MAX4890 Maxim, MAX4890 Datasheet - Page 9

• Manufacturer Part Number: MAX4890
• Description: The MAX4890/MAX4891/MAX4892 high-speed analog switches meet the needs of 10/100/1000 Base-T applications
• Manufacturer: Maxim

The MAX4890/MAX4891/MAX4892 are high-speed ana-
log switches targeted for 10/100/1000 Base-T applica-
tions. In a typical application, the MAX4890/MAX4891/
MAX4892 switch the signals from two separate inter-
face transformers and connect the signals to a single
10/100/1000 Base-T Ethernet PHY (see the Typical
Operating Circuit ). This configuration simplifies docking
station design by avoiding signal reflections associated
with unterminated transmission lines in a T configura-
tion. The MAX4891 and MAX4892 also include LED
switches that allow the LED output signals to be routed
to a docking station along with the Ethernet signals.
See the Functional Diagrams.
The MAX4890/MAX4891/MAX4892 switches provide
an extremely low capacitance and on-resistance
to meet Ethernet insertion and return-loss specifica-
tions. The MAX4891/MAX4892 feature one and three
built-in LED switches, respectively.
The MAX4890/MAX4891/MAX4892 incorporate a unique
architecture design utilizing only n-channel switches
Figure 3. Single-Ended Bandwidth, Crosstalk and Off-Isolation
10/100/1000 Base-T Ethernet LAN Switch
_______________________________________________________________________________________
Detailed Description
ANALYZER
NETWORK
ANALYZER
NETWORK
NETWORK
ANALYZER
NETWORK
ANALYZER
SINGLE-ENDED BANDWIDTH
SINGLE-ENDED CROSSTALK
SINGLE-ENDED OFF-ISOLATION
50Ω TRACE
50Ω TRACE
50Ω TRACE
49.9Ω
50Ω TRACE
R15
A0
36
A3
3
A2
2
A4
7
MAX4892
36 TQFN
0B1
31
2B1
26
4B1
22
3B1
25
within the main Ethernet switch, reducing I/O capaci-
tance 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
throughout the input signal range. An internal bandgap
reference set to 1.23V and an internal oscillator running
at 2.5MHz provide proper charge-pump operation.
Unlike other charge-pump circuits, the MAX4890/
MAX4891/MAX4892 include internal flyback capacitors,
reducing design time, board space, and cost.
The MAX4890/MAX4891/MAX4892 provide a single
digital control SEL. SEL controls the switches as well as
the LED switches as shown in Table 1.
Table 1. Truth Table
SEL
0
1
49.9Ω
49.9Ω
R14
R13
50Ω TRACE
50Ω TRACE
Test Circuits (continued)
A_ to _B1, LED_ to _LED1
A_ to _B2, LED_ to _LED2
NETWORK
ANALYZER
ANALYZER
NETWORK
CONNECTION
Digital Control Inputs
ON
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