Rev. 2.0
5/2011
Page 9 of 16
V•I CHIP CORP. (A VICOR COMPANY) 25 FRONTAGE RD. ANDOVER, MA 01810 800-735-6200
vicorpower.com
040 025A00xEH48VTM
7.0 USING THE CONTROL SIGNALS VC, PC, TM, IM
The VTM Control (VC) pin is an input pin which powers the
internal VCC circuitry when within the specified voltage range
of 12 V to 16.5 V. This voltage is required in order for the VTM
module to start, and must be applied as long as the input is
below 26 V. In order to ensure a proper start, the slew rate of
the applied voltage must be within the specified range.
Some additional notes on the using the VC pin:
• In most applications, the VTM™ module will be powered
by an upstream PRM which provides a 10 ms VC pulse
during startup. In these applications the VC pins of the PRM
and VTM should be tied together.
• The VC voltage can be applied indefinitely allowing for
continuous operation down to 0 VIN.
• 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 module.
Primary Control (PC) pin can be used to accomplish the
following functions:
• Delayed start: Upon the application of VC, the PC pin will
source a constant 100 µA current to the internal RC
network. Adding an external capacitor will allow further
delay in reaching the 2.5 V threshold for module start.
• Auxiliary voltage source: Once enabled in regular
operational conditions (no fault), each VTM PC provides a
regulated 5 V, 2 mA voltage source.
• Output disable: PC pin can be actively pulled down in order
to disable the module. Pull down impedance shall be lower
than 400 Ω.
• Fault detection flag: The PC 5 V 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.
• 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:
• 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.
• 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.
Current Monitor (IM) pin provides a voltage proportional to
the output current of the VTM module. The nominal voltage
will vary between 0.2 V and 1.39 V over the output current
range of the module (See Figures 8–10). The accuracy of the
IM pin will be within 25% under all line and temperature
conditions between 50% and 100% load.
8.0 STARTUP BEHAVIOR
Depending on the sequencing of the VC with respect to the
input voltage, the behavior during startup will vary as follows:
•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 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 26 V, the
VTM module may shut down.
• Stand Alone Operation (VC applied after VIN): In this case the
module output will begin to rise upon the application of the
VC voltage (See Figure 14). The Adaptive Soft Start circuit
(See Section 10) may vary the ouput rate of rise in order to
limit the inrush current to it’s maximum level. When starting
into high capacitance, or a short, the output current will be
limited for a maximum of 900 µsec. After this period, the
adaptive soft start circuit will time out and the 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 4000 µF in this mode of operation
to ensure a sucessful start.
9.0 THERMAL CONSIDERATIONS
V•I 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 VTM48EH040T025A00 case to less than 100ºC will
keep all junctions within the V•I Chip below 125ºC for most
applications.
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.
It is not recommended to use a V•I Chip module for an
extended period of time at full load without proper heat
sinking.