LM34910EVAL National Semiconductor, LM34910EVAL Datasheet - Page 10

• Manufacturer Part Number: LM34910EVAL
• Description: BOARD EVALUATION LM34910
• Manufacturer: National Semiconductor

Specifications of LM34910EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 5V
• Current - Output: 1A
• Voltage - Input: 8 ~ 36V
• Regulator Topology: Buck
• Frequency - Switching: 850kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM34910
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

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Applications Information
C4: The recommended value for C4 is 0.022 µF. A high
quality ceramic capacitor with low ESR is recommended as
C4 supplies a surge current to charge the buck switch gate
at turn-on. A low ESR also helps ensure a complete recharge
during each off-time.
C6: The capacitor at the SS pin determines the softstart
time, i.e. the time for the reference voltage at the regulation
comparator, and the output voltage, to reach their final value.
The time is determined from the following:
PC BOARD LAYOUT
The LM34910 regulation, over-voltage, and current limit
comparators are very fast, and respond to short duration
noise pulses. Layout considerations are therefore critical for
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optimum performance. The layout must be as neat and
compact as possible, and all of the components must be as
close as possible to their associated pins. The current loop
formed by D1, L1, C2 and the S
as small as possible. The ground connection from C2 to C1
should be as short and direct as possible.
If it is expected that the internal dissipation of the LM34910
will produce excessive junction temperatures during normal
operation, good use of the PC board’s ground plane can help
considerably to dissipate heat. The exposed pad on the
bottom of the IC package can be soldered to a ground plane,
and that plane should extend out from beneath the IC, and
be connected to ground plane on the board’s other side with
several vias, to help dissipate the heat. The exposed pad is
internally connected to the IC substrate. Additionally the use
of wide PC board traces, where possible, can help conduct
heat away from the IC. Judicious positioning of the PC board
within the end product, along with the use of any available air
flow (forced or natural convection) can help reduce the junc-
tion temperatures.
GND
and I
SEN
pins should be