LM2830XMF/NOPB National Semiconductor, LM2830XMF/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM2830XMF/NOPB
• Description: IC REGULATOR BUCK 1A SOT23-5
• Manufacturer: National Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM2830XMF/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 4.5 V
• Current - Output: 1A
• Frequency - Switching: 1.6MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM2830XMF; LM2830XMFTR

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both input and output capacitors and have very low ESL. For
MLCCs it is recommended to use X7R or X5R type capacitors
due to their tolerance and temperature characteristics. Con-
sult capacitor manufacturer datasheets to see how rated
capacitance varies over operating conditions.
OUTPUT CAPACITOR
The output capacitor is selected based upon the desired out-
put ripple and transient response. The initial current of a load
transient is provided mainly by the output capacitor. The out-
put ripple of the converter is:
When using MLCCs, the ESR is typically so low that the ca-
pacitive ripple may dominate. When this occurs, the output
ripple will be approximately sinusoidal and 90° phase shifted
from the switching action. Given the availability and quality of
MLCCs and the expected output voltage of designs using the
LM2830, there is really no need to review any other capacitor
technologies. Another benefit of ceramic capacitors is their
ability to bypass high frequency noise. A certain amount of
switching edge noise will couple through parasitic capaci-
tances in the inductor to the output. A ceramic capacitor will
bypass this noise while a tantalum will not. Since the output
capacitor is one of the two external components that control
the stability of the regulator control loop, most applications will
require a minimum of 22 µF of output capacitance. Capaci-
tance often, but not always, can be increased significantly
with little detriment to the regulator stability. Like the input ca-
pacitor, recommended multilayer ceramic capacitors are X7R
or X5R types.
CATCH DIODE
The catch diode (D1) conducts during the switch off-time. A
Schottky diode is recommended for its fast switching times
and low forward voltage drop. The catch diode should be
chosen so that its current rating is greater than:
The reverse breakdown rating of the diode must be at least
the maximum input voltage plus appropriate margin. To im-
prove efficiency, choose a Schottky diode with a low forward
voltage drop.
I
D1
= I
OUT
x (1-D)
12
OUTPUT VOLTAGE
The output voltage is set using the following equation where
R2 is connected between the FB pin and GND, and R1 is
connected between V
is 10kΩ. When designing a unity gain converter (Vo = 0.6V),
R1 should be between 0Ω and 100Ω, and R2 should be equal
or greater than 10kΩ.
PCB LAYOUT CONSIDERATIONS
When planning layout there are a few things to consider when
trying to achieve a clean, regulated output. The most impor-
tant consideration is the close coupling of the GND connec-
tions of the input capacitor and the catch diode D1. These
ground ends should be close to one another and be connect-
ed to the GND plane with at least two through-holes. Place
these components as close to the IC as possible. Next in im-
portance is the location of the GND connection of the output
capacitor, which should be near the GND connections of CIN
and D1. There should be a continuous ground plane on the
bottom layer of a two-layer board except under the switching
node island. The FB pin is a high impedance node and care
should be taken to make the FB trace short to avoid noise
pickup and inaccurate regulation. The feedback resistors
should be placed as close as possible to the IC, with the GND
of R1 placed as close as possible to the GND of the IC. The
V
any other traces that are switching. High AC currents flow
through the V
short and wide as possible. However, making the traces wide
increases radiated noise, so the designer must make this
trade-off. Radiated noise can be decreased by choosing a
shielded inductor. The remaining components should also be
placed as close as possible to the IC. Please see Application
Note AN-1229 for further considerations and the LM2830 de-
mo board as an example of a four-layer layout.
OUT
trace to R2 should be routed away from the inductor and
IN
, SW and V
O
V
and the FB pin. A good value for R2
REF
OUT
= 0.60V
traces, so they should be as