LM22677EVAL/NOPB National Semiconductor, LM22677EVAL/NOPB Datasheet - Page 2

• Manufacturer Part Number: LM22677EVAL/NOPB
• Description: BOARD EVALUATION FOR LM22677
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r

Specifications of LM22677EVAL/NOPB

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 5A
• Voltage - Input: 4.5 ~ 42V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM22677
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -
• Other names: *LM22677EVAL; LM22677EVAL

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Evaluation Board Setup
Before applying power to the LM22677 evaluation board, all
external connections should be verified. The external power
supply must be turned off and connected with proper polarity
to the VIN and GND posts. A load resistor or electronic load
should be connected between the VOUT and GND posts as
desired. Both the VIN and VOUT connections should use the
closest GND posts respective to VIN or VOUT. The output
voltage can be monitored with a multi-meter or oscilloscope
at the VOUT post.
Once all connections to the evaluation board have been ver-
ified, input power can be applied. A load resistor or electronic
load does not require connection during startup. If the EN test
point is left floating, the output voltage will ramp up when an
input voltage is applied. Make sure that the external power
supply (input voltage power source) is capable of providing
enough current so that the adjusted output voltage can be
obtained. Keep in mind that the startup current will be greater
than the steady state current.
Synchronization and Adjustable
Frequency
A SYNC test point is provided to allow synchronization of the
LM22677 to an external clock signal. Space for a frequency
adjust resistor, R3, is also provided. Refer to the LM22677
datasheet for more details about the synchronizing and ad-
justable frequency features.
Precision Enable
The EN test point provided on the LM22677 evaluation board
can be used to shut down the LM22677 when connecting this
test point to ground.
C1, C7
Ref #
C2
C3
C4
C5
D1
R1
R2
R3
U1
L1
TABLE 1. LM22677EVAL Bill of Materials for VOUT = 3.3V, Designed for 5A output current
180 µF 6.3V 12 mΩ Polymer Aluminum
4.7 µH 8.5A WE-PD XL
22 µF 63V electrolytic
6.8 µF 50V ceramic
60V 5A CMSH5-60
10 nF 50V ceramic
Not populated
Not populated
1.54 kΩ 1%
976Ω 1%
Value
2
National Semiconductor
Central Semiconductor
Component Selection
Before changing the default components refer to the
LM22677 datasheet for information regarding component se-
lection. The WEBENCH
tool is also available at www.national.com.
The output voltage is adjustable with resistors R1 and R2
shown in the schematic. Any changes to these evaluation
board feedback resistors may require changes to the inductor
and output capacitor values. It is especially important to
change the output capacitor, C4, if the output voltages are
adjusted higher than 5V. The Schottky diode, D1, has a volt-
age rating of 60V to allow for a 42V maximum input voltage.
If the input voltage is below 38V, a 40V Schottky diode may
be used with a lower forward voltage to improve efficiency.
For improved heat dissipation, a Schottky diode in a D2PAK
package may be selected for higher efficiency. The input ca-
pacitor, C2, is not always required. This capacitor is placed
on the evaluation board to make the application robust and
minimize input voltage ringing if power is suddenly applied.
Capacitor C2 also helps stabilize the transfer function of the
converter loop. Input capacitors C1 and C7 provide the high
di/dt portion of the switch current. Both capacitors are select-
ed with appropriate values intended only for the evaluation of
the LM22677. For production designs, the impedance of the
power source as well as the ripple current rating of the se-
lected input capacitors need to be taken into consideration
and modified accordingly. See the LM22677 datasheet for
more information.
Output capacitor C5 is not populated but space is provided to
add a second output capacitor. This second output capacitor
may be used to further reduce output voltage ripple.
Panasonic
Panasonic
Supplier
Coilcraft
Wurth
TDK
TDK
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designer online circuit simulation
CRCW0603976RFKEA
CRCW06031K54FKEA
C4532X7R1H685M
C1608X7R1H103K
MSS1278-472MLD
LM22677TJ-ADJ
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Part Number
CMSH5-60
74477004