LM5009EVAL National Semiconductor, LM5009EVAL Datasheet - Page 2

• 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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Board Connection/Start-up
The input connections are made to the J1 connector. The load
is normally connected to the V1 and GND terminals of the J3
connector. Ensure the wires are adequately sized for the in-
tended load current. Before start-up a voltmeter should be
connected to the input terminals, and to the output terminals.
The load current should be monitored with an ammeter or a
current probe. It is recommended that the input voltage be
increased gradually to 12V, at which time the output voltage
should be 10V. If the output voltage is correct with 12V at
V
with evaluating the circuit.
Output Ripple Control
The LM5009 requires a minimum of 25 mVp-p ripple at the
FB pin, in phase with the switching waveform at the SW pin,
for proper operation. In the simplest configuration that ripple
is derived from the ripple at V
ripple current flowing through R4. That ripple voltage is at-
tenuated by the feedback resistors, requiring that the ripple
amplitude at V
by the gain factor. Options for reducing the output ripple are
discussed below, and the results are shown in the graph of
Figure 8.
A) Minimum Output Ripple: This evaluation board is sup-
plied configured for minimum ripple at V
zero ohms, and including components R6, C7 and C8. The
output ripple, which ranges from 5 mVp-p at V
mVp-p at V
output capacitor (C2), and the inductor’s ripple current, which
ranges from 32 mAp-p to 170 mAp-p over the input voltage
range. This performance applies only to continuous conduc-
tion mode as the ripple amplitude is higher in discontinuous
conduction mode. The ripple voltage required by the FB pin
IN
, then increase the input voltage as desired and proceed
IN
= 95V, is determined primarily by the ESR of
OUT1
be higher than the minimum of 25 mVp-p
OUT1
, generated by the inductor’s
OUT1
FIGURE 2. Minimum Ripple Using R6, C7, C8
by setting R4 to
IN
= 12V to 14
2
is generated by R6, C7 and C8 since the SW pin switches
from -1V to V
The values for R6 and C7 are chosen to generate a 30-40
mVp-p triangle waveform at their junction. That triangle wave
is then coupled to the FB pin through C8. The following pro-
cedure is used to calculate values for R6, C7 and C8:
1) Calculate the voltage V
where V
during the off-time (typically 1V), and V
voltage. For this circuit V
voltage at the R6/C7 junction, and is used in the next equa-
tion.
2) Calculate the R6 x C7 product:
where t
imum input voltage, and ΔV is the desired ripple amplitude at
the R6/C7 junction, 30 mVp-p for this example.
R6 and C7 are then chosen from standard value components
to satisfy the above product. For example, C7 can be 2200
pF requiring R6 to be 116 kΩ. A standard value 115 kΩ is
used in this board. C8 is chosen to be 0.01 µF, large com-
pared to C7. This portion of the circuit, as supplied on this
EVB, is shown in Figure 2.
ON
SW
is the maximum on-time (
is the absolute value of the voltage at the SW pin
V
IN
A
, and the right end of C7 is a virtual ground.
= V
OUT
- (V
20181106
A
A
calculates to 9.83V. This is the DC
:
SW
x (1 - (V
≊
3540 ns), V
IN
OUT
is the minimum input
/V
IN
)))
IN
is the min-