LM3488MM National Semiconductor, LM3488MM Datasheet - Page 19

• Manufacturer Part Number: LM3488MM
• Description: IC, N-CH CONTROLLER, MSOP-8
• Manufacturer: National Semiconductor

Specifications of LM3488MM

• Primary Input Voltage: 40V
• No. Of Outputs: 1
• Output Current: 1A
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +125°C
• Termination Type: SMD
• Input Voltage Primary Min: 2.95V
• Output Voltage Min: 1.26V
• Rohs Compliant: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

In the above equation, V
FET, Q, and V
POWER MOSFET SELECTION
As in boost converter, the parameters governing the selection
of the MOSFET are the minimum threshold voltage, V
(MIN)
reverse transfer capacitance, C
to source voltage, V
SEPIC is given by:
The selected MOSFET should satisfy the condition:
The peak switch current is given by:
The rms current through the switch is given by:
POWER DIODE SELECTION
The Power diode must be selected to handle the peak current
and the peak reverse voltage. In a SEPIC, the diode peak
current is the same as the switch peak current. The off-state
voltage or peak reverse voltage of the diode is V
Similar to the boost converter, the average diode current is
equal to the output current. Schottky diodes are recommend-
ed.
SELECTION OF INDUCTORS L1 AND L2
Proper selection of the inductors L1 and L2 to maintain con-
stant current mode requires calculations of the following pa-
rameters.
Average current in the inductors:
, the on-resistance, R
V
DIODE
SW(PEAK)
V
is the forward voltage drop of the diode.
DS(MAX)
DS(MAX)
Q
= V
DS(ON)
is the on-state voltage of the MOS-
IN
. The peak switch voltage in a
> V
+ V
, the total gate charge, Q
RSS
SW(PEAK)
OUT
, and the maximum drain
+ V
DIODE
FIGURE 14. Typical SEPIC Converter
IN
+ V
g
, the
OUT
TH
.
19
Peak to peak ripple current, to calculate core loss if neces-
sary:
maintains the condition I
mode.
Peak current in the inductor, to ensure the inductor does not
saturate:
I
L2AVE
L
> Δi
= I
L
/2 to ensure constant current
OUT
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