Vicor VI Chip VTM Evaluation Board - Manual (Page 12)

UG:014 vicorpower.com Applications Engineering: 800 927.9474 Page 12
PRM ® & VTM ® Evaluation Boards
The VTM evaluation board has been designed for compatibility with all PRM evaluation
boards to accommodate any PRM-VTM combination. The VTM evaluation board contains
dual connectors designed to mate with J10 and J13 on PRM board. An additional signal
connector shares VTM signal pins along with TM, S+ and S- to the PRM board. When
connected to a PRM evaluation board the TM signal provides feedback to the VT pin of
the PRM enabling temperature compensation in Adaptive Loop configuration.
Standalone Operation vs PRM-VTM Operation
In standalone VTM operation, the VTM cannot self-start with only an input voltage
applied. A voltage of 14 V must be applied to its VC pin or test point for it to become
active. Ensure that the applied VC slew rate is within the specified limits of the device.
The VC voltage may be removed once the VTM has started and the input voltage has
reached 26 V or VC can be applied continuously to allow operation down below 26 V
input voltage. When connected together, the PRM provides power and the VC pulse via
the J14 connector to the VTM. A 22uF,100 V electrolytic input capacitor is provided with
the board and is recommended in standalone VTM operation.
Refer to the VI Chip PRM evaluation board
UG:013 for more information on various
modes of PRM+VTM operation.
PRM-VTM Non-Isolated Remote Sense
To demonstrate non-isolated remote sense with a PRM evaluation board, the VTM
isolation must be broken by tying VTM -IN to –OUT. This can be done using sockets on
both side of R19 resistor footprint or by soldering a 2512 zero ohm resistor at the R19
location. Output sense test points are routed to connector J11 and provide feedback to the
PRM remote sense circuitry. By default, the +S and –S pins are connected to the output
pins of VTM through local sense resistors. To demonstrate sensing at a remote point of
load, the local sense resistors can be bypassed by connecting the +S and –S test points to
the desired sense location. Use a twisted pair to avoid noise pickup.
It is recommended to use a network analyzer to measure the closed loop frequency
response when adjusting compensation. The VTM boards provide test points which can
be used to inject the network analyzer AC signal and measure the closed loop response.
For PRM-VTM Remote Sense mode, test points are provided on the VTM board in series
with the +S connections (Labeled “RS Sig Inj +/-“) and should be used.
Figure 5.
PRM evaluation board
connection to
VTM evaluation board