Datasheet
LM5015
SNVS538C –NOVEMBER 2007–REVISED APRIL 2013
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Multiple resistors in series or parallel combinations for either R
O1
, or R
O2
, or both, may be necessary to set a
required output voltage. Note that the accuracy of the output voltage setting is determined by the tolerance of the
divider resistors as well as the accuracy of V
REF
. The accuracy of the LM5015 internal V
REF
is 1.5%, and the
most popular chip resistors have a tolerance of 1%, therefore the achievable output accuracy with the internal
error amplifier and 1% resistors is about 2.5%. To achieve better output voltage accuracy, use an external
voltage reference with higher precision and resistors of tighter tolerance, such as the 0.1%, resistors for R
O1
and
R
O2
.
PRINTED CIRCUIT BOARD LAYOUT
The LM5015 Current Sense and PWM comparators are very fast and may respond to short duration noise
pulses. The components at the HO, LO, COMP, EN, VCC and the RT pins should be as physically close as
possible to the IC, thereby minimizing noise pickup on the PC board tracks. The HO and LO output pins of the
LM5015 should have short, wide conductors to the power path inductors, transformers and capacitors in order to
minimize parasitic inductance that reduces efficiency and increases conducted and radiated noise. Ceramic
decoupling capacitors are recommended between the VIN pin to the AGND pin, between the PVIN pin and
PGND pin, and between the VCC pin to the AGND pin. Use short, direct connections to avoid clock jitter due to
ground voltage differentials. Small package surface mount X7R or X5R capacitors are preferred for high
frequency performance and limited variation over temperature and applied voltage.
If an application using the LM5015 produces high junction temperatures during normal operation, multiple vias
from the exposed metal pad on the underside of the IC package to a PC board ground plane will help conduct
heat away from the IC. Judicious positioning of the PC board within the end product, along with use of any
available air flow will help reduce the junction temperature. If using forced air cooling, avoid placing the LM5015
in the airflow shadow of large components, such as input or output capacitors, inductors or transformers.
Application Examples
The following schematics present four examples dc-dc converters utilizing the LM5015 switching regulator IC:
1. Non-Isolated Two-Switch Forward for 48V input and 5V 2.5A output,
2. Isolated Two-Switch Forward for 48V input and 5V 2.5A output
3. Isolated Two-Switch Flyback converter for 48V input and 5V 2.5A output,
4. A 1:1 dc-dc transformer with the input/output operating range of 5V to 15V
48V NON-ISOLATED TWO-SWITCH FORWARD
The Non-Isolated Two-Switch Forward converter shown in Figure 24 utilizes the internal voltage reference for the
regulation set-point. The output is +5V at 2.5A while the input voltage can vary from 36V to 72V. The switching
frequency is 300 kHz. An auxiliary winding on transformer (T1) provides 10V to power the LM5015 when the
output is in regulation. This disables the internal high voltage VCC LDO regulator and improves efficiency. The
converter can be shut down by driving the EN input below 1.26V with an open-collector or open-drain transistor.
An external synchronizing frequency can be applied to the SYNC input.
Figure 24. Non-Isolated Two-Switch Forward
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