LM5002MA/NOPB National Semiconductor, LM5002MA/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM5002MA/NOPB
• Description: IC REG SWITCH MODE HV 8-SOIC
• Manufacturer: National Semiconductor
• Type: Step-Up (Boost), Flyback, Forward Converter, Sepicr

Specifications of LM5002MA/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 500mA
• Frequency - Switching: 1.5MHz
• Voltage - Input: 3.1 ~ 75 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Power - Output: -
• Other names: LM5002MA

www.national.com
Printed Circuit Board Layout
The LM5002 Current Sense and PWM comparators are very
fast and may respond to short duration noise pulses. The
components at the SW, COMP, EN and the RT pins should
be as physically close as possible to the IC, thereby minimiz-
ing noise pickup on the PC board tracks.
The SW output pin of the LM5002 should have a short, wide
conductor to the power path inductors, transformers and ca-
pacitors in order to minimize parasitic inductance that reduces
efficiency and increases conducted and radiated noise. Ce-
ramic decoupling capacitors are recommended between the
VIN pin to the GND pin and between the VCC pin to the GND
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 per-
formance and limited variation over temperature and applied
voltage.
If an application using the LM5002 produces high junction
temperatures during normal operation, multiple vias from the
GND pin 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 temperatures. If using forced air
cooling, avoid placing the LM5002 in the airflow shadow of
large components, such as input capacitors, inductors or
transformers.
Application Circuit Examples
The following schematics present examples of a Non-Isolated
Flyback, Isolated Flyback, Boost, 24V SEPIC and a 12V Au-
tomotive range SEPIC converters utilizing the LM5002
switching regulator.
NON-ISOLATED FLYBACK
The Non-Isolated Flyback converter (Figure 6) utilizes the in-
ternal voltage reference for the regulation setpoint. The output
is +5V at 500mA while the input voltage can vary from 16V to
42V. The switching frequency is set to 250kHz. An auxiliary
winding on transformer (T1) provides 7.5V to power the
LM5002 when the output is in regulation. This disables the
internal high voltage VCC LDO regulator and improves effi-
ciency. The input under-voltage threshold is 13.9V. The con-
verter 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.
An optional soft-start circuit is connected to the COMP pin
input. When power is applied, the soft-start capacitor (C7) is
discharged and limits the voltage applied to the PWM com-
parator by the internal error amplifier. The internal ~5 kΩ
COMP pull-up resistor charges the soft-start capacitor until
regulation is achieved. The VCC pull-up resistor (R7) contin-
ues to charge C7 so that the soft-start circuit will not affect the
compensation network in normal operation. If the output ca-
14
pacitance is small, the soft-start circuit can be adjusted to limit
the power-on output voltage overshoot. If the output capaci-
tance is sufficiently large, no soft-start circuit is needed be-
cause the LM5002 will gradually charge the output capacitor
by current limiting at approximately 500mA (I
tion is achieved.
ISOLATED FLYBACK
The Isolated Flyback converter (Figure 7) utilizes a 2.5V volt-
age reference (LM431) located on the isolated secondary
side for the regulation setpoint. The LM5002 internal error
amplifier is disabled by grounding the FB pin. The LM431
controls the current through the opto-coupler LED, which sets
the COMP pin voltage. The R4 and C3 network boosts the
phase response of the opto-coupler to increase the loop
bandwidth. The output is +5V at 500mA and the input voltage
ranges from 16V to 42V. The switching frequency is set to
250kHz.
BOOST
The Boost converter (Figure 8) utilizes the internal voltage
reference for the regulation setpoint. The output is +48V at
125 mA, while the input voltage can vary from 16V to 36V.
The switching frequency is set to 250kHz. The internal VCC
regulator provides 6.9V bias power, since there isn’t a simple
method for creating an auxiliary voltage with the boost topol-
ogy. Note that the boost topology does not provide output
short-circuit protection because the power MOSFET cannot
interrupt the path between the input and the output.
24V SEPIC
The 24V SEPIC converter (Figure 9) utilizes the internal volt-
age reference for the regulation setpoint. The output is +24V
at 125 mA while the input voltage can vary from 16V to 48V.
The switching frequency is set to 250kHz. The internal VCC
regulator provides 6.9V bias power for the LM5002. An aux-
iliary voltage can be created by adding a winding on L2 and
a diode into the VCC pin.
12V AUTOMOTIVE SEPIC
The 12V Automotive SEPIC converter (Figure 10) utilizes the
internal bandgap voltage reference for the regulation setpoint.
The output is +12V at 25 mA while the input voltage can vary
from 3.1V to 60V. The output current rating can be increased
if the minimum VIN voltage requirement is increased. The
switching frequency is set to 750kHz. The internal VCC reg-
ulator provides 6.9V bias power for the LM5002. The output
voltage can be used as an auxiliary voltage if the nominal VIN
voltage is greater than 12V by adding a diode from the output
into the VCC pin. In this configuration, the minimum input
voltage must be greater than 12V to prevent the internal VCC
to VIN diode from conducting. If the applied VCC voltage ex-
ceeds the minimum VIN voltage, then an external blocking
diode is required between the VIN pin and the power source
to block current flow from VCC to the input supply.
LIM
) until regula-