LTM8025
8
8025fc
For more information www.linear.com/LTM8025
pin FuncTions
V
OUT
(Bank 1): Power Output Pins. Apply the output filter
capacitor and the output load between these pins and
GND pins.
GND (Bank 2): Tie these GND pins to a local ground plane
below the LTM8025 and the circuit components. In most
applications, the bulk of the heat flow out of the LTM8025
is through these pads, so the printed circuit design has a
large impact on the thermal performance of the part. See
the PCB Layout and Thermal Considerations sections for
more details. Return the feedback divider (R
ADJ
) to this net.
V
IN
(Bank 3): The V
IN
pin supplies current to the LTM8025’s
internal regulator and to the internal power switch. This
pin must be locally bypassed with an external, low ESR
capacitor; see Table 1 for recommended values.
AUX (Pin G5): Low Current Voltage Source for BIAS. In
many designs, the BIAS pin is simply connected to V
OUT
.
The AUX pin is internally connected to V
OUT
and is placed
adjacent to the BIAS pin to ease printed circuit board rout-
ing. Although this pin is internally connected to V
OUT
, it
is not intended to deliver a high current, so do not draw
current from this pin to the load. If this pin is not tied to
BIAS, leave it floating.
BIAS (Pin H5): The BIAS pin connects to the internal power
bus. Connect to a power source greater than 2.8V and less
than 25V. If the output is greater than 2.8V, connect this
pin there. If the output voltage is less, connect this to a
voltage source between 2.8V and 25V. Also, make sure
that BIAS + V
IN
is less than 56V.
RUN/SS (Pin L5): Pull the RUN/SS pin below 0.2V to
shut down the LTM8025. Tie to 2.5V or more for normal
operation. If the shutdown feature is not used, tie this pin
to the V
IN
pin. RUN/SS also provides a soft-start function;
see the Applications Information section.
SYNC (Pin L6): This is the external clock synchronization
input. Ground this pin for low ripple Burst Mode operation
at low output loads. Tie to a stable voltage source greater
than 0.7V to disable Burst Mode operation. Do not leave
this pin floating. Tie to a clock source for synchroniza
-
tion. Clock edges should have rise and fall times faster
than 1μs. See the Synchronization section in Applications
Information.
RT (Pin G7):
The RT pin is used to program the switching
frequency of the LTM8025 by connecting a resistor from
this pin to ground. Table 2 gives the resistor values that
correspond to the resultant switching frequency. Minimize
the capacitance at this pin.
SHARE (Pin H7): Tie this to the SHARE pin of another
LTM8025 when paralleling the outputs. Otherwise, do
not connect.
PGOOD (Pin J7): The PGOOD pin is the open-collector
output of an internal comparator. PGOOD remains low until
the ADJ pin is within 10% of the final regulation voltage.
PGOOD output is valid when V
IN
is above 3.6V and RUN/SS
is high. If this function is not used, leave this pin floating.
ADJ (Pin K7): The LTM8025 regulates its ADJ pin to 0.79V.
Connect the adjust resistor from this pin to ground. The
value of R
ADJ
is given by the equation R
ADJ
= 394.21/
(V
OUT
– 0.79), where R
ADJ
is in kΩ.
