Digilent VRM - Manual (Page 2)

Digilent VRM Reference Manual
www.digilentinc.com page 2 of 2
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The input current to the regulator is a function
of the voltage ratio between input and output
voltage, output current, and regulator
efficiency. The following formula applies:
I
i
= ((V
o
/V
i
)*I
o
)/e
Where: I
i
& I
o
are input and output current,
V
i
& V
o
are input and output voltage, and e is
the regulator efficiency. The efficiency depends
on several factors, but a value of 0.9 is
reasonable. Refer to the TI data sheet for the
TPS54620 for more information.
Screw terminal connector, J1, and the three
two-pin headers of J4 provide access to the
regulated output voltage. Digilent has available
two-wire MTE power cables that are ideal for
connections to the two-pin headers. As noted
above, the screw terminal connector is rated
for up to 10A, but the two pins headers are
only rated for 2A each. Do not attempt to draw
more than 2A on these connectors as they will
get very hot and may fail.
Observe proper polarity when connecting the
outputs of the VRM to the circuit being
powered. The polarity markings for J4 are on
the top of the board near J4. The polarity
markings for J1 are on the bottom of the board.
Jumper Options
Several jumpers are used to configure or
control the operation of the Digilent VRM:
Jumper J2 is used to select the output voltage.
Install a shorting block on J2 to select 3.3V
output. Otherwise the voltage output is 5V.
Connector J5 allows access to the enable input
to the regulator. This allows an external
controller, (such as a microcontroller) to turn
the regulator on or off. Driving the EN pin on
this connector to ground will turn off the
regulator. Allowing this pin to float will turn the
regulator on. The pin can also be used to
provide an undervoltage lockout. Refer to the
data sheet for the TPS54620 for more
information.
Connector J8 can be used to provide an
external clock signal to control the switching
frequency of the regulator. Connecting the CLK
pin on J8 to an external clock will cause the
VRM’s switching supply to synchronize to the
external clock source. The external clock must
be a square wave between 200kHz and
1600kHz. The amplitude of this signal must
transition below 0.8V and above 2.0V. If the
CLK pin is left disconnected, the supply will
switch at 479kHz.
Connector J7 provides access to the PGOOD
signal out of the regulator. The PGOOD pin on
J7 provides the status of the VRM output
voltage. This pin floats during normal
operation. The pin is driven low to indicate a
power supply fault. This occurs when the
VRM’s reference voltage is below 91% or
above 109% of normal. The PGOOD pin
should be connected to a pull-up resistor to
avoid erroneous fault detection.