Datasheet
MAX4890E/MAX4892E
1000 Base-T, ±15kV ESD Protection LAN Switches
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Detailed Description
The MAX4890E/MAX4892E are high-speed analog
switches targeted for 1000 Base-T applications. In a
typical application, the MAX4890E/MAX4892E switch
the signals from two separate interface transformers
and connect the signals to a single 1000 Base-T
Ethernet PHY (see the Typical Operating Circuit). This
configuration simplifies docking station design by
avoiding signal reflections associated with unterminat-
ed transmission lines in a T configuration. The
MAX4890E/MAX4892E are protected against ±15kV
electrostatic discharge (ESD) shocks. The MAX4892E
also includes LED switches that allow the LED output
signals to be routed to a docking station along with the
Ethernet signals. See the Functional Diagrams.
With their low resistance and capacitance, as well as
high ESD protection, the MAX4890E/MAX4892E can be
used to switch most low-voltage differential signals,
such as LVDS, SEREDES, and LVPECL, as long as the
signals do not exceed maximum ratings of the devices.
The MAX4890E/MAX4892E switches provide an
extremely low capacitance and on-resistance to meet
Ethernet insertion and return-loss specifications. The
MAX4892E features three built-in LED switches.
The MAX4890E/MAX4892E incorporate a unique archi-
tecture design utilizing only n-channel switches within
the main Ethernet switch, reducing I/O capacitance and
channel resistance. An internal two-stage charge pump
with a nominal output of 7.5V provides the high voltage
needed to drive the gates of the n-channel switches
while maintaining a consistently low R
ON
throughout the
input signal range. An internal bandgap reference set to
1.23V and an internal oscillator running at 2.5MHz pro-
vide proper charge-pump operation. Unlike other
charge-pump circuits, the MAX4890E/MAX4892E
include internal flyback capacitors, reducing design
time, board space, and cost.
R15
49.9Ω
NETWORK
ANALYZER
NETWORK
ANALYZER
NETWORK
ANALYZER
NETWORK
ANALYZER
SINGLE-ENDED BANDWIDTH
50Ω TRACE
SINGLE-ENDED CROSSTALK
50Ω TRACE
SINGLE-ENDED OFF-ISOLATION
50Ω TRACE
50Ω TRACE
A0
36
A2
2
A3
3
A4
7
4B1
22
3B1
25
2B1
26
0B1
31
50Ω TRACE
NETWORK
ANALYZER
NETWORK
ANALYZER
50Ω TRACE
R14
49.9Ω
R13
49.9Ω
MAX4892E
36 TQFN
Figure 1. Single-Ended Bandwidth, Crosstalk, and Off-Isolation