+IN/-IN DC Voltage Ports
The VTM input should not exceed the maximum specified. Be aware of
this limit in applications where the VTM is being driven above its
nominal output voltage. If less than 26 Vdc is present at the +In and -In
ports, a continuous VC voltage must be applied for the VTM to process
power. Otherwise VC voltage need only be applied for 10 ms after the
voltage at the +In and -In ports has reached or exceeded 26 Vdc. If the
input voltage exceeds the overvoltage turn-off, the VTM will shutdown.
The VTM does not have internal input reverse polarity protection.
Adding a properly sized diode in series with the positive input or a
fused reverse-shunt diode will provide reverse polarity protection.
TM – For Factory Use Only
VC – VTM Control
The VC port is multiplexed. It receives the initial VCC voltage from an
upstream PRM, synchronizing the output rise of the VTM with the
output rise of the PRM. Additionally, the VC port provides feedback to
the PRM to compensate for the VTM output resistance. In typical
applications using VTMs powered from PRMs, the PRM’s VC port
should be connected to the VTM VC port.
In applications where a VTM is being used without a PRM, 14 V must
be supplied to the VC port for as long as the input voltage is below 26 V
and for 10 ms after the input voltage has reached or exceeded 26 V. The
VTM is not designed for extended operation below 26 V. The VC port
should only be used to provide VCC voltage to the VTM during startup.
PC – Primary Control
The Primary Control (PC) port is a multifunction port for controlling the
VTM as follows:
Disable – If PC is left floating, the VTM output is enabled. To
disable the output, the PC port must be pulled lower than 2.4 V,
referenced to -In. Optocouplers, open collector transistors or relays
can be used to control the PC port. Once disabled, 14 V must be
re-applied to the VC port to restart the VTM.
Primary Auxiliary Supply – The PC port can source up to 2.4 mA
at 5 Vdc.
Figure 9—VTM pin configuration
+OUT/-OUT DC Voltage Output Ports
The output and output return are through two sets of contact
locations. The respective +Out and –Out groups must be connected in
parallel with as low an interconnect resistance as possible. Within the
specified input voltage range, the Level 1 DC behavioral model shown
in Figure 17 defines the output voltage of the VTM. The current source
capability of the VTM is shown in the specification table.
To take full advantage of the VTM, the user should note the low output
impedance of the device. The low output impedance provides fast
transient response without the need for bulk POL capacitance. Limited-
life electrolytic capacitors required with conventional converters can be
reduced or even eliminated, saving cost and valuable board real estate.
V•I Chip Voltage Transformation Module
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