LM34910EVAL National Semiconductor, LM34910EVAL Datasheet
LM34910EVAL
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
-
© 2004 National Semiconductor Corporation
LM34910 Evaluation Board
Introduction
The LM34910EVAL evaluation board provides the design
engineer with a fully functional buck regulator, employing the
constant on-time (COT) operating principle. This evaluation
board provides a 5V output from an input range of 8V - 36V.
The circuit provides load currents
set at )1.3A
The board’s specification are:
Theory of Operation
Refer to the board’s schematic in Figure 2, which contains a
simplified block diagram of the LM34910. When the circuit is
in regulation, the buck switch is on each cycle for a time
determined by R1 and V
board will range from )775 ns at V
= 36V. At the end of the on-time, the feedback voltage at FB
is above 2.5V, and the Minimum Off-Timer ensures the buck
switch is off for at least 280 ns. In normal operation, the
off-time is longer. During the off-time, the output capacitor
(C6) discharges, and when the output voltage falls so that
the voltage at FB is below 2.5V, the comparator output
switches to initiate a new on-time. As required by the
datasheet, this circuit provides a minimum of 25 mVp-p
ripple at the FB pin. Refer to the LM34910 data sheet for a
more detailed block diagram, and a complete description of
the various functional blocks.
Board Layout and Probing
The pictorial in Figure 1 shows the placement of the circuit
components. The following should be kept in mind when the
board is powered:
IN
. The on-time in this evaluation
>
IN
1A, with the current limit
= 8V, to )200 ns at V
AN201313
FIGURE 1. Evaluation Board - Top Side
IN
National Semiconductor
Application Note 1349
Dennis Morgan
November 2004
• Input Voltage: 8V to 36V
•
• Maximum Continuous Output current: 1.0A
• Current Limit: 1.3A
• Measured Efficiency: 92% (V
• Switching Frequency: )850 kHz
• Size: 0.75 in. x 1.5 in. x 0.47 in
1) When operating at high input voltage and high load cur-
rent, forced air flow IS NECESSARY.
2) The LM34910, and the diode D1 will be hot to the touch
when operating at high input voltage and high load current.
3) Use CAUTION when probing the circuit due to the com-
pact layout.
4) At maximum load current (1A), the wire size and length
used to connect the load becomes important. Ensure there is
not a significant drop in the wires.
Board Connection/Start-up
The input connections are made to the J1 connector. The
load is normally connected to the OUT1 and GND terminals
of the J3 connector. 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 recommended that the input
voltage be increased gradually to 8V, at which time the
output voltage will be 5V. If that indicates correctly, then
proceed with evaluating the circuit.
Output Voltage: 5V,
±
3%
IN
= 8V, I
OUT
20131301
= 400 mA)
www.national.com
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LM34910EVAL Summary of contents
Page 1
... LM34910 Evaluation Board Introduction The LM34910EVAL evaluation board provides the design engineer with a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 5V output from an input range 36V. > The circuit provides load currents 1A, with the current limit set at )1.3A The board’ ...
Page 2
Low Ripple Output The ripple voltage at OUT1 will range from )60 mVp-p (at = 8V) to )160 mVp-p ( 36V low ripple output desired, connect the load to OUT2. The ripple ...
Page 3
FIGURE 3. Efficiency vs Load Current 20131304 FIGURE 4. Efficiency 20131303 www.national.com ...
Page 4
PCB Layout www.national.com Board Silkscreen Board Top Layer Board Bottom Layer 4 20131305 20131306 20131307 ...
Page 5
... BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. ...