LM5008AEVAL/NOPB National Semiconductor, LM5008AEVAL/NOPB Datasheet - Page 2

• Manufacturer Part Number: LM5008AEVAL/NOPB
• Description: BOARD EVAL LM5008
• Manufacturer: National Semiconductor

Specifications of LM5008AEVAL/NOPB

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 5V
• Current - Output: 300mA
• Voltage - Input: 8 ~ 75 V
• Regulator Topology: Buck
• Frequency - Switching: 130kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5008A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

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Board Layout and Probing
The pictorial in
components. The following should be kept in mind when the
board is powered:
1) When operating at high input voltage and high load current,
forced air flow may be necessary.
2) The LM5008A, and diode D1 may be hot to the touch when
operating at high input voltage and high load current.
3) Use CAUTION when probing the circuit at high input volt-
ages to prevent injury, as well as possible damage to the
circuit.
4) At maximum load current, the wire size and length used to
connect the load becomes important. Ensure there is not a
significant drop in the wires between this evaluation board
and the load.
Board Connection/Start-up
The input connections are made to the J1 connector. The load
is connected to the J2 (OUT) and J3 (GND) terminals. Ensure
the wires are adequately sized for the intended 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 rec-
Figure 1
shows the placement of the circuit
FIGURE 2. Lowest Cost Configuration
2
ommended that the input voltage be increased gradually to
8V, at which time the output voltage should be 5V. If the output
voltage is correct with 8V at VIN, then increase the input volt-
age as desired and proceed with evaluating the circuit. DO
NOT EXCEED 75V AT VIN.
Output Ripple Control
The LM5008A 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. The required ripple can be supplied from
ripple at V
Option A below. Options B and C provide lower output ripple
with one or two additional components.
Option A) Lowest Cost Configuration: In this configuration
R5 is installed in series with the output capacitance (C2).
Since
chosen to generate
minimum ripple current in this circuit is
mum V
≊
application can accept this ripple level, this is the most eco-
nomical solution. The circuit is shown in
8.
54 mVp-p to
≥
IN
25 mVp-p are required at the FB pin, R5 must be
. Using 0.82Ω for R5, the ripple at V
OUT
, through the feedback resistors as described in
≊
135 mVp-p over the input voltage range. If the
≥
50 mVp-p at V
OUT
Figure
≊
, knowing that the
66 mAp-p at mini-
OUT
2. See
30086303
ranges from
Figure