LM2832
High Frequency 2.0A Load - Step-Down DC-DC
Regulator
LM2832 High Frequency 2.0A Load - Step-Down DC-DC Regulator
August 2006
General Description
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 provide 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 shutdown is included, featuring an ultra-low stand-by current of
30 nA. The LM2832 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 circuitry to reduce inrush
current, pulse-by-pulse current limit, thermal shutdown, and
output over-voltage protection.
Typical Application Circuit
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
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
20197564
© 2006 National Semiconductor Corporation DS201975 www.national.com
20197581
Connection Diagrams
LM2832
6-Pin LLP
20197501
8-Pin eMSOP
20197502
Ordering Information
Order Number
LM2832XMY
LM2832XMYX 3500 units Tape and Reel
LM2832XSD
LM2832XSDX 4500 units Tape and Reel
LM2832YMY
LM2832YMYX 3500 units Tape and Reel
LM2832YSD
LM2832YSDX 4500 units Tape and Reel
LM2832ZMY
LM2832ZMYX 3500 units Tape and Reel
LM2832ZSD
LM2832ZSDX 4500 units Tape and Reel
NOPB versions available as well
Frequency
Option
1.6MHz
0.55MHz
3MHz
Package Type
eMSOP-8 MUY08A SLBB
LLP-6 SDE06A L196B
eMSOP-8 MUY08A SLCB
LLP-6 SDE06A L197B
eMSOP-8 MUY08A SLDB
LLP-6 SDE06A L198B
NSC Package
Drawing
Top Mark Supplied As
1000 units Tape and Reel
1000 units Tape and Reel
1000 units Tape and Reel
1000 units Tape and Reel
1000 units Tape and Reel
1000 units Tape and Reel
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Pin Descriptions 8-Pin eMSOP
Pin Name Function
1 VIND Power Input supply.
2 VINA Control circuitry supply voltage. Connect VINA to VIND on PC board.
3, 5, 7 GND Signal and power ground pin. Place the bottom resistor of the feedback network as close
as possible to this pin.
4 EN Enable control input. Logic high enables operation. Do not allow this pin to float or be
greater
than VIN + 0.3V.
6 FB Feedback pin. Connect to external resistor divider to set output voltage.
8 SW Output switch. Connect to the inductor and catch diode.
DAP Die Attach Pad Connect to system ground for low thermal impedance, but it cannot be used as a primary
GND connection.
Pin Descriptions 6-Pin LLP
Pin Name Function
1 FB 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 SW Output switch. Connect to the inductor and catch diode.
4 VIND Power Input supply.
5 VINA Control circuitry supply voltage. Connect VINA to VIND on PC board.
6 EN 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.
LM2832
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
LM2832
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Storage Temperature −65˚C to +150˚C
Soldering Information
Infrared or Convection Reflow
(15 sec) 220˚C
VIN -0.5V to 7V
FB Voltage -0.5V to 3V
Operating Ratings
EN Voltage -0.5V to 7V
SW Voltage -0.5V to 7V
ESD Susceptibility 2kV
VIN 3V to 5.5V
Junction Temperature −40˚C to +125˚C
Junction Temperature (Note 2) 150˚C
Electrical Characteristics VIN = 5V unless otherwise indicated under the Conditions column. Limits in
standard type are for T
+125˚C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent
the most likely parametric norm at T
Symbol Parameter Conditions Min Typ Max Units
∆V
UVLO
V
FB
FB/VIN
I
B
Feedback Voltage
Feedback Voltage Line Regulation VIN= 3V to 5V 0.02 %/V
Feedback Input Bias Current 0.1 100 nA
Undervoltage Lockout
UVLO Hysteresis 0.43 V
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
Switch On Resistance
Switch Current Limit VIN= 3.3V 2.4 3.25 A
Shutdown Threshold Voltage 0.4
Enable Threshold Voltage 1.8
Switch Leakage 100 nA
Enable Pin Current Sink/Source 100 nA
Quiescent Current (switching)
D
R
V
F
SW
MAX
D
MIN
DS(ON)
I
CL
EN_TH
I
SW
I
EN
I
Q
Quiescent Current (shutdown) All Options V
= 25˚C only; limits in boldface type apply over the junction temperature (TJ) range of -40˚C to
J
= 25˚C, and are provided for reference purposes only.
J
LLP-6 Package 0.588 0.600 0.612
eMSOP-8 Package 0.584 0.600 0.616
Rising 2.73 2.90 V
V
IN
V
Falling 1.85 2.3
IN
LM2832-X 1.2 1.6 1.95
LM2832-Z 2.25 3.0 3.75
LM2832-X 86 94
LM2832-Z 82 90
LM2832-X 5
LM2832-Z 7
LLP-6 Package 150
eMSOP-8 Package 155 240
LM2832X V
LM2832Z V
= 0.55 3.3 5
FB
= 0.55 2.8 4.5
FB
= 0.55 4.3 6.5
FB
=0V 30 nA
EN
V
MHzLM2832-Y 0.4 0.55 0.7
%LM2832-Y 90 96
%LM2832-Y 2
mΩ
V
mALM2831Y V
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Electrical Characteristics VIN = 5V unless otherwise indicated under the Conditions column. Limits in
standard type are for T
+125˚C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent
the most likely parametric norm at T
Symbol Parameter Conditions Min Typ Max Units
θ
JA
θ
JC
T
SD
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.
Junction to Ambient
0 LFPM Air Flow (Note 3)
Junction to Case (Note 3)
Thermal Shutdown Temperature 165 ˚C
= 25˚C only; limits in boldface type apply over the junction temperature (TJ) range of -40˚C to
J
= 25˚C, and are provided for reference purposes only. (Continued)
J
LLP-6 and eMSOP-8
80
Packages
LLP-6 and eMSOP-8
18
Packages
˚C/W
˚C/W
LM2832
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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. T
LM2832
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
= 25˚C, unless otherwise specified.
J
20197590 20197542
Load Regulation
Vin = 3.3V, Vo = 1.8V (All Options)
20197583 20197584
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Load Regulation
Vin = 5V, Vo = 1.8V (All Options)
Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical
application circuit shown in Application Information section of this datasheet. T
specified. (Continued)
Load Regulation
Vin = 5V, Vo = 3.3V (All Options) Oscillator Frequency vs Temperature - "X"
= 25˚C, unless otherwise
J
LM2832
20197585
20197524
Oscillator Frequency vs Temperature - "Y" Oscillator Frequency vs Temperature - "Z"
20197525
20197536
Current Limit vs Temperature
Vin = 3.3V RDSON vs Temperature (LLP-6 Package)
20197586
20197588
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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. T
LM2832
specified. (Continued)
= 25˚C, unless otherwise
J
RDSON vs Temperature (eMSOP-8 Package) LM2832X I
20197589
(Quiescent Current)
Q
LM2832Y IQ(Quiescent Current) LM2832Z IQ(Quiescent Current)
20197528
20197529
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20197537
Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical
application circuit shown in Application Information section of this datasheet. T
specified. (Continued)
Line Regulation
Vo = 1.8V, Io = 500mA V
= 25˚C, unless otherwise
J
vs Temperature
FB
LM2832
Gain vs Frequency
(Vin = 5V, Vo = 1.2V
20197553
20197527
Phase Plot vs Frequency
@
1A)
20197556 20197557
(Vin = 5V, Vo = 1.2V@1A)
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Simplified Block Diagram
LM2832
FIGURE 1.
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20197504
Applications Information
THEORY OF OPERATION
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 frequency allows the LM2832 to operate with small surface
mount capacitors and inductors, resulting in a DC/DC converter 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 frequency 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 ontime, the SW pin voltage (V
, and the inductor current (IL) increases with a linear
V
IN
slope. I
is measured by the current sense amplifier, which
L
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 difference between the feedback voltage and
. When the PWM comparator output goes high, the
V
REF
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 (V
Schottky catch diode. The regulator loop adjusts the duty
cycle (D) to maintain a constant output voltage.
) swings up to approximately
SW
)ofthe
D
SOFT-START
This function forces V
to increase at a controlled rate
OUT
during start up. During soft-start, the error amplifier’s reference 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
. Once the FB pin voltage goes 15% above the internal
V
REF
reference, the internal PMOS control switch is turned off,
which allows the output voltage to decrease toward regulation.
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 V
drops below 2.3V (typ). Hys-
IN
teresis prevents the part from turning off during power up if
is non-monotonic.
V
IN
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 exceeds 165˚C. After thermal shutdown occurs, the output
switch doesn’t turn on until the junction temperature drops to
approximately 150˚C.
LM2832
FIGURE 2. Typical Waveforms
20197566
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Design Guide
LM2832
INDUCTOR SELECTION
The Duty Cycle (D) can be approximated quickly using the
ratio of output voltage (V
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:
VSWcan be approximated by:
The diode forward drop (VD) can range from 0.3V to 0.7V
depending on the quality of the diode. The lower the V
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 (2.4A) is not
exceeded, so the peak current in the inductor must be
calculated. The peak current (I
lated by:
) to input voltage (VIN):
O
V
SW=IOUTxRDSON
LPK
I
LPK=IOUT
+ ∆i
) in the inductor is calcu-
L
D
, the
20197505
capacitor section for more details on calculating output voltage ripple. Now that the ripple current is determined, the
inductance is calculated by:
Where
When selecting an inductor, make sure that it is capable of
supporting the peak output current without saturating. Inductor 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
inductor should be specified with a saturation current limit of
>
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 presents little restriction since the variety of ferrite-based inductors is huge. Lastly, inductors with lower series resistance
) will provide better operating efficiency. For recom-
(R
DCR
mended inductors see Example Circuits.
INPUT CAPACITOR
An input capacitor is necessary to ensure that V
does not
IN
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 voltage 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 input capacitor maximum RMS input current rating (I
) must be greater than:
RMS-IN
FIGURE 3. Inductor Current
In general,
∆i
=0.1x(I
L
= 20% of 2A, the peak current in the inductor will be
If ∆i
L
)→0.2x(I
OUT
OUT
)
2.4A. The minimum guaranteed current limit over all operating conditions is 2.4A. One can either reduce ∆i
, or make
L
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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Neglecting inductor ripple simplifies the above equation to:
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 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 frequencies 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.
Design Guide (Continued)
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 characteristics. 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:
When using MLCCs, the ESR is typically so low that the
capacitive 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 LM2832, 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
capacitances 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. Capacitance often, but not always, can be increased
significantly with little detriment to the regulator stability. Like
the input capacitor, 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:
I
D1=IOUT
The reverse breakdown rating of the diode must be at least
the maximum input voltage plus appropriate margin. To improve efficiency, choose a Schottky diode with a low forward
voltage drop.
x (1-D)
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
and the FB pin. A good value for R2
O
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.
V
= 0.60V
REF
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 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
trace to R2 should be routed away from the
OUT
inductor and any other traces that are switching. High AC
currents flow through the V
, SW and V
IN
traces, so they
OUT
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.
LM2832
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Calculating Efficiency, and Junction Temperature
LM2832
The complete LM2832 DC/DC converter efficiency can be
calculated in the following manner.
Or
Calculations for determining the most significant power
losses are shown below. Other losses totaling less than 2%
are not discussed.
Power loss (P
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):
VSWis the voltage drop across the internal PFET when it is
on, and is equal to:
VDis the forward voltage drop across the Schottky catch
diode. It can be obtained from the diode manufactures Electrical Characteristics section. If the voltage drop across the
inductor (V
) is the sum of two basic types of losses in
LOSS
V
SW=IOUTxRDSON
) is accounted for, the equation becomes:
DCR
P
COND=IOUT
2
xR
DSON
xD
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:
P
SWR
P
SWF
= 1/2(VINxI
= 1/2(VINxI
P
SW=PSWR+PSWF
OUTxFSWxTRISE
OUTxFSWxTFALL
)
)
Another loss is the power required for operation of the internal circuitry:
P
Q=IQxVIN
IQis the quiescent operating current, and is typically around
2.5mA for the 0.55MHz frequency option.
Typical Application power losses are:
Power Loss Tabulation
V
IN
V
OUT
I
OUT
V
D
F
SW
I
Q
T
RISE
T
FALL
R
DS(ON)
IND
DCR
D 0.667 P
η 88% P
ΣP
COND+PSW+PDIODE+PIND+PQ=PLOSS
ΣP
COND
5.0V
3.3V P
OUT
1.75A
0.45V P
DIODE
550kHz
2.5mA P
4nS P
4nS P
150mΩ P
50mΩ P
+P
SWF+PSWR+PQ=PINTERNAL
P
INTERNAL
Q
SWR
SWF
COND
IND
LOSS
INTERNAL
= 339mW
5.78W
262mW
12.5mW
10mW
10mW
306mW
153mW
753mW
339mW
The conduction losses in the free-wheeling Schottky diode
are calculated as follows:
P
DIODE
=VDxI
OUT
x (1-D)
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:
2
P
IND=IOUT
xR
DCR
The LM2832 conduction loss is mainly associated with the
internal PFET:
If the inductor ripple current is fairly small, the conduction
losses can be simplified to:
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Thermal Definitions
TJ= Chip junction temperature
T
= Ambient temperature
A
= Thermal resistance from chip junction to device case
R
θJC
= Thermal resistance from chip junction to ambient air
R
θJA
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 conductivity properties (insulator vs. conductor).
Heat Transfer goes as:
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:
Thermal Definitions (Continued)
Thermal impedance from the silicon junction to the ambient
air is defined as:
The PCB size, weight of copper used to route traces and
ground plane, and number of layers within the PCB can
greatly effect R
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.
Thermal impedance also depends on the thermal properties
of the application operating conditions (Vin, Vo, Io etc), and
the surrounding circuitry.
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.
Some clarification needs to be made before we go any
further.
is the thermal impedance from all six sides of an IC
R
θJC
package to silicon junction.
is the thermal impedance from top case to the silicon
R
ΦJC
junction.
In this data sheet we will use R
to measure top case temperature with a small thermocouple
attached to the top case.
is approximately 30˚C/Watt for the 6-pin LLP package
R
ΦJC
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:
. The type and number of thermal vias can
θJA
so that it allows the user
ΦJC
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 junction temperature of 165˚C. Knowing the
internal power dissipation from the above methods, the junction temperature, and the ambient temperature R
θJA
can be
determined.
Once this is determined, the maximum ambient temperature
allowed for a desired junction temperature can be found.
An example of calculating R
for an application using the
θJA
National Semiconductor LM2832 LLP demonstration board
is shown below.
1
The four layer PCB is constructed using FR4 with
⁄2oz
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.
From the previous example:
P
INTERNAL
= 339mW
If the junction temperature was to be kept below 125˚C, then
the ambient temperature could not go above 86˚C.
T
j
-(R
θJAxPLOSS
)=T
A
125˚C - (115˚C/W x 339mW) = 86˚C
LLP Package
LM2832
Therefore:
T
j
=(R
ΦJCxPLOSS
)+T
C
From the previous example:
=(R
T
j
ΦJCxPINTERNAL
Tj= 30˚C/W x 0.339W + T
)+T
C
C
The second method can give a very accurate silicon junction
temperature.
The first step is to determine R
of the application. The
θJA
LM2832 has over-temperature protection circuitry. When the
silicon temperature reaches 165˚C, the device stops switching. 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 R
the early stages of the design one may calculate the R
for any application can be characterized during
θJA
θJA
by
placing the PCB circuit into a thermal chamber. Raise the
20197568
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 R
θJA
for the application can be reduced.
www.national.com15
LLP Package (Continued)
LM2832
FIGURE 5. 6-Lead LLP PCB Dog Bone Layout
20197506
www.national.com 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 Manufacturer Part Number
U1 2.0A Buck Regulator NSC LM2832X
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.4V
L1 2.2µH, 3.5A Coilcraft DS3316P-222
R2 15.0kΩ, 1% Vishay CRCW08051502F
R1 15.0kΩ, 1% Vishay CRCW08051502F
R3 100kΩ, 1% Vishay CRCW08051003F
Schottky 2A, 20V
f
R
Diodes Inc. B220/A
LM2832
www.national.com17
LM2832X Design Example 2
LM2832
Part ID Part Value Manufacturer Part Number
U1 2.0A Buck Regulator NSC LM2832X
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.4V
L1 3.3µH, 3.3A Coilcraft DS3316P-332
R2 10.0kΩ, 1% Vishay CRCW08051000F
R1 0Ω
R3 100kΩ, 1% Vishay CRCW08051003F
FIGURE 7. LM2832X (1.6MHz): Vin = 5V, Vo = 0.6V@2.0A
Bill of Materials
Schottky 2A, 20V
f
R
Diodes Inc. B220/A
20197560
www.national.com 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 Manufacturer Part Number
U1 2.0A Buck Regulator NSC LM2832X
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.4V
L1 2.2µH, 2.8A Coilcraft ME3220-222
R2 10.0kΩ, 1% Vishay CRCW08051002F
R1 45.3kΩ, 1% Vishay CRCW08054532F
R3 100kΩ, 1% Vishay CRCW08051003F
Schottky 2A, 20V
f
R
Diodes Inc. B220/A
LM2832
www.national.com19
LM2832Y Design Example 4
LM2832
FIGURE 9. LM2832Y (550kHz): Vin = 5V, Vout = 3.3V@2.0A
Bill of Materials
Part ID Part Value Manufacturer Part Number
U1 1.5A Buck Regulator NSC LM2832Y
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.3V
L1 4.7µH 2.1A TDK SLF7045T-4R7M2R0-PF
R1 10.0kΩ, 1% Vishay CRCW08051002F
R2 10.0kΩ, 1% Vishay CRCW08051002F
Schottky 1.5A, 30V
f
20197508
R
TOSHIBA CRS08
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 Manufacturer Part Number
U1 1.5A Buck Regulator NSC LM2832Y
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.3V
L1 6.8µH 1.8A TDK SLF7045T-6R8M1R7
R1 10.0kΩ, 1% Vishay CRCW08051002F
R2 10.0kΩ, 1% Vishay CRCW08051002F
Schottky 1.5A, 30V
f
R
TOSHIBA CRS08
LM2832
www.national.com21
LM2832Z Design Example 6
LM2832
Part ID Part Value Manufacturer Part Number
U1 2.0A Buck Regulator NSC LM2832Z
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.4V
L1 3.3µH, 3.3A Coilcraft DS3316P-332
R2 10.0kΩ, 1% Vishay CRCW08051002F
R1 45.3kΩ, 1% Vishay CRCW08054532F
R3 100kΩ, 1% Vishay CRCW08051003F
FIGURE 11. LM2832Z (3MHz): Vin = 5V, Vo = 3.3V@2.0A
Bill of Materials
Schottky 2A, 20V
f
R
Diodes Inc. B220/A
20197508
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 Manufacturer Part Number
U1 2.0A Buck Regulator NSC LM2832Z
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
D1, Catch Diode 0.4V
L1 4.7µH, 2.7A Coilcraft DS3316P-472
R2 10.0kΩ, 1% Vishay CRCW08051002F
R1 10.0kΩ, 1% Vishay CRCW08051002F
R3 100kΩ, 1% Vishay CRCW08051003F
Schottky 2A, 20V
f
R
Diodes Inc. B220/A
LM2832
www.national.com23
LM2832X Dual Converters with Delayed Enabled Design Example 8
LM2832
20197562
FIGURE 13. LM2832X (1.6MHz): Vin = 5V, Vo = 1.2V@2.0A & 3.3V@2.0A
Bill of Materials
Part ID Part Value Manufacturer Part Number
U1, U2 2.0A Buck Regulator NSC LM2832X
U3 Power on Reset NSC LP3470M5X-3.08
C1, C3 Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, C4 Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
C7 Trr delay capacitor TDK
D1, D2 Catch Diode 0.4V
Schottky 2A, 20V
f
R
Diodes Inc. B220/A
L1, L2 3.3µH, 2.7A Coilcraft ME3220-102
R2, R4, R5 10.0kΩ, 1% Vishay CRCW08051002F
R1, R6 45.3kΩ, 1% Vishay CRCW08054532F
R3 100kΩ, 1% Vishay CRCW08051003F
www.national.com 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 Manufacturer Part Number
U1 2.0A Buck Regulator NSC LM2832X
U2 200mA LDO NSC LP2986-5.0
C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M
C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M
C3 – C6 2.2µF, 6.3V, X5R TDK C1608X5R0J225M
D1, Catch Diode 0.4V
D2 0.4V
L2 10µH, 800mA CoilCraft ME3220-103
L1 2.2µH, 3.5A CoilCraft DS3316P-222
R2 45.3kΩ, 1% Vishay CRCW08054532F
R1 10.0kΩ, 1% Vishay CRCW08051002F
Schottky 2A, 20V
f
Schottky 20VR, 500mA ON Semi MBR0520
f
R
Diodes Inc. B220/A
LM2832
www.national.com25
Physical Dimensions inches (millimeters) unless otherwise noted
LM2832
8-Lead eMSOP Package
NS Package Number MUY08A
6-Lead LLP Package
NS Package Number SDE06A
www.national.com 26
Notes
LM2832 High Frequency 2.0A Load - Step-Down DC-DC Regulator
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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