LTM8057
8
8057f
For more information www.linear.com/LTM8057
PIN FUNCTIONS
V
OUT
(Bank 1): V
OUT
and V
OUT
–
comprise the isolated
output of the LTM8057 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 both V
OUT1
and
V
OUT2
. V
OUT1
and V
OUT
–
comprise the isolated output of
the LTM8057. In most applications, the bulk of the heat
flow out of the LTM8057 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
LTM8057 primary. In most applications, the bulk of the heat
flow out of the LTM8057 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 5): V
IN
supplies current to the LTM8057’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 LTM8057
will operate. Below 1.24V, the LTM8057 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. T
ie this pin
to V
IN
if it is not used.
ADJ (Pins G7): Apply a resistor from this pin to GND to
set the output voltage V
OUT1
relative to V
OUT
–
, 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
OUT1
–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 nonlinear current sources
that are used to temperature compensate the regulation.
BIAS (Pin H5): This pin supplies the power necessary to
operate the LTM8057. 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.
PACKAGE ROW AND COLUMN LABELING MAY VARY
AMONG µModule PRODUCTS. REVIEW EACH PACKAGE
LAYOUT CAREFULLY.
