External Supply - Keysight Technologies 34945A Configuration Manual

14 | Keysight | 34945A, L4445A, and L4490A/L4491A - Configuration Guide

External supply

Each 34945EXT module is limited to 2 A
continuous current from an externally
connected power supply (4.75 V to 30 V).
The actual amount of power required by
each EXT module depends on the types of
switches used.
When using an external power supply
with either the master 34945EXT module
or slave 34945EXT modules (required),
the supply must be able to provide the
quiescent current requirement of the EXT
modules, plus the quiescent and switching
currents of the switches themselves.
The power requirement of the 34945EXT
is 1.2 W. For supported external supply
voltages of 24 V, 12 V, and 5 V, the current
required for a single EXT module is as
follows:
current = power / voltage
24 V: 1.2 W / 24 V = 50 mA
12 V: 1.2 W / 12 V = 100 mA
5 V: 1.2 W / 5 V = 240 mA
If multiple 34945EXT modules are driven
by a single external supply, the power
required from the supply increases by
1.2 W for each EXT module present. Thus,
if two EXT modules are driven by a single
supply, the power value in the equations
becomes 2.4 W – doubling the current
requirement.
Remember that the external supply must
also meet the quiescent and switching
current requirements of the switch. Using
the Keysight 87104/87106A, B, C coaxial
switches from the internal supply example,
the switch specifications again are:
Supply current (switching: pulse width =15 ms:Vcc = 24 VDC): 200 mA Nom
Supply current (quiescent): 50 mA Max
The quiescent current required for the
34945EXT module is:
[34945EXT quiescent current from 24 V]
[24 V: 1.2 W / 24 V = 50 mA]
Therefore, the current required from an
external supply for actuating a single
87104/87106 switch on a single 34945EXT
module is:
[34945EXT quiescent current from 24 V] + [switch quiescent current] + [switching current]
[24 V: 1.2 W / 24 V = 50 mA]
= 300 mA (15 ms pulse, 100 mA quiescent)
In summary, when using an external
supply, the current calculations must
include the quiescent current requirement
of the 34945EXT and the quiescent
current requirement of each switch. These
quantities are then added to the switching
(pulse) current requirement of the device.
+ [50 mA] +
www.keysight.com/find/34980a
[200 mA]