LM2830XQMFX/NOPB [NSC]
IC 1.75 A SWITCHING REGULATOR, 1950 kHz SWITCHING FREQ-MAX, PDSO5, SOT-23, 5 PIN, Switching Regulator or Controller;
| 型号： | LM2830XQMFX/NOPB |
| 厂家： | 
National Semiconductor |
| 描述： | IC 1.75 A SWITCHING REGULATOR, 1950 kHz SWITCHING FREQ-MAX, PDSO5, SOT-23, 5 PIN, Switching Regulator or Controller 信息通信管理 开关 光电二极管 |
| 文件： | 总24页 (文件大小：377K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 1, 2008
LM2830
High Frequency 1.0A Load - Step-Down DC-DC Regulator
General Description
Features
The LM2830 regulator is a monolithic, high frequency, PWM
step-down DC/DC converter in a 5 pin SOT23 and a 6 Pin
LLP package. It provides all the active functions to provide
local DC/DC conversion with fast transient response and ac-
curate regulation in the smallest possible PCB area. With a
minimum of external components, the LM2830 is easy to use.
The ability to drive 1.0A loads with an internal 130 mΩ PMOS
switch using state-of-the-art 0.5 µm BiCMOS technology re-
sults in the best power density available. The world-class
control circuitry allows on-times as low as 30ns, thus sup-
porting exceptionally high frequency conversion over the en-
tire 3V to 5.5V input operating range down to the minimum
output voltage of 0.6V. Switching frequency is internally set
to 1.6 MHz, or 3.0 MHz, allowing the use of extremely small
surface mount inductors and chip capacitors. Even though the
operating frequency is high, efficiencies up to 93% are easy
to achieve. External shutdown is included, featuring an ultra-
low stand-by current of 30 nA. The LM2830 utilizes current-
mode control and internal compensation to provide high-
performance regulation over a wide range of operating
conditions. Additional features include internal soft-start cir-
cuitry to reduce inrush current, pulse-by-pulse current limit,
thermal shutdown, and output over-voltage protection.
Space Saving SOT23-5 Package
■
■
■
■
Input voltage range of 3.0V to 5.5V
Output voltage range of 0.6V to 4.5V
1.0A output current
High Switching Frequencies
1.6MHz (LM2830X)
3.0MHz (LM2830Z)
■
130mΩ PMOS switch
0.6V, 2% Internal Voltage Reference
■
■
■
■
■
■
Internal soft-start
Current mode, PWM operation
Thermal Shutdown
Over voltage protection
Applications
Local 5V to Vcore Step-Down Converters
■
■
■
■
■
■
Core Power in HDDs
Set-Top Boxes
USB Powered Devices
DSL Modems
Automotive
Typical Application Circuit
20197464
© 2008 National Semiconductor Corporation
201974
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20197481
Connection Diagrams
5-Pin SOT-23 20197403
20197401
6-Pin LLP
Ordering Information
Frequency
Order Number
Package
Type
NSC Package
Drawing
Top Mark
Supplied As
Features
Option
LM2830XMF
1000 units T& R
3000 units T& R
1000 units T& R
3000 units T& R
250 units T& R
SKTB
LM2830XMFX
LM2830XQMF
AEC-Q100 Grade 1
qualified. Automotive
Grade Production
Flow*
1.6MHz
SOT23-5
MF05A
LM2830XQMFX
LM2830XQMFE
LM2830ZMF
SUFB
1000 units T& R
3000 units T& R
1000 units T& R
4500 units T& R
SOT23-5
LLP-6
MF05A
SKXB
L192B
LM2830ZMFX
3MHz
LM2830ZSD
SDE06A
LM2830ZSDX
*Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including defect detection methodologies.
Reliability qualification is compliant with the requirements and temperature grades defined in the AEC-Q100 standard. Automotive grade products are identified
with the letter Q. For more information go to http://www.national.com/automotive.
www.national.com
2
Pin Descriptions 5-Pin SOT23
Pin
1
Name
SW
Function
Output switch. Connect to the inductor and catch diode.
2
GND
Signal and power ground pin. Place the bottom resistor of the feedback network as close as
possible to this pin.
3
4
FB
EN
Feedback pin. Connect to external resistor divider to set output voltage.
Enable control input. Logic high enables operation. Do not allow this pin to float or be greater
than VIN + 0.3V.
5
VIN
Input supply voltage.
Pin Descriptions 6-Pin LLP
Pin
1
Name
FB
Function
Feedback pin. Connect to external resistor divider to set output voltage.
2
GND
Signal and power ground pin. Place the bottom resistor of the feedback network as close
as possible to this pin.
3
4
5
6
SW
VIND
VINA
EN
Output switch. Connect to the inductor and catch diode.
Power Input supply.
Control circuitry supply voltage. Connect VINA to VIND on PC board.
Enable control input. Logic high enables operation. Do not allow this pin to float or be greater
than VINA + 0.3V.
DAP
Die Attach Pad
Connect to system ground for low thermal impedance, but it cannot be used as a primary
GND connection.
3
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Junction Temperature (Note 2)
Storage Temperature
Soldering Information
150°C
−65°C to +150°C
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ꢀInfrared or Convection Reflow
(15 sec)
220°C
VIN
-0.5V to 7V
-0.5V to 3V
-0.5V to 7V
-0.5V to 7V
2kV
FB Voltage
EN Voltage
SW Voltage
ESD Susceptibility
Operating Ratings
VIN
3V to 5.5V
−40°C to +125°C
Junction Temperature
Electrical Characteristics VIN = 5V unless otherwise indicated under the Conditions column. Limits in standard
type are for TJ = 25°C only; limits in boldface type apply over the junction temperature (TJ) range of -40°C to +125°C. Minimum
and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely
parametric norm at TJ = 25°C, and are provided for reference purposes only.
Symbol
Parameter
Feedback Voltage
Conditions
Min
Typ
Max
Units
LLP-6 and SOT23-5
Package
0.588
0.600
0.612
VFB
V
Feedback Voltage Line Regulation
Feedback Input Bias Current
VIN = 3V to 5V
0.02
%/V
nA
V
ΔVFB/VIN
IB
0.1
2.73
2.3
0.43
1.6
3.0
94
100
VIN Rising
VIN Falling
2.90
Undervoltage Lockout
UVLO Hysteresis
UVLO
1.85
V
LM2830-X
1.2
2.25
86
1.95
3.75
FSW
DMAX
DMIN
Switching Frequency
MHz
LM2830-Z
LM2830-X
Maximum Duty Cycle
Minimum Duty Cycle
Switch On Resistance
%
%
LM2830-Z
82
90
LM2830-X
5
LM2830-Z
7
LLP-6 Package
SOT23-5 Package
VIN = 3.3V
150
130
1.75
RDS(ON)
ICL
mΩ
A
195
0.4
Switch Current Limit
Shutdown Threshold Voltage
Enable Threshold Voltage
Switch Leakage
1.2
1.8
VEN_TH
V
ISW
IEN
100
100
3.3
4.3
30
nA
nA
Enable Pin Current
Sink/Source
LM2830X VFB = 0.55
LM2830Z VFB = 0.55
All Options VEN = 0V
5
mA
mA
nA
Quiescent Current (switching)
Quiescent Current (shutdown)
IQ
6.5
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Symbol
Parameter
Junction to Ambient
0 LFPM Air Flow (Note 3)
Junction to Case (Note 3)
Thermal Shutdown Temperature
Conditions
LLP-6 Package
Min
Typ
80
Max
Units
θJA
°C/W
SOT23-5 Package
LLP-6 Package
118
18
θJC
°C/W
°C
SOT23-5 Package
80
TSD
165
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Range indicates conditions for which the device is
intended to be functional, but does not guarantee specfic performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device.
Note 3: Applies for packages soldered directly onto a 3” x 3” PC board with 2oz. copper on 4 layers in still air.
5
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Typical Performance Characteristics
All curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this
datasheet. TJ = 25°C, unless otherwise specified.
η vs Load "X" Vin = 5V, Vo = 1.8V & 3.3V
η vs Load "Z" Vin = 5V, Vo = 3.3V & 1.8V
20197439
20197442
Load Regulation
Vin = 3.3V, Vo = 1.8V (All Options)
η vs Load "X and Z" Vin = 3.3V, Vo = 1.8V
20197489
20197483
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Load Regulation
Vin = 5V, Vo = 1.8V (All Options)
Load Regulation
Vin = 5V, Vo = 3.3V (All Options)
20197484
20197485
Oscillator Frequency vs Temperature - "X"
Oscillator Frequency vs Temperature - "Z"
20197424
20197436
Current Limit vs Temperature
Vin = 3.3V
RDSON vs Temperature (LLP-6 Package)
20197487
20197486
7
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RDSON vs Temperature (SOT23-5 Package)
LM2830X IQ (Quiescent Current)
20197488
20197428
LM2830Z IQ (Quiescent Current)
Line Regulation
Vo = 1.8V, Io = 500mA
20197437
20197453
VFB vs Temperature
20197427
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8
Gain vs Frequency
(Vin = 5V, Vo = 1.2V @ 1A)
Phase Plot vs Frequency
(Vin = 5V, Vo = 1.2V @ 1A)
20197456
20197457
Simplified Block Diagram
20197404
FIGURE 1.
9
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Applications Information
THEORY OF OPERATION
SOFT-START
The LM2830 is a constant frequency PWM buck regulator IC
that delivers a 1.0A load current. The regulator has a preset
switching frequency of 1.6MHz or 3.0MHz. This high frequen-
cy allows the LM2830 to operate with small surface mount
capacitors and inductors, resulting in a DC/DC converter that
requires a minimum amount of board space. The LM2830 is
internally compensated, so it is simple to use and requires few
external components. The LM2830 uses current-mode con-
trol to regulate the output voltage. The following operating
description of the LM2830 will refer to the Simplified Block
Diagram (Figure 1) and to the waveforms in Figure 2. The
LM2830 supplies a regulated output voltage by switching the
internal PMOS control switch at constant frequency and vari-
able duty cycle. A switching cycle begins at the falling edge
of the reset pulse generated by the internal oscillator. When
this pulse goes low, the output control logic turns on the in-
ternal PMOS control switch. During this on-time, the SW pin
voltage (VSW) swings up to approximately VIN, and the induc-
tor current (IL) increases with a linear slope. IL is measured
by the current sense amplifier, which generates an output
proportional to the switch current. The sense signal is
summed with the regulator’s corrective ramp and compared
to the error amplifier’s output, which is proportional to the dif-
ference between the feedback voltage and VREF. When the
PWM comparator output goes high, the output switch turns
off until the next switching cycle begins. During the switch off-
time, inductor current discharges through the Schottky catch
diode, which forces the SW pin to swing below ground by the
forward voltage (VD) of the Schottky catch diode. The regu-
lator loop adjusts the duty cycle (D) to maintain a constant
output voltage.
This function forces VOUT to increase at a controlled rate dur-
ing start up. During soft-start, the error amplifier’s reference
voltage ramps from 0V to its nominal value of 0.6V in approx-
imately 600 µs. This forces the regulator output to ramp up in
a controlled fashion, which helps reduce inrush current.
OUTPUT OVERVOLTAGE PROTECTION
The over-voltage comparator compares the FB pin voltage to
a voltage that is 15% higher than the internal reference
VREF. Once the FB pin voltage goes 15% above the internal
reference, the internal PMOS control switch is turned off,
which allows the output voltage to decrease toward regula-
tion.
UNDERVOLTAGE LOCKOUT
Under-voltage lockout (UVLO) prevents the LM2830 from op-
erating until the input voltage exceeds 2.73V (typ). The UVLO
threshold has approximately 430 mV of hysteresis, so the part
will operate until VIN drops below 2.3V (typ). Hysteresis pre-
vents the part from turning off during power up if VIN is non-
monotonic.
CURRENT LIMIT
The LM2830 uses cycle-by-cycle current limiting to protect
the output switch. During each switching cycle, a current limit
comparator detects if the output switch current exceeds 1.75A
(typ), and turns off the switch until the next switching cycle
begins.
THERMAL SHUTDOWN
Thermal shutdown limits total power dissipation by turning off
the output switch when the IC junction temperature exceeds
165°C. After thermal shutdown occurs, the output switch
doesn’t turn on until the junction temperature drops to ap-
proximately 150°C.
20197466
FIGURE 2. Typical Waveforms
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10
age ripple. Now that the ripple current is determined, the
inductance is calculated by:
Design Guide
INDUCTOR SELECTION
The Duty Cycle (D) can be approximated quickly using the
ratio of output voltage (VO) to input voltage (VIN):
Where
The catch diode (D1) forward voltage drop and the voltage
drop across the internal PMOS must be included to calculate
a more accurate duty cycle. Calculate D by using the following
formula:
When selecting an inductor, make sure that it is capable of
supporting the peak output current without saturating. Induc-
tor saturation will result in a sudden reduction in inductance
and prevent the regulator from operating correctly. Because
of the speed of the internal current limit, the peak current of
the inductor need only be specified for the required maximum
output current. For example, if the designed maximum output
current is 1.0A and the peak current is 1.25A, then the induc-
tor should be specified with a saturation current limit of >
1.25A. There is no need to specify the saturation or peak cur-
rent of the inductor at the 1.75A typical switch current limit.
The difference in inductor size is a factor of 5. Because of the
operating frequency of the LM2830, ferrite based inductors
are preferred to minimize core losses. This presents little re-
striction since the variety of ferrite-based inductors is huge.
Lastly, inductors with lower series resistance (RDCR) will pro-
vide better operating efficiency. For recommended inductors
see Example Circuits.
VSW can be approximated by:
VSW = IOUT x RDSON
The diode forward drop (VD) can range from 0.3V to 0.7V de-
pending on the quality of the diode. The lower the VD, the
higher the operating efficiency of the converter. The inductor
value determines the output ripple current. Lower inductor
values decrease the size of the inductor, but increase the
output ripple current. An increase in the inductor value will
decrease the output ripple current.
One must ensure that the minimum current limit (1.2A) is not
exceeded, so the peak current in the inductor must be calcu-
lated. The peak current (ILPK) in the inductor is calculated by:
INPUT CAPACITOR
An input capacitor is necessary to ensure that VIN does not
drop excessively during switching transients. The primary
specifications of the input capacitor are capacitance, voltage,
RMS current rating, and ESL (Equivalent Series Inductance).
The recommended input capacitance is 22 µF.The input volt-
age rating is specifically stated by the capacitor manufacturer.
Make sure to check any recommended deratings and also
verify if there is any significant change in capacitance at the
operating input voltage and the operating temperature. The
ILPK = IOUT + ΔiL
input capacitor maximum RMS input current rating (IRMS-IN
must be greater than:
)
20197405
FIGURE 3. Inductor Current
Neglecting inductor ripple simplifies the above equation to:
In general,
It can be shown from the above equation that maximum RMS
capacitor current occurs when D = 0.5. Always calculate the
RMS at the point where the duty cycle D is closest to 0.5. The
ESL of an input capacitor is usually determined by the effec-
tive cross sectional area of the current path. A large leaded
capacitor will have high ESL and a 0805 ceramic chip capac-
itor will have very low ESL. At the operating frequencies of the
LM2830, leaded capacitors may have an ESL so large that
the resulting impedance (2πfL) will be higher than that re-
quired to provide stable operation. As a result, surface mount
capacitors are strongly recommended.
ΔiL = 0.1 x (IOUT) → 0.2 x (IOUT
)
If ΔiL = 20% of 1A, the peak current in the inductor will be 1.2A.
The minimum guaranteed current limit over all operating con-
ditions is 1.2A. One can either reduce ΔiL, or make the engi-
neering judgment that zero margin will be safe enough. The
typical current limit is 1.75A.
The LM2830 operates at frequencies allowing the use of ce-
ramic output capacitors without compromising transient re-
sponse. Ceramic capacitors allow higher inductor ripple
without significantly increasing output ripple. See the output
capacitor section for more details on calculating output volt-
Sanyo POSCAP, Tantalum or Niobium, Panasonic SP, and
multilayer ceramic capacitors (MLCC) are all good choices for
11
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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 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 VO and the FB pin. A good value for R2
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.
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:
VREF = 0.60V
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
VOUT trace to R2 should be routed away from the inductor and
any other traces that are switching. High AC currents flow
through the VIN, SW and VOUT traces, so they should be as
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.
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:
ID1 = IOUT x (1-D)
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.
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12
If the inductor ripple current is fairly small, the conduction
losses can be simplified to:
Calculating Efficiency, and Junction
Temperature
The complete LM2830 DC/DC converter efficiency can be
calculated in the following manner.
PCOND = IOUT2 x RDSON x D
Switching losses are also associated with the internal PFET.
They occur during the switch on and off transition periods,
where voltages and currents overlap resulting in power loss.
The simplest means to determine this loss is to empirically
measuring the rise and fall times (10% to 90%) of the switch
at the switch node.
Switching Power Loss is calculated as follows:
Or
PSWR = 1/2(VIN x IOUT x FSW x TRISE
)
PSWF = 1/2(VIN x IOUT x FSW x TFALL
PSW = PSWR + PSWF
)
Another loss is the power required for operation of the internal
circuitry:
Calculations for determining the most significant power loss-
es are shown below. Other losses totaling less than 2% are
not discussed.
PQ = IQ x VIN
IQ is the quiescent operating current, and is typically around
3.3mA for the 1.6MHz frequency option.
Power loss (PLOSS) is the sum of two basic types of losses in
the converter: switching and conduction. Conduction losses
usually dominate at higher output loads, whereas switching
losses remain relatively fixed and dominate at lower output
loads. The first step in determining the losses is to calculate
the duty cycle (D):
Typical Application power losses are:
Power Loss Tabulation
VIN
VOUT
IOUT
VD
5.0V
3.3V
POUT
3.3W
1.0A
0.45V
1.6MHz
3.3mA
4nS
PDIODE
150mW
FSW
IQ
VSW is the voltage drop across the internal PFET when it is
on, and is equal to:
PQ
PSWR
17mW
6mW
TRISE
TFALL
RDS(ON)
INDDCR
D
4nS
PSWF
6mW
VSW = IOUT x RDSON
PCOND
PIND
PLOSS
PINTERNAL
100mW
70mW
345mW
125mW
150mΩ
70mΩ
0.667
88%
VD is the forward voltage drop across the Schottky catch
diode. It can be obtained from the diode manufactures Elec-
trical Characteristics section. If the voltage drop across the
inductor (VDCR) is accounted for, the equation becomes:
η
ΣPCOND + PSW + PDIODE + PIND + PQ = PLOSS
ΣPCOND + PSWF + PSWR + PQ = PINTERNAL
PINTERNAL = 125mW
The conduction losses in the free-wheeling Schottky diode
are calculated as follows:
Thermal Definitions
TJ = Chip junction temperature
TA = Ambient temperature
PDIODE = VD x IOUT x (1-D)
RθJC = Thermal resistance from chip junction to device case
RθJA = Thermal resistance from chip junction to ambient air
Heat in the LM2830 due to internal power dissipation is re-
moved through conduction and/or convection.
Often this is the single most significant power loss in the cir-
cuit. Care should be taken to choose a Schottky diode that
has a low forward voltage drop.
Conduction: Heat transfer occurs through cross sectional ar-
eas of material. Depending on the material, the transfer of
heat can be considered to have poor to good thermal con-
ductivity properties (insulator vs. conductor).
Another significant external power loss is the conduction loss
in the output inductor. The equation can be simplified to:
PIND = IOUT2 x RDCR
Heat Transfer goes as:
The LM2830 conduction loss is mainly associated with the
internal PFET:
Silicon → package → lead frame → PCB
Convection: Heat transfer is by means of airflow. This could
be from a fan or natural convection. Natural convection occurs
when air currents rise from the hot device to cooler air.
Thermal impedance is defined as:
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junction temperature of 165°C. Knowing the internal power
dissipation from the above methods, the junction tempera-
ture, and the ambient temperature RθJA can be determined.
Thermal impedance from the silicon junction to the ambient
air is defined as:
Once this is determined, the maximum ambient temperature
allowed for a desired junction temperature can be found.
An example of calculating RθJA for an application using the
National Semiconductor LM2830 LLP demonstration board is
shown below.
The PCB size, weight of copper used to route traces and
ground plane, and number of layers within the PCB can great-
ly effect RθJA. The type and number of thermal vias can also
make a large difference in the thermal impedance. Thermal
vias are necessary in most applications. They conduct heat
from the surface of the PCB to the ground plane. Four to six
thermal vias should be placed under the exposed pad to the
ground plane if the LLP package is used.
The four layer PCB is constructed using FR4 with ½ oz copper
traces. The copper ground plane is on the bottom layer. The
ground plane is accessed by two vias. The board measures
3.0cm x 3.0cm. It was placed in an oven with no forced airflow.
The ambient temperature was raised to 144°C, and at that
temperature, the device went into thermal shutdown.
Thermal impedance also depends on the thermal properties
of the application operating conditions (Vin, Vo, Io etc), and
the surrounding circuitry.
From the previous example:
PINTERNAL = 189mW
Silicon Junction Temperature Determination Method 1:
To accurately measure the silicon temperature for a given
application, two methods can be used. The first method re-
quires the user to know the thermal impedance of the silicon
junction to top case temperature.
Some clarification needs to be made before we go any further.
RθJC is the thermal impedance from all six sides of an IC
package to silicon junction.
If the junction temperature was to be kept below 125°C, then
the ambient temperature could not go above 109°C
RΦJC is the thermal impedance from top case to the silicon
junction.
Tj - (RθJA x PLOSS) = TA
125°C - (111°C/W x 189mW) = 104°C
In this data sheet we will use RΦJC so that it allows the user
to measure top case temperature with a small thermocouple
attached to the top case.
LLP Package
RΦJC is approximately 30°C/Watt for the 6-pin LLP package
with the exposed pad. Knowing the internal dissipation from
the efficiency calculation given previously, and the case tem-
perature, which can be empirically measured on the bench
we have:
20197468
Therefore:
Tj = (RΦJC x PLOSS) + TC
From the previous example:
Tj = (RΦJC x PINTERNAL) + TC
Tj = 30°C/W x 0.189W + TC
FIGURE 4. Internal LLP Connection
For certain high power applications, the PCB land may be
modified to a "dog bone" shape (see Figure 6). By increasing
the size of ground plane, and adding thermal vias, the RθJA
for the application can be reduced.
The second method can give a very accurate silicon junction
temperature.
The first step is to determine RθJA of the application. The
LM2830 has over-temperature protection circuitry. When the
silicon temperature reaches 165°C, the device stops switch-
ing. The protection circuitry has a hysteresis of about 15°C.
Once the silicon temperature has decreased to approximately
150°C, the device will start to switch again. Knowing this, the
RθJA for any application can be characterized during the early
stages of the design one may calculate the RθJA by placing
the PCB circuit into a thermal chamber. Raise the ambient
temperature in the given working application until the circuit
enters thermal shutdown. If the SW-pin is monitored, it will be
obvious when the internal PFET stops switching, indicating a
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14
20197406
FIGURE 5. 6-Lead LLP PCB Dog Bone Layout
15
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LM2830X Design Example 1
20197407
FIGURE 6. LM2830X (1.6MHz): Vin = 5V, Vo = 1.2V @ 1.0A
Bill of Materials
Part ID
Part Value
Manufacturer
NSC
Part Number
LM2830X
U1
1.0A Buck Regulator
22µF, 6.3V, X5R
22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
3.3µH, 1.3A
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
C2, Output Cap
TDK
D1, Catch Diode
TOSHIBA
Coilcraft
Vishay
Vishay
Vishay
L1
R2
R1
R3
ME3220-332
CRCW08051502F
CRCW08051502F
CRCW08051003F
15.0kΩ, 1%
15.0kΩ, 1%
100kΩ, 1%
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16
LM2830X Design Example 2
20197460
FIGURE 7. LM2830X (1.6MHz): Vin = 5V, Vo = 0.6V @ 1.0A
Bill of Materials
Part ID
Part Value
Manufacturer
NSC
Part Number
LM2830X
U1
1.0A Buck Regulator
22µF, 6.3V, X5R
22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
3.3µH, 1.3A
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
C2, Output Cap
TDK
D1, Catch Diode
TOSHIBA
Coilcraft
Vishay
L1
R2
R1
R3
ME3220-332
CRCW08051000F
10.0kΩ, 1%
0Ω
Vishay
CRCW08051003F
100kΩ, 1%
17
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LM2830X Design Example 3
20197408
FIGURE 8. LM2830X (1.6MHz): Vin = 5V, Vo = 3.3V @ 1.0A
Bill of Materials
Part ID
Part Value
Manufacturer
NSC
Part Number
LM2830X
U1
1.0A Buck Regulator
22µF, 6.3V, X5R
22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
2.2µH, 1.8A
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
C2, Output Cap
TDK
D1, Catch Diode
TOSHIBA
Coilcraft
Vishay
Vishay
Vishay
L1
R2
R1
R3
ME3220-222
CRCW08051002F
CRCW08054532F
CRCW08051003F
10.0kΩ, 1%
45.3kΩ, 1%
100kΩ, 1%
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18
LM2830Z Design Example 4
20197408
FIGURE 9. LM2830Z (3MHz): Vin = 5V, Vo = 3.3V @ 1.0A
Bill of Materials
Part ID
Part Value
Manufacturer
NSC
Part Number
LM2830Z
U1
1.0A Buck Regulator
22µF, 6.3V, X5R
22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
1.6µH, 2.0A
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
C2, Output Cap
TDK
D1, Catch Diode
TOSHIBA
TDK
L1
R2
R1
R3
VLCF4018T-1R6N1R7-2
CRCW08051002F
CRCW08054532F
CRCW08051003F
Vishay
Vishay
Vishay
10.0kΩ, 1%
45.3kΩ, 1%
100kΩ, 1%
19
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LM2830Z Design Example 5
20197407
FIGURE 10. LM2830Z (3MHz): Vin = 5V, Vo = 1.2V @ 1.0A
Bill of Materials
Part ID
Part Value
Manufacturer
NSC
Part Number
LM2830Z
U1
1.0A Buck Regulator
22µF, 6.3V, X5R
22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
1.6µH, 2.0A
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
C2, Output Cap
TDK
D1, Catch Diode
TOSHIBA
TDK
L1
R2
R1
R3
VLCF4018T-1R6N1R7-2
CRCW08051002F
CRCW08051002F
CRCW08051003F
Vishay
Vishay
Vishay
10.0kΩ, 1%
10.0kΩ, 1%
100kΩ, 1%
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20
LM2830X Dual Converters with Delayed Enabled Design Example 6
20197462
FIGURE 11. LM2830X (1.6MHz): Vin = 5V, Vo = 1.2V @ 1.0A & 3.3V @1.0A
Bill of Materials
Part ID
U1, U2
Part Value
1.0A Buck Regulator
Power on Reset
22µF, 6.3V, X5R
22µF, 6.3V, X5R
Trr delay capacitor
0.3Vf Schottky 1.5A, 30VR
3.3µH, 1.3A
Manufacturer
NSC
Part Number
LM2830X
U3
NSC
LP3470M5X-3.08
C3216X5ROJ226M
C3216X5ROJ226M
C1, C3 Input Cap
C2, C4 Output Cap
C7
TDK
TDK
TDK
D1, D2 Catch Diode
L1, L2
TOSHIBA
Coilcraft
Vishay
Vishay
Vishay
CRS08
ME3220-332
R2, R4, R5
R1, R6
CRCW08051002F
CRCW08054532F
CRCW08051003F
10.0kΩ, 1%
45.3kΩ, 1%
R3
100kΩ, 1%
21
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LM2830X Buck Converter & Voltage Double Circuit with LDO Follower Design
Example 7
20197463
FIGURE 12. LM2830X (1.6MHz): Vin = 5V, Vo = 3.3V @ 1.0A & LP2986-5.0 @ 150mA
Bill of Materials
Part ID
Part Value
1.0A Buck Regulator
200mA LDO
Manufacturer
NSC
Part Number
LM2830X
U1
U2
NSC
LP2986-5.0
C1, Input Cap
22µF, 6.3V, X5R
22µF, 6.3V, X5R
2.2µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
0.4Vf Schottky 20VR, 500mA
10µH, 800mA
TDK
C3216X5ROJ226M
C3216X5ROJ226M
C1608X5R0J225M
CRS08
C2, Output Cap
TDK
C3 – C6
TDK
D1, Catch Diode
TOSHIBA
ON Semi
CoilCraft
TDK
D2
L2
L1
R2
R1
MBR0520
ME3220-103
3.3µH, 2.2A
VLCF5020T-3R3N2R0-1
CRCW08054532F
CRCW08051002F
Vishay
Vishay
45.3kΩ, 1%
10.0kΩ, 1%
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22
Physical Dimensions inches (millimeters) unless otherwise noted
5-Lead SOT-23 Package
NS Package Number MF05A
6-Lead LLP Package
NS Package Number SDE06A
23
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Notes
For more National Semiconductor product information and proven design tools, visit the following Web sites at:
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