LTM8045
9
8045fc
For more information www.linear.com/LTM8045
pin FuncTions
V
OUT
–
(Bank 1): V
OUT
–
is the negative output of the
LTM8045. Apply an external capacitor between V
OUT
+
and
V
OUT
–
. Tie this net to GND to configure the LTM8045 as
a positive output SEPIC regulator.
V
OUT
+
(Bank 2): V
OUT
+
is the positive output of the
LTM8045. Apply an external capacitor between V
OUT
+
and
V
OUT
–
. Tie this net to GND to configure the LTM8045 as
a negative output inverting regulator.
GND (Bank 3): Tie these GND pins to a local ground plane
below the LTM8045 and the circuit components. GND
MUST BE CONNECTED EITHER TO V
OUT
+
OR V
OUT
–
FOR
PROPER OPERATION. In most applications, the bulk of
the heat flow out of the LTM8045 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
FB
) to this net.
V
IN
(Bank 4): The V
IN
pin supplies current to the LTM8045’s
internal regulator and to the internal power switch. This
pin must be locally bypassed with an external, low ESR
capacitor.
FB (Pin A3):
If configured as a SEPIC, the LTM8045
regulates
its FB pin to 1.215V. Apply a resistor between
FB and V
OUT
+
. Its value should be R
FB
= [(V
OUT
– 1.215)/
0.0833]kΩ. If
the LTM8045 is configured as an inverting
converter, the LTM8045 regulates the FB pin to 5mV. Apply
a resistor between FB and V
OUT
–
of value R
FB
= [(|V
OUT
|
+ 0.005)/0.0833]kΩ.
SYNC (Pin E1): To synchronize the switching frequency
to an outside clock, simply drive this pin with a clock. The
high voltage level of the clock needs to exceed 1.3V, and
the low level should be less than 0.4V. Drive this pin to
less than 0.4V to revert to the internal free running clock.
Ground this pin if the SYNC function is not used. See the
Applications Information section for more information.
SS (Pin F1): Place a soft-start capacitor here. Upon start-up,
the SS pin will be charged by a (nominally) 275k resistor
to about 2.2V.
RT (Pin G1): The RT pin is used to program the switching
frequency of the LTM8045 by connecting a resistor from
this pin to ground. The necessary resistor value for the
LTM8045 is determined by the
equation R
T
= (91.9/f
OSC
) – 1,
where f
OSC
is the typical switching frequency in MHz and
R
T
is in kΩ. Do not leave this pin open.
RUN (Pin G3): This pin is used to enable/disable the chip
and restart the soft-start sequence. Drive below 1.235V
to disable the chip. Drive above 1.385V to activate chip
and restart the soft-start sequence. Do not float this pin.
