Vicor VI Chip Remote Sense PRM Evaluation Board - Manual (Page 23)

UG:016 vicorpower.com Applications Engineering: 800 927.9474 Page 23
In this configuration, the PRM ® and VTM ® evaluation boards are connected together to
form a PRM / VTM pair and regulation is performed at the VTM module output. The
+SENSE and -SENSE connections are made at the VTM output through connector J10.
This is a non-isolated configuration and therefore the VTM isolation must be broken
by tying the VTM -OUT and VTM -IN pins together. The VTM evaluation board has
provisions for easily breaking the isolation. U11B is configured as a differential amplifier
with gain set for appropriate output voltage. R33 and R41 set the gain. POT R44 can be
used to set the required voltage at the VTM output. Maximum output voltage can be set
for maximum 1.25 V reference voltage. R33 and R41 is calculated
using following equation.
Where: V
OUT_SET (MAX)
is the maximum VTM output trim voltage
Please note that R33 and R41 are not populated by default. Sockets can be used to
populate through-hole resistors R33 and R41.
In order to configure the evaluation boards for non-isolated remote sense the following
steps must be taken:
1.
Connect the PRM and VTM evaluation boards together
2. Configure the operating mode switch as described
3. Break the isolation by connecting VTM-IN and -OUT together
4. Calculate and install the appropropriate differential sense resistors (R33 and R41)
5. Install compensation components C20 and R28
Remote Sense Compensation Components
By default, compensation components are not populated, and are required for
operation. Please note that board comes with default through-hole compensation
components C20 and R28 that can be used to get a baseline for Remote Sense operation.
Sockets can be used for easy installation of C20 and R28. These components are not
optimized and will have low bandwidth response. Transient response can be improved
by adjusting the compensation components as outlined in the PRM datasheet.
It is recommended to use a network analyzer to measure the closed loop frequency
response when adjusting compensation. The PRM and VTM boards provide test points
which can be used to inject the network analyzer AC signal and measure the
closed loop response.
For PRM Remote Sense mode (single ended local sense), test points TP37/TP38 and H46/
H45 are in series between the PRM +OUT and the voltage sense resistors and
should be used.
For PRM-VTM Remote Sense mode (differential sense) test points are provided on the
VTM board in series with the +S connections (Labeled “AC Sig Inj +/-“) and
should be used.
Trim and Soft-start Adjustment in Remote Sense Operation
Trim and soft start adjustment in Remote Sense Operation is set by the reference voltage
network shown below. The PRM evaluation board is normally configured for a 20 V to
55 V trim range. Trim POT R44 is used to trim the output voltage in
Remote Sense Operation.
R
33
= R
41
=
V
OUT_SET (MAX)
•
1.27kΩ
1.25 V
Equation 1