LTM8047 LINER [Linear Technology], LTM8047 Datasheet - Page 13

• Manufacturer Part Number: LTM8047
• Description: 3.1VIN to 32VIN Isolated ?Module DC/DC Converter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Isolation and Working Voltage
The LTM8048 isolation is tested by tying all of the primary
pins together, all of the secondary pins together and
subjecting the two resultant circuits to a differential of
±725VDC for one second. This establishes the isolation
voltage rating, but it does not determine the working volt-
age rating, which is subject to the application board layout
and possibly other factors. The metal to metal separation
of the primary and secondary throughout the LTM8048
substrate is 0.44mm.
V
V
300mA regulator. At full load, its dropout is less than
430mV over temperature. Its output is set by applying a
resistor from the R
can be calculated by the equation:
V
The LTM8048 cannot tolerate a reverse voltage from V
to V
during operation, the LTM8048 may be damaged. To protect
against this condition, a low forward drop power Schottky
diode has been integrated into the LTM8048, anti-parallel
to V
reverse voltage faults. Reverse voltage faults can be both
steady state and transient. An example of a steady state
voltage reversal is accidentally misconnecting a powered
LTM8048 to a negative voltage source. An example of
transient voltage reversals is a momentary connection to
a negative voltage. It is also possible to achieve a V
reversal if the load is short-circuited through a long cable.
The inductance of the long cable forms an LC tank circuit
with the V
Avoid these conditions.
OUT2
OUT2
OUT1
R
OUT1
OUT
ADJ2
Post Regulator
to V
is produced by a high performance low dropout
–
/V
during operation. If V
=
OUT1
OUT
OUT
V
OUT2
–
–
608.78
. This can protect the output against many
capacitance, which drive V
Reverse Voltage
– 1.22
ADJ2
pin to GND; the value of R
kΩ
OUT
–
raises above V
OUT1
negative.
OUT1
OUT1
OUT1
ADJ2
V
Noise Performance
The V
of a 0.01μF bypass capacitor from V
to lower output voltage noise. A good quality low leakage
capacitor, such as a X5R or X75 ceramic, is recommended.
This capacitor will bypass the reference of the regulator,
lowering the output voltage noise to as low as 20μV
Using a bypass capacitor has the added benefit of improv-
ing transient response.
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8048. The LTM8048 is neverthe-
less a switching power supply, and care must be taken to
minimize electrical noise to ensure proper operation. Even
with the high level of integration, you may fail to achieve
specified operation with a haphazard or poor layout. See
Figure 1 for a suggested layout. Ensure that the grounding
and heat sinking are acceptable.
OUT2
V
C
C
V
Figure 1. Layout Showing Suggested External Components,
Planes and Thermal Vias
OUT1
OUT1
OUT2
OUT2
V
OUT2
OUT
Post Regulator Bypass Capacitance and Low
–
linear regulator may be used with the addition
THERMAL/INTERCONNECT VIAS
ADJ2
BYP
LTM8048
GND
OUT
C
LTM8048
IN
to the BYP pin
RUN
ADJ1
13
BIAS
V
RMS
IN
SS
8048fa
8048 F01
.