LM3488MM National Semiconductor, LM3488MM Datasheet - Page 16

• 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

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will operate in discontinuous conduction mode. If Δi
er than I
converter will operate in continuous conduction mode. All the
analysis in this datasheet assumes operation in continuous
conduction mode. To operate in continuous conduction
mode, the following conditions must be met:
Choose the minimum I
common choice is to set Δi
propriate core size for the inductor involves calculating the
average and peak currents expected through the inductor. In
a boost converter,
and I
where
L_peak
L
, the inductor current will stay above zero and the
= I
L
(max) + Δi
OUT
L
(max),
I
L
L
to determine the minimum L. A
> Δi
to 30% of I
L
L
. Choosing an ap-
FIGURE 12. Adjusting the Output Voltage
L
is small-
16
A core size with ratings higher than these values should be
chosen. If the core is not properly rated, saturation will dra-
matically reduce overall efficiency.
The LM3488 can be set to switch at very high frequencies.
When the switching frequency is high, the converter can be
operated with very small inductor values. With a small induc-
tor value, the peak inductor current can be extremely higher
than the output currents, especially under light load condi-
tions.
The LM3488 senses the peak current through the switch. The
peak current through the switch is the same as the peak cur-
rent calculated above.
PROGRAMMING THE OUTPUT VOLTAGE
The output voltage can be programmed using a resistor di-
vider between the output and the feedback pins, as shown in
Figure
the feedback pin is 1.26V. R
the equation,
A 100pF capacitor may be connected between the feedback
and ground pins to reduce noise.
12. The resistors are selected such that the voltage at
F1
and R
10138820
F2
can be selected using