LM5009EVAL National Semiconductor, LM5009EVAL Datasheet - Page 4

• Manufacturer Part Number: LM5009EVAL
• Description: BOARD EVALUATION LM5009
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5009EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 10V
• Current - Output: 150mA
• Voltage - Input: 12 ~ 95V
• Regulator Topology: Buck
• Frequency - Switching: 240Hz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5009
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -
• Lead Free Status / Rohs Status: Not Compliant

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Current Limit
The LM5009 contains an intelligent current limit off-timer. The
current limit threshold is 310 mA, ±60 mA. If the current in the
buck switch (the peak of the inductor’s current waveform)
reaches the threshold the present on-time cycle is immedi-
ately terminated, and a non-resetable off-time is initiated. The
length of the off-time is controlled by an external resistor (R5)
and the voltage at the FB pin. If FB = 0V (output is shorted to
ground) the off-time is the preset maximum of 35 µs. This off-
time ensures safe short circuit operation to the maximum
input voltage of 95V. In cases of less severe overload where
the output voltage, and the voltage at FB, is above ground the
current limit off-time is less than 35 µs. The shorter off-times
reduces the amount of foldback, recovery time, and also re-
duces the startup time. The current limit off-time is calculated
from the following equation:
FIGURE 5. Complete Evaluation Board Schematic
4
The current limit off-time ranges from 5.5 µs to 35 µs as V
varies from 2.5V to 0V, with R5 = 255 kΩ. The guideline for
selecting R5’s value is that the current limit off-time (at V
2.5V) should be slightly longer than the maximum off-time
encountered in normal operation. Setting a shorter off-time
could result in inadequate overload protection, and setting a
much longer off-time can affect the startup operation.
Minimum Load Current
The LM5009 requires a minimum load current of
ensure the boost capacitor (C5) is recharged sufficiently dur-
ing each off-time. In this evaluation board, the minimum load
current is provided by the feedback resistors (R2, R3), allow-
ing the board’s minimum load current to be specified at zero.
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20181111
500 µA to
FB
FB
=