Keysight Technologies L4490A, Руководство пользователя

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Keysight L4490A/L4491A User’s Guide 41
Hardware Configuration
Internal/External Power Supply Considerations
As shown in Figure 2-1, the channel drive source for switches and attenuators in
the L4490A/L4491A RF Switch Platform is provided through the internal (or
external) power supply. The internal or external supply used must meet the
quiescent (steady-state) and switching current requirements of the switches in
your application. The following sections provide additional information on these
requirements and the recommended configuration of these supplies.
Internal Supply
The master 34945EXT (Figure 2-1) and optional second 34945EXT (Option 002)
can receive their power from either the in24V supply of the
L4490A/L4491A or from an external supply. When using the in24V supply
as the channel drive source, the switching current or the switching and quiescent
currents drawn from the supply must not exceed the supply’s specification of 600
mA continuous.
If this limit is exceeded, an overcurrent condition can occur which shuts down the
internal supply. When this happens, you must remove the device/condition
causing the overcurrent and cycle power on the L4490A or L4491A. See
“Overcurrent Conditions” in Chapter 5 for more information.
The quiescent current of 34945EXTs driven by the internal supply is accounted
for by the supply rating and is not included in quiescent current and switching
current calculations. Only the specified currents (quiescent, switching) of the
switch must be considered.
As an example, the Keysight 87104/87106A, B, C coaxial switches specify the
following:
Supply current (switching: pulse width =15 ms:Vcc = 24 VDC): 200 mA Nom
Supply current (quiescent): 50 mA Max
Using the L4490A/L4491A in24V supply, the current required for
actuating a 87104/87106 switch is:
[87104 / 87106 switch quiescent current] + [87104 / 87106 switching current]
[ 50 mA ] + [ 200 mA ]
= 250 mA (15 ms pulse, 50 mA quiescent)
The combination of switches and their power requirements often make it
difficult to determine if the capacity of the L4490A and L4491A internal
+24V supply will be exceeded. If overcurrent conditions occur repeatedly
regardless of recovery time (Chapter 5), the use of an external power
supply as the channel drive source may be required.