LTM8047
6
8047fc
For more information www.linear.com/LTM8047
PIN FUNCTIONS
V
OUT
(Bank 1): V
OUT
and V
OUT
–
comprise the isolated
output of the LTM8047 flyback stage. Apply an external
capacitor between V
OUT
and V
OUT
–
. Do not allow V
OUT
–
to
exceed V
OUT
.
V
OUT
–
(Bank 2): V
OUT
–
is the return for V
OUT
. V
OUT
and
V
OUT
–
comprise the isolated output of the LTM8047. In
most applications, the bulk of the heat flow out of the
LTM8047 is through the GND and V
OUT
–
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. Apply an external
capacitor between V
OUT
and V
OUT
–
.
GND (Bank 4): This is the primary side local ground of the
LTM8047 primary. In most applications, the bulk of the heat
flow out of the LTM8047 is through the GND and V
OUT
–
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.
V
IN
(Bank 3): V
IN
supplies current to the LTM8047’s inter-
nal regulator and to the integrated power switch. These
pins must be locally bypassed with an external, low ESR
capacitor.
RUN (Pin F3):
A resistive divider connected to V
IN
and this
pin programs the minimum voltage at which the LTM8047
will operate. Below 1.24V, the LTM8047 does not deliver
power to the secondary. Above 1.24V, power will be de
-
livered to the secondary and 10µA will be fed into the SS
pin. When RUN is less than 1.24V, the pin draws 2.5µA,
allowing for a programmable hysteresis. Do not allow a
negative voltage (relative to GND) on this pin.
ADJ (Pin G7): Apply a resistor from this pin to GND to set
the output voltage, using the recommended value given
in Table 1. If Table 1 does not list the desired V
OUT
value,
the equation
R
ADJ
= 28.4 V
OUT
–0.879
(
)
kΩ
may be used to approximate the value. To the seasoned
designer, this exponential equation may seem unusual.
The equation is exponential due to non-linear current
sources that are used to temperature compensate the
output regulation.
BIAS (Pin H5): This pin supplies the power necessary to
operate the LTM8047. It must be locally bypassed with a
low ESR capacitor of at least 4.7μF. Do not allow this pin
voltage to rise above V
IN
.
SS (Pin H6): Place a soft-start capacitor here to limit inrush
current and the output voltage ramp rate. Do not allow a
negative voltage (relative to GND) on this pin.
