MAX4529 Maxim, MAX4529 Datasheet - Page 9

• Manufacturer Part Number: MAX4529
• Description: The MAX4529 is a low-voltage T-switch designed for switching RF and video signals from DC to 300MHz in 50Ω and 75Ω systems
• Manufacturer: Maxim

The MAX4529 is designed for operation from single
+5V or dual ±5V supplies. As V+ is increased above
5V, the logic-level threshold voltage increases and the
supply current increases. In addition, if the logic levels
are not driven rail-to-rail, the analog signal pins, COM
and NC, can conduct a significant DC current (up to
1mA) to the supply pins. This current can add an
unwanted DC bias to the signal. Therefore, when oper-
ating V+ above 5V, always drive the IN pin rail-to-rail.
When power to the MAX4529 is off (i.e., V+ = 0V and V-
= 0V), the Absolute Maximum Ratings still apply. This
means that neither logic-level inputs on IN nor signals
on COM or NC can exceed ±0.3V. Voltages beyond
±0.3V cause the internal ESD-protection diodes to con-
duct, and the parts can be damaged if excessive cur-
rent flows.
Satisfactory high-frequency operation requires that
careful consideration be given to grounding. For most
applications, a ground plane is strongly recom-
mended, and GND should be connected to it with
solid copper.
In systems that have separate digital and analog (sig-
nal) grounds, connect these switch GND pins to analog
ground. Preserving a good signal ground is much more
important than preserving a digital ground. Ground cur-
rent is only a few nanoamps.
The logic-level input, IN, has voltage thresholds deter-
mined by V+ and GND. (V- does not influence the
logic-level threshold.) With +5V and 0V applied to V+
and GND, the threshold is about 1.6V, ensuring com-
patibility with TTL- and CMOS-logic drivers.
The GND pin can be connected to separate voltage
potentials if the logic-level input is not a normal logic
signal. (The GND voltage cannot exceed (V+ - 2V) or V-.)
Elevating GND reduces off isolation. Note, however,
that IN can be driven more negative than GND, as far
as V-. GND does not have to be removed from 0V when
IN is driven from bipolar sources, but the voltage on IN
should never exceed V-. GND should be separated
from 0V only if the logic-level threshold has to be
changed.
If the GND pin is not connected to 0V, it should be
bypassed to the ground plane with a surface-mount
10nF capacitor to maintain good RF grounding. DC
current in the IN and GND pins is less than 1nA, but
increases with switching frequency.
_______________________________________________________________________________________
Single-Supply Operation Above 5V
DC Ground Considerations
Grounding
Power Off
Low-Voltage, Bidirectional
A ground plane is mandatory for satisfactory high-
frequency operation. (Prototyping using hand wiring
or wire-wrap boards is strongly discouraged.) Connect
any 0V GND pins to the ground plane with solid cop-
per. (The GND pin extends the high-frequency ground
through the package wire-frame, into the silicon itself,
thus improving isolation.) The ground plane should be
solid metal underneath the device, without interrup-
tions. There should be no traces under the device itself.
For DIP packages, this applies to both sides of a two-
sided board. Failure to observe this will have a minimal
effect on the “on” characteristics of the switch at high
frequencies, but it will degrade the off isolation and
crosstalk.
V+ and V- pins should be bypassed to the ground
plane with surface-mount 10nF capacitors. For DIP
packages, they should be mounted as close as possi-
ble to the pins on the same side of the board as the
device. Do not use feedthroughs or vias for bypass
capacitors. For surface-mount packages, the pins are
so close to each other that the bypass capacitors
should be mounted on the opposite side of the board
from the device. In this case, use short feedthroughs or
vias, directly under the V+ and V- pins. Any GND pin
not connected to 0V should be similarly bypassed. If V-
is 0V, connect it directly to the ground plane with solid
copper. Keep all leads short.
Keep all signal leads as short as possible. Separate all
signal leads from each other and other traces with the
ground plane on both sides of the board. Where possi-
ble, use coaxial cable instead of printed circuit board
traces.
IC sockets degrade high-frequency performance and
should not be used if signal bandwidth exceeds 5MHz.
Surface-mount parts, having shorter internal lead
frames, provide the best high-frequency performance.
Keep all bypass capacitors close to the device, and
separate all signal leads with ground planes. Such
grounds tend to be wedge-shaped as they get closer to
the device. Use vias to connect the ground planes on
each side of the board, and place the vias in the apex of
the wedge-shaped grounds that separate signal leads.
Logic-level signal lead placement is not critical.
RF/Video Switch
AC Ground and Bypassing
Signal Routing
Board Layout
9