm
%
Output Frequency
F0
24.99875 25.00000 25.00125
50
Freq. Stability (including aging)
ΔF/f
Tw/T
Duty cycle CMOS level one-half VDD
35
65
VIH
VIL
2.79
Volts
Volts
0.33
50 MHz Oscillator Specification table
Specifications
Symbol Minimum
Typical Maximum
Unit
MHz
ppm
%
Output Frequency
F0
49.9975 50.00000
50.0025
50
Freq. Stability (including aging)
ΔF/f
Duty cycle CMOS level one-half VDD
Tw/T
35
65
VIH
VIL
2.79
Volts
Volts
0.33
Status Interface
The ICS1894-40 has five multi-function configuration pins
that report the PHY status by providing signals that are
intended for driving LEDs. Configuration is set by Bank0
Register 20.
IDT® 10BASE-T/100BASE-TX INTEGRATED PHYCEIVER WITH RMII INTERFACE
14
ICS1894-40
REV G 060110
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
