MAX4888A Maxim, MAX4888A Datasheet - Page 11

• Manufacturer Part Number: MAX4888A
• Description: The MAX4888A/MAX4889A high-speed passive switches route PCI Express® (PCIe) data between two possible destinations
• Manufacturer: Maxim

The MAX4888A/MAX4889A primary applications are
aimed at reallocating PCIe lanes (see Figure 5). For
example, in graphics applications, several manufacturers
have found that it is possible to improve performance by
a factor of nearly two by splitting a single 16-lane PCIe
bus into two 8-lane buses. Two of the more prominent
examples are SLI™ (Scaled Link Interface) and
CrossFire™. The MAX4889A permits a computer
motherboard to operate properly with a single 16-lane
graphics card, and can later be updated to dual cards.
The same motherboard can be used with dual cards
where the user sets a jumper or a bit through software
to switch between single- or dual-card operation.
Common mode below 1V operation requirement.
High-speed switches require proper layout and design
procedures for optimum performance. Keep design-
controlled impedance PCB traces as short as possible
or follow impedance layouts per the PCIe specification.
Ensure that power-supply bypass capacitors are
placed as close to the device as possible. Multiple
bypass capacitors are recommended. Connect all
grounds and the exposed pad to large ground planes.
Common mode below 1V operation requirement.
Figure 5. The MAX4888A/MAX4889A Used as a Single-Lane
Switch
CrossFire is a trademark of ATI Technologies, Inc.
SLI is a trademark of NVIDIA Corporation.
ONE LANE
NOTE: ONLY ONE LANE IS SHOWN FOR CLARITY
Applications Information
______________________________________________________________________________________
MAX4888A
MAX4889A
5.0Gbps PCI Express Passive Switches
A
PCIe Switching
DATA IS ROUTED
BOARD A OR B
Board Layout
DIRECTION
TO EITHER
DATA
B
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges encountered during handling and
assembly. The COM_+ and COM_- lines have extra
protection against static electricity. Maxim’s engineers
have developed state-of-the-art structures to protect
these pins against ESD of ±6kV without damage. The
ESD structures withstand ±6kV of ESD in all states: nor-
mal operation, state output mode, and powered down.
The MAX4889A COM_+ and COM_- pins are character-
ized for ±6kV ESD protection using the Human Body
Model (MIL-STD-883, Method 3015). Figure 6 shows
the Human Body Model and Figure 7 shows the current
waveform it generates when discharged into low
impedance. This model consists of a 100pF capacitor
charged to the ESD voltage of interest, which is then
discharged into the device through a resistor.
Figure 6. Human Body ESD Test Model
Figure 7. Human Body Model Current Waveform
PROCESS: CMOS
AMPERES
VOLTAGE
SOURCE
HIGH-
DC
I
P
36.8%
100%
90%
10%
CHARGE-CURRENT-
LIMIT RESISTOR
0
0
1MΩ
t
RL
R
C
100pF
C s
STORAGE
CAPACITOR
CURRENT WAVEFORM
TIME
1500Ω
RESISTANCE
DISCHARGE
R
D
Chip Information
t
DL
Human Body Model
I r
ESD Protection
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
DEVICE
UNDER
TEST
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