LM2832YMY/NOPB [NSC]
IC 3.25 A SWITCHING REGULATOR, 700 kHz SWITCHING FREQ-MAX, PDSO8, EMSOP-8, Switching Regulator or Controller;
| 型号： | LM2832YMY/NOPB |
| 厂家： | 
National Semiconductor |
| 描述： | IC 3.25 A SWITCHING REGULATOR, 700 kHz SWITCHING FREQ-MAX, PDSO8, EMSOP-8, Switching Regulator or Controller 稳压器 |
| 文件： | 总27页 (文件大小：894K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
August 2006
LM2832
High Frequency 2.0A Load - Step-Down DC-DC
Regulator
General Description
Features
n Input voltage range of 3.0V to 5.5V
n Output voltage range of 0.6V to 4.5V
n 2.0A output current
The LM2832 regulator is a monolithic, high frequency, PWM
step-down DC/DC converter in a 6 Pin LLP and a 8 Pin
eMSOP package. It provides all the active functions to pro-
vide local DC/DC conversion with fast transient response
and accurate regulation in the smallest possible PCB area.
With a minimum of external components, the LM2832 is
easy to use. The ability to drive 2.0A loads with an internal
150 mΩ PMOS switch using state-of-the-art 0.5 µm BiCMOS
technology results in the best power density available. The
world-class control circuitry allows on-times as low as 30ns,
thus supporting exceptionally high frequency conversion
over the entire 3V to 5.5V input operating range down to the
minimum output voltage of 0.6V. Switching frequency is
internally set to 550 kHz, 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 shut-
down is included, featuring an ultra-low stand-by current of
30 nA. The LM2832 utilizes current-mode control and inter-
nal compensation to provide high-performance regulation
over a wide range of operating conditions. Additional fea-
tures include internal soft-start circuitry to reduce inrush
current, pulse-by-pulse current limit, thermal shutdown, and
output over-voltage protection.
n High Switching Frequencies
1.6MHz (LM2832X)
0.55MHz (LM2832Y)
3.0MHz (LM2832Z)
n 150mΩ PMOS switch
n 0.6V, 2% Internal Voltage Reference
n Internal soft-start
n Current mode, PWM operation
n Thermal Shutdown
n Over voltage protection
Applications
n Local 5V to Vcore Step-Down Converters
n Core Power in HDDs
n Set-Top Boxes
n USB Powered Devices
n DSL Modems
Typical Application Circuit
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20197581
© 2006 National Semiconductor Corporation
DS201975
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Connection Diagrams
20197501
20197502
6-Pin LLP
8-Pin eMSOP
Ordering Information
Frequency
Option
NSC Package
Drawing
Order Number
Package Type
eMSOP-8
LLP-6
Top Mark
SLBB
Supplied As
LM2832XMY
1000 units Tape and Reel
3500 units Tape and Reel
1000 units Tape and Reel
4500 units Tape and Reel
1000 units Tape and Reel
3500 units Tape and Reel
1000 units Tape and Reel
4500 units Tape and Reel
1000 units Tape and Reel
3500 units Tape and Reel
1000 units Tape and Reel
4500 units Tape and Reel
MUY08A
SDE06A
MUY08A
SDE06A
MUY08A
SDE06A
LM2832XMYX
1.6MHz
LM2832XSD
L196B
SLCB
LM2832XSDX
LM2832YMY
eMSOP-8
LLP-6
LM2832YMYX
0.55MHz
LM2832YSD
L197B
SLDB
LM2832YSDX
LM2832ZMY
eMSOP-8
LLP-6
LM2832ZMYX
3MHz
LM2832ZSD
L198B
LM2832ZSDX
NOPB versions available as well
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2
Pin Descriptions 8-Pin eMSOP
Pin
Name
VIND
VINA
GND
Function
1
2
Power Input supply.
Control circuitry supply voltage. Connect VINA to VIND on PC board.
Signal and power ground pin. Place the bottom resistor of the feedback network as close
as possible to this pin.
3, 5, 7
4
EN
Enable control input. Logic high enables operation. Do not allow this pin to float or be
greater
than VIN + 0.3V.
6
8
FB
SW
Feedback pin. Connect to external resistor divider to set output voltage.
Output switch. Connect to the inductor and catch diode.
Connect to system ground for low thermal impedance, but it cannot be used as a primary
GND connection.
DAP
Die Attach Pad
Pin Descriptions 6-Pin LLP
Pin
1
Name
FB
Function
Feedback pin. Connect to external resistor divider to set output voltage.
Signal and power ground pin. Place the bottom resistor of the feedback network as
close as possible to this pin.
2
GND
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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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Storage Temperature
Soldering Information
Infrared or Convection Reflow
(15 sec)
−65˚C to +150˚C
220˚C
VIN
-0.5V to 7V
-0.5V to 3V
-0.5V to 7V
-0.5V to 7V
2kV
FB Voltage
Operating Ratings
EN Voltage
VIN
3V to 5.5V
SW Voltage
Junction Temperature
−40˚C to +125˚C
ESD Susceptibility
Junction Temperature (Note 2)
150˚C
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
LLP-6 Package
Min
Typ
0.600
0.600
0.02
0.1
Max
0.612
0.616
Units
0.588
0.584
VFB
V
eMSOP-8 Package
VIN = 3V to 5V
∆VFB/VIN
Feedback Voltage Line Regulation
Feedback Input Bias Current
%/V
nA
V
IB
100
VIN Rising
2.73
2.3
2.90
Undervoltage Lockout
UVLO Hysteresis
UVLO
FSW
V
IN Falling
1.85
0.43
1.6
V
LM2832-X
1.2
0.4
2.25
86
1.95
0.7
Switching Frequency
Maximum Duty Cycle
LM2832-Y
0.55
3.0
MHz
LM2832-Z
3.75
LM2832-X
94
DMAX
LM2832-Y
90
96
%
%
LM2832-Z
82
90
LM2832-X
5
DMIN
Minimum Duty Cycle
Switch On Resistance
LM2832-Y
2
LM2832-Z
7
LLP-6 Package
eMSOP-8 Package
VIN = 3.3V
150
155
3.25
RDS(ON)
ICL
mΩ
A
240
0.4
Switch Current Limit
Shutdown Threshold Voltage
Enable Threshold Voltage
Switch Leakage
2.4
1.8
VEN_TH
V
ISW
IEN
100
100
3.3
2.8
4.3
30
nA
nA
Enable Pin Current
Sink/Source
LM2832X VFB = 0.55
LM2831Y VFB = 0.55
LM2832Z VFB = 0.55
All Options VEN = 0V
5
Quiescent Current (switching)
Quiescent Current (shutdown)
4.5
6.5
mA
nA
IQ
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4
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. (Continued)
Symbol
Parameter
Junction to Ambient
Conditions
LLP-6 and eMSOP-8
Packages
Min
Typ
Max
Units
80
θJA
˚C/W
0 LFPM Air Flow (Note 3)
Junction to Case (Note 3)
Thermal Shutdown Temperature
LLP-6 and eMSOP-8
Packages
18
θJC
˚C/W
˚C
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.
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Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical ap-
plication circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified.
η vs Load "X, Y and Z" Vin = 3.3V, Vo = 1.8V
η vs Load "X" Vin = 5V, Vo = 1.8V & 3.3V
20197587
20197539
η vs Load - "Y" Vin = 5V, Vo = 3.3V & 1.8V
η vs Load "Z" Vin = 5V, Vo = 3.3V & 1.8V
20197590
20197542
Load Regulation
Load Regulation
Vin = 3.3V, Vo = 1.8V (All Options)
Vin = 5V, Vo = 1.8V (All Options)
20197583
20197584
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6
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. (Continued)
Load Regulation
Vin = 5V, Vo = 3.3V (All Options)
Oscillator Frequency vs Temperature - "X"
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20197585
Oscillator Frequency vs Temperature - "Y"
Oscillator Frequency vs Temperature - "Z"
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20197525
Current Limit vs Temperature
Vin = 3.3V
RDSON vs Temperature (LLP-6 Package)
20197588
20197586
7
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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. (Continued)
RDSON vs Temperature (eMSOP-8 Package)
LM2832X IQ (Quiescent Current)
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20197528
LM2832Y IQ (Quiescent Current)
LM2832Z IQ (Quiescent Current)
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20197537
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8
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. (Continued)
Line Regulation
Vo = 1.8V, Io = 500mA
VFB vs Temperature
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20197553
Gain vs Frequency
Phase Plot vs Frequency
@
@
(Vin = 5V, Vo = 1.2V 1A)
(Vin = 5V, Vo = 1.2V 1A)
20197556
20197557
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Simplified Block Diagram
20197504
FIGURE 1.
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10
Applications Information
THEORY OF OPERATION
SOFT-START
The LM2832 is a constant frequency PWM buck regulator IC
that delivers a 2.0A load current. The regulator has a preset
switching frequency of 1.6MHz or 3.0MHz. This high fre-
quency allows the LM2832 to operate with small surface
mount capacitors and inductors, resulting in a DC/DC con-
verter that requires a minimum amount of board space. The
LM2832 is internally compensated, so it is simple to use and
requires few external components. The LM2832 uses
current-mode control to regulate the output voltage. The
following operating description of the LM2832 will refer to the
Simplified Block Diagram (Figure 1) and to the waveforms in
Figure 2. The LM2832 supplies a regulated output voltage by
switching the internal PMOS control switch at constant fre-
quency and variable 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 internal PMOS control switch. During this on-
time, the SW pin voltage (VSW) swings up to approximately
VIN, and the inductor 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 pro-
portional to the difference 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 regulator loop adjusts the duty
cycle (D) to maintain a constant output voltage.
This function forces VOUT to increase at a controlled rate
during start up. During soft-start, the error amplifier’s refer-
ence voltage ramps from 0V to its nominal value of 0.6V in
approximately 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 LM2832 from
operating 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). Hys-
teresis prevents the part from turning off during power up if
VIN is non-monotonic.
CURRENT LIMIT
The LM2832 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
3.25A (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 ex-
ceeds 165˚C. After thermal shutdown occurs, the output
switch doesn’t turn on until the junction temperature drops to
approximately 150˚C.
20197566
FIGURE 2. Typical Waveforms
11
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capacitor section for more details on calculating output volt-
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 follow-
ing 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 maxi-
mum output current. For example, if the designed maximum
output current is 1.0A and the peak current is 1.25A, then the
inductor should be specified with a saturation current limit of
VSW can be approximated by:
VSW = IOUT x RDSON
The diode forward drop (VD) can range from 0.3V to 0.7V
depending 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.
>
1.25A. There is no need to specify the saturation or peak
current of the inductor at the 3.25A typical switch current
limit. The difference in inductor size is a factor of 5. Because
of the operating frequency of the LM2832, ferrite based
inductors are preferred to minimize core losses. This pre-
sents little restriction since the variety of ferrite-based induc-
tors is huge. Lastly, inductors with lower series resistance
(RDCR) will provide better operating efficiency. For recom-
mended inductors see Example Circuits.
One must ensure that the minimum current limit (2.4A) is not
exceeded, so the peak current in the inductor must be
calculated. The peak current (ILPK) in the inductor is calcu-
lated 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, volt-
age, RMS current rating, and ESL (Equivalent Series Induc-
tance). The recommended input capacitance is 22 µF.The
input voltage rating is specifically stated by the capacitor
manufacturer. Make sure to check any recommended derat-
ings and also verify if there is any significant change in
capacitance at the operating input voltage and the operating
temperature. The input capacitor maximum RMS input cur-
rent rating (IRMS-IN) must be greater than:
ILPK = IOUT + ∆iL
20197505
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 calcu-
late 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 effective cross sectional area of the current path. A large
leaded capacitor will have high ESL and a 0805 ceramic chip
capacitor will have very low ESL. At the operating frequen-
cies of the LM2832, leaded capacitors may have an ESL so
large that the resulting impedance (2πfL) will be higher than
that required to provide stable operation. As a result, surface
mount capacitors are strongly recommended.
→
0.2 x (IOUT)
∆iL = 0.1 x (IOUT
)
If ∆iL = 20% of 2A, the peak current in the inductor will be
2.4A. The minimum guaranteed current limit over all operat-
ing conditions is 2.4A. One can either reduce ∆iL, or make
the engineering judgment that zero margin will be safe
enough. The typical current limit is 3.25A.
The LM2832 operates at frequencies allowing the use of
ceramic output capacitors without compromising transient
response. Ceramic capacitors allow higher inductor ripple
without significantly increasing output ripple. See the output
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12
OUTPUT VOLTAGE
Design Guide (Continued)
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.
Sanyo POSCAP, Tantalum or Niobium, Panasonic SP, and
multilayer ceramic capacitors (MLCC) are all good choices
for 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 character-
istics. Consult capacitor manufacturer datasheets to see
how rated capacitance varies over operating conditions.
OUTPUT CAPACITOR
The output capacitor is selected based upon the desired
output ripple and transient response. The initial current of a
load transient is provided mainly by the output capacitor. The
output 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
important consideration is the close coupling of the GND
connections of the input capacitor and the catch diode D1.
These ground ends should be close to one another and be
connected to the GND plane with at least two through-holes.
Place these components as close to the IC as possible. Next
in importance 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 resis-
tors 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 LM2832 demo board as an example of a four-layer
layout.
When using MLCCs, the ESR is typically so low that the
capacitive ripple may dominate. When this occurs, the out-
put 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 LM2832, there is really no need to review any other
capacitor technologies. Another benefit of ceramic capaci-
tors is their ability to bypass high frequency noise. A certain
amount of switching edge noise will couple through parasitic
capacitances in the inductor to the output. A ceramic capaci-
tor 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 appli-
cations will require a minimum of 22 µF of output capaci-
tance. Capacitance often, but not always, can be increased
significantly with little detriment to the regulator stability. Like
the input capacitor, recommended multilayer ceramic ca-
pacitors 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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2
PCOND = IOUT x RDSON x D
Calculating Efficiency, and
Junction Temperature
The complete LM2832 DC/DC converter efficiency can be
calculated in the following manner.
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:
PSWR = 1/2(VIN x IOUT x FSW x TRISE
)
PSWF = 1/2(VIN x IOUT x FSW x TFALL
)
Or
PSW = PSWR + PSWF
Another loss is the power required for operation of the inter-
nal circuitry:
PQ = IQ x VIN
IQ is the quiescent operating current, and is typically around
2.5mA for the 0.55MHz frequency option.
Calculations for determining the most significant power
losses are shown below. Other losses totaling less than 2%
are not discussed.
Typical Application power losses are:
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):
Power Loss Tabulation
VIN
VOUT
IOUT
VD
5.0V
3.3V
POUT
5.78W
1.75A
0.45V
550kHz
2.5mA
4nS
PDIODE
262mW
FSW
IQ
PQ
PSWR
12.5mW
10mW
TRISE
TFALL
RDS(ON)
INDDCR
D
VSW is the voltage drop across the internal PFET when it is
on, and is equal to:
4nS
PSWF
10mW
150mΩ
50mΩ
0.667
88%
PCOND
PIND
PLOSS
PINTERNAL
306mW
153mW
753mW
339mW
VSW = IOUT x RDSON
η
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:
ΣPCOND + PSW + PDIODE + PIND + PQ = PLOSS
ΣPCOND + PSWF + PSWR + PQ = PINTERNAL
PINTERNAL = 339mW
Thermal Definitions
TJ = Chip junction temperature
TA = Ambient temperature
The conduction losses in the free-wheeling Schottky diode
are calculated as follows:
RθJC = Thermal resistance from chip junction to device case
RθJA = Thermal resistance from chip junction to ambient air
PDIODE = VD x IOUT x (1-D)
Heat in the LM2832 due to internal power dissipation is
removed through conduction and/or convection.
Conduction: Heat transfer occurs through cross sectional
areas 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).
Often this is the single most significant power loss in the
circuit. Care should be taken to choose a Schottky diode that
has a low forward voltage drop.
Another significant external power loss is the conduction
loss in the output inductor. The equation can be simplified to:
Heat Transfer goes as:
2
→
→
→
lead frame PCB
Silicon
package
PIND = IOUT x RDCR
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.
The LM2832 conduction loss is mainly associated with the
internal PFET:
Thermal impedance is defined as:
If the inductor ripple current is fairly small, the conduction
losses can be simplified to:
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ambient temperature in the given working application until
the circuit enters thermal shutdown. If the SW-pin is moni-
tored, it will be obvious when the internal PFET stops switch-
ing, indicating a junction temperature of 165˚C. Knowing the
internal power dissipation from the above methods, the junc-
tion temperature, and the ambient temperature RθJA can be
determined.
Thermal Definitions (Continued)
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.
The PCB size, weight of copper used to route traces and
ground plane, and number of layers within the PCB can
greatly 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 con-
duct 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.
An example of calculating RθJA for an application using the
National Semiconductor LM2832 LLP demonstration board
is shown below.
1
The four layer PCB is constructed using FR4 with
⁄2 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
126˚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:
Silicon Junction Temperature Determination Method 1:
To accurately measure the silicon temperature for a given
application, two methods can be used. The first method
requires the user to know the thermal impedance of the
silicon junction to top case temperature.
PINTERNAL = 339mW
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 86˚C.
RΦJC is the thermal impedance from top case to the silicon
junction.
Tj - (RθJA x PLOSS) = TA
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.
125˚C - (115˚C/W x 339mW) = 86˚C
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
temperature, which can be empirically measured on the
bench we have:
Therefore:
20197568
Tj = (RΦJC x PLOSS) + TC
From the previous example:
Tj = (RΦJC x PINTERNAL) + TC
Tj = 30˚C/W x 0.339W + 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
LM2832 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 approxi-
mately 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
15
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LLP Package (Continued)
20197506
FIGURE 5. 6-Lead LLP PCB Dog Bone Layout
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16
LM2832X Design Example 1
20197507
@
FIGURE 6. LM2832X (1.6MHz): Vin = 5V, Vo = 1.2V 2.0A
Bill of Materials
Part ID
Part Value
2.0A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.4Vf Schottky 2A, 20VR
2.2µH, 3.5A
Manufacturer
NSC
Part Number
LM2832X
U1
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
B220/A
C2, Output Cap
TDK
D1, Catch Diode
Diodes Inc.
Coilcraft
Vishay
L1
R2
R1
R3
DS3316P-222
15.0kΩ, 1%
CRCW08051502F
CRCW08051502F
CRCW08051003F
15.0kΩ, 1%
Vishay
100kΩ, 1%
Vishay
17
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LM2832X Design Example 2
20197560
@
FIGURE 7. LM2832X (1.6MHz): Vin = 5V, Vo = 0.6V 2.0A
Bill of Materials
Part ID
Part Value
2.0A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.4Vf Schottky 2A, 20VR
3.3µH, 3.3A
Manufacturer
NSC
Part Number
LM2832X
U1
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
B220/A
C2, Output Cap
TDK
D1, Catch Diode
Diodes Inc.
Coilcraft
Vishay
L1
R2
R1
R3
DS3316P-332
CRCW08051000F
10.0kΩ, 1%
0Ω
100kΩ, 1%
Vishay
CRCW08051003F
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18
LM2832X Design Example 3
20197508
@
FIGURE 8. LM2832X (1.6MHz): Vin = 5V, Vo = 3.3V 2.0A
Bill of Materials
Part ID
Part Value
2.0A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.4Vf Schottky 2A, 20VR
2.2µH, 2.8A
Manufacturer
NSC
Part Number
LM2832X
U1
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
B220/A
C2, Output Cap
TDK
D1, Catch Diode
Diodes Inc.
Coilcraft
Vishay
L1
R2
R1
R3
ME3220-222
10.0kΩ, 1%
CRCW08051002F
CRCW08054532F
CRCW08051003F
45.3kΩ, 1%
Vishay
100kΩ, 1%
Vishay
19
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LM2832Y Design Example 4
20197508
@
FIGURE 9. LM2832Y (550kHz): Vin = 5V, Vout = 3.3V 2.0A
Bill of Materials
Part ID
Part Value
1.5A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
4.7µH 2.1A
Manufacturer
NSC
Part Number
LM2832Y
U1
C1, Input Cap
C2, Output Cap
D1, Catch Diode
L1
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
TDK
TOSHIBA
TDK
SLF7045T-4R7M2R0-PF
CRCW08051002F
CRCW08051002F
R1
10.0kΩ, 1%
Vishay
Vishay
R2
10.0kΩ, 1%
www.national.com
20
LM2832Y Design Example 5
20197507
@
FIGURE 10. LM2832Y (550kHz): Vin = 5V, Vout = 1.2V 2.0A
Bill of Materials
Part ID
Part Value
1.5A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.3Vf Schottky 1.5A, 30VR
6.8µH 1.8A
Manufacturer
NSC
Part Number
LM2832Y
U1
C1, Input Cap
C2, Output Cap
D1, Catch Diode
L1
TDK
C3216X5ROJ226M
C3216X5ROJ226M
CRS08
TDK
TOSHIBA
TDK
SLF7045T-6R8M1R7
CRCW08051002F
CRCW08051002F
R1
10.0kΩ, 1%
Vishay
Vishay
R2
10.0kΩ, 1%
21
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LM2832Z Design Example 6
20197508
@
FIGURE 11. LM2832Z (3MHz): Vin = 5V, Vo = 3.3V 2.0A
Bill of Materials
Part ID
Part Value
2.0A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.4Vf Schottky 2A, 20VR
3.3µH, 3.3A
Manufacturer
NSC
Part Number
LM2832Z
U1
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
B220/A
C2, Output Cap
TDK
D1, Catch Diode
Diodes Inc.
Coilcraft
Vishay
L1
R2
R1
R3
DS3316P-332
10.0kΩ, 1%
CRCW08051002F
CRCW08054532F
CRCW08051003F
45.3kΩ, 1%
Vishay
100kΩ, 1%
Vishay
www.national.com
22
LM2832Z Design Example 7
20197507
@
FIGURE 12. LM2832Z (3MHz): Vin = 5V, Vo = 1.2V 2.0A
Bill of Materials
Part ID
Part Value
2.0A Buck Regulator
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
0.4Vf Schottky 2A, 20VR
4.7µH, 2.7A
Manufacturer
NSC
Part Number
LM2832Z
U1
C1, Input Cap
TDK
C3216X5ROJ226M
C3216X5ROJ226M
B220/A
C2, Output Cap
TDK
D1, Catch Diode
Diodes Inc.
Coilcraft
Vishay
L1
R2
R1
R3
DS3316P-472
10.0kΩ, 1%
CRCW08051002F
CRCW08051002F
CRCW08051003F
10.0kΩ, 1%
Vishay
100kΩ, 1%
Vishay
23
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LM2832X Dual Converters with Delayed Enabled Design Example 8
20197562
@
@
FIGURE 13. LM2832X (1.6MHz): Vin = 5V, Vo = 1.2V 2.0A & 3.3V 2.0A
Bill of Materials
Part ID
U1, U2
Part Value
2.0A Buck Regulator
Power on Reset
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
Trr delay capacitor
0.4Vf Schottky 2A, 20VR
3.3µH, 2.7A
Manufacturer
NSC
Part Number
LM2832X
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
Diodes Inc.
Coilcraft
Vishay
Vishay
Vishay
B220/A
ME3220-102
R2, R4, R5
R1, R6
10.0kΩ, 1%
CRCW08051002F
CRCW08054532F
CRCW08051003F
45.3kΩ, 1%
R3
100kΩ, 1%
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24
LM2832X Buck Converter & Voltage Double Circuit with LDO Follower
Design Example 9
20197563
@
@
FIGURE 14. LM2832X (1.6MHz): Vin = 5V, Vo = 3.3V 2.0A & LP2986-5.0 150mA
Bill of Materials
Part ID
Part Value
2.0A Buck Regulator
200mA LDO
Manufacturer
NSC
Part Number
U1
LM2832X
LP2986-5.0
U2
NSC
C1, Input Cap
22µF, 6.3V, X5R
2x22µF, 6.3V, X5R
2.2µF, 6.3V, X5R
0.4Vf Schottky 2A, 20VR
0.4Vf Schottky 20VR, 500mA
10µH, 800mA
TDK
C3216X5ROJ226M
C3216X5ROJ226M
C1608X5R0J225M
B220/A
C2, Output Cap
TDK
C3 – C6
TDK
D1, Catch Diode
Diodes Inc.
ON Semi
CoilCraft
CoilCraft
Vishay
D2
L2
L1
R2
R1
MBR0520
ME3220-103
2.2µH, 3.5A
DS3316P-222
CRCW08054532F
CRCW08051002F
45.3kΩ, 1%
10.0kΩ, 1%
Vishay
25
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Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead eMSOP Package
NS Package Number MUY08A
6-Lead LLP Package
NS Package Number SDE06A
www.national.com
26
Notes
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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(b) support or sustain life, and whose failure to perform when
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