VTM48Ex480y006A00
Using the Control Signals VC, PC, TM
Start Up Behavior
The VTM Control (VC) pin is an input pin which powers the
internal VCC circuitry when within the specified voltage range of
11.5V to 16.5V. This voltage is required for VTM current multiplier
start up and must be applied as long as the input is below 26V. In
order to ensure a proper start, the slew rate of the applied voltage
must be within the specified range.
Depending on the sequencing of the VC with respect to the input
voltage, the behavior during start up will vary as follows:
n■Normal operation (VC applied prior to Vin): In this case the
controller is active prior to ramping the input. When the input
voltage is applied, the VTM module output voltage will track
the input (See Figure 13). The inrush current is determined by
the input voltage rate of rise and output capacitance. If the VC
voltage is removed prior to the input reaching 26V, the VTM may
shut down.
Some additional notes on the using the VC pin:
n■In most applications, the VTM module will be powered by an
upstream PRM™ regulator which provides a 10ms VC pulse
during start up. In these applications the VC pins of the PRM
regulator and VTM current multiplier should be tied together.
n■Stand-alone operation (VC applied after Vin): In this case
the VTM output will begin to rise upon the application of the VC
voltage (See Figure 14). The Adaptive Soft Start Circuit may vary
the ouput rate of rise in order to limit the inrush current to its
maximum level. When starting into high capacitance, or a short,
the output current will be limited for a maximum of 1200µs.
After this period, the Adaptive Soft Start Circuit will time out and
the VTM module may shut down. No restart will be attempted
until VC is re-applied or PC is toggled. The maximum output
capacitance is limited to 100µF in this mode of operation to
ensure a sucessful start.
n■The VC voltage can be applied indefinitely allowing for
continuous operation down to 0Vin.
n■The fault response of the VTM module is latching. A
positive edge on VC is required in order to restart the unit. If VC
is continuously applied the PC pin may be toggled to restart the
VTM module.
Primary Control (PC) pin can be used to accomplish the
following functions:
n■Delayed start: Upon the application of VC, the PC pin will
source a constant 100µA current to the internal RC network.
Adding an external capacitor will allow further delay in reaching
the 2.5V threshold for module start.
Thermal Considerations
VI Chip® products are multi-chip modules whose temperature
distribution varies greatly for each part number as well as with the
input/output conditions, thermal management and environmental
conditions. Maintaining the top of the VTM48EF480T006A00 case
to less than 100ºC will keep all junctions within the VI Chip module
below 125ºC for most applications.
n■Auxiliary voltage source: Once enabled in regular operational
conditions (no fault), each VTM PC provides a regulated 5V,
2mA voltage source.
n■Output disable: PC pin can be actively pulled down in order
to disable the module. Pull down impedance shall be lower
than 400Ω.
The percent of total heat dissipated through the top surface
versus through the J-lead is entirely dependent on the particular
mechanical and thermal environment. The heat dissipated through
the top surface is typically 60%. The heat dissipated through
the J-lead onto the PCB board surface is typically 40%. Use
100% top surface dissipation when designing for a conservative
cooling solution.
n■Fault detection flag: The PC 5V voltage source is internally
turned off as soon as a fault is detected. It is important to notice
that PC doesn’t have current sink capability. Therefore, in an
array, PC line will not be capable of disabling neighboring
modules if a fault is detected.
It is not recommended to use a VI Chip module for an extended
period of time at full load without proper heat sinking.
n■Fault reset: PC may be toggled to restart the unit if VC is
continuously applied.
Temperature Monitor (TM) pin provides a voltage proportional
to the absolute temperature of the converter control IC.
It can be used to accomplish the following functions:
n■Monitor the control IC temperature: The temperature in
Kelvin is equal to the voltage on the TM pin scaled by 100.
(i.e. 3.0 V = 300 K = 27ºC). If a heat sink is applied, TM can be
used to thermally protect the system.
n■Fault detection flag: The TM voltage source is internally turned
off as soon as a fault is detected. For system monitoring
purposes (microcontroller interface) faults are detected on falling
edges of TM signal.
VTM™ Current Multiplier
Page 11 of 19
Rev 1.4
03/2017
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