MAX4927 Maxim, MAX4927 Datasheet - Page 7

• Manufacturer Part Number: MAX4927
• Description: The MAX4927 meets the needs of high-speed differential switching, including that of Gigabit Ethernet (10/100/1000) Base-T switching as well as LVDS and LVPECL switching
• Manufacturer: Maxim

The MAX4927 is a high-speed analog switch targeted
for 1000 Base-T applications. In a typical application,
the MAX4927 switches the signals from two separate
interface transformers and connects 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 unterminated transmission lines in a T configura-
tion. The MAX4927 is protected against ±15kV electro-
static discharge (ESD) events. The MAX4927 also
includes LED switches that allow the LED output sig-
nals to be routed to a docking station along with the
Ethernet signals. See the Functional Diagrams.
With its low resistance and capacitance, as well as high
ESD protection, the MAX4927 can be used to switch
most low-voltage differential signals, such as LVDS,
SERDES, and LVPECL, as long as the signals do not
exceed maximum ratings of the device.
The MAX4927 switch provides an extremely low capac-
itance and on-resistance to meet Ethernet insertion and
return-loss specifications. The MAX4927 features three
built-in LED switches.
The MAX4927 incorporates a unique architecture design
utilizing only n-channel switches within the main Ethernet
switch, reducing I/O capacitance and channel resis-
tance. An internal two-stage charge pump with a nomi-
nal 7.5V output provides the high voltage needed to
drive the gates of the n-channel switches while maintain-
ing a consistently low R
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 cir-
cuits, the MAX4927 includes internal flyback capacitors,
reducing design time, board space, and cost.
The MAX4927 provides a single digital control input,
SEL. SEL controls the high-frequency switches as well
as the LED switches as shown in Table 1.
PIN
EP
51
52
54
1000 Base-T, ±15kV ESD Protection LAN Switch
_______________________________________________________________________________________
NAME
2LED2
2LED1
LED2
EP
Detailed Description
ON
Digital Control Inputs
throughout the input signal
2LED2 Output. Drive SEL high (SEL = 1) to connect LED2 to 2LED2.
2LED1 Output. Drive SEL low (SEL = 0) to connect LED2 to 2LED1.
LED2 Input
Exposed Paddle. Connect EP to GND or leave EP unconnected.
The on-resistance of the MAX4927 is very low and sta-
ble as the analog input signals are swept from ground
to V
switches are bidirectional, allowing A_ and _B_ to be
configured as either inputs or outputs.
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges encountered during handling and
assembly. All the high-frequency switch inputs (A_,
_B_), LED switch inputs (LED_, _LED_), and SEL have
high ESD protection against static electricity. Maxim’s
engineers have developed state-of-the-art structures to
protect these pins against ESD of ±15kV without dam-
age. After an ESD event, the MAX4927 keeps working
without latchup or damage.
ESD protection can be tested in various ways. All signal
and control inputs of the MAX4927 are characterized
for protection to the following limits:
•
•
•
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, test methodology, and test results.
Table 1. Truth Table
±15kV using the Human Body Model
±8kV using the Contact Discharge Method specified
in IEC 61000-4-2
±15kV using the Air-Gap Discharge Method specified
in IEC 61000-4-2
DD
SEL
0
1
FUNCTION
(see the Typical Operating Characteristics). The
Pin Description (continued)
A_ to _B1, LED_ to _LED1
A_ to _B2, LED_ to _LED2
±15kV ESD Protection
CONNECTION
Analog Signal Levels
ESD Test Conditions
7