LM5009EVAL/NOPB National Semiconductor, LM5009EVAL/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM5009EVAL/NOPB
• Description: EVAL BOARD FOR LM5009
• Manufacturer: National Semiconductor

Specifications of LM5009EVAL/NOPB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

cient voltage across the buck switch driver during each on-
time.
C5: This capacitor helps avoid supply voltage transients and
ringing due to long lead inductance at VIN. A low ESR, 0.1µF
ceramic chip capacitor is recommended, located close to the
LM5009.
FINAL CIRCUIT
The final circuit is shown in
and the resulting performance is shown in
Figure
50mA to 200mA.
MINIMUM LOAD CURRENT
A minimum load current of 1 mA is required to maintain proper
operation. If the load current falls below that level, the boot-
strap capacitor may discharge during the long off-time, and
the circuit will either shutdown, or cycle on and off at a low
frequency. If the load current is expected to drop below 1 mA
in the application, the feedback resistors should be chosen
low enough in value so they provide the minimum required
current at nominal Vout.
PC BOARD LAYOUT
The LM5009 regulation and over-voltage comparators are
very fast, and as such will respond to short duration noise
9. For these graphs, the load current was varied from
Figure
5. The circuit was tested,
Figure 6
FIGURE 5. LM5009 Example Circuit
through
11
pulses. Layout considerations are therefore critical for opti-
mum performance. The components at pins 1, 2, 3, 5, and 6
should be as physically close as possible to the IC, thereby
minimizing noise pickup in the PC tracks. The current loop
formed by D1, L1, and C2 should be as small as possible. The
ground connection from C2 to C1 should be as short and di-
rect as possible.
If the internal dissipation of the LM5009 produces excessive
junction temperatures during normal operation, good use of
the pc board’s ground plane can help considerably to dissi-
pate heat. The exposed pad on the bottom of the LLP-8
package can be soldered to a ground plane on the PC board,
and that plane should extend out from beneath the IC to help
dissipate the heat. Additionally, the use of wide PC board
traces, where possible, can also 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 (forced or
natural convection) can help reduce the junction tempera-
tures.
20165822
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