LM2736XMK [NSC]
Thin SOT23 750mA Load Step-Down DC-DC Regulator; 薄型SOT23 750毫安负载降压型DC -DC稳压器
| 型号： | LM2736XMK |
| 厂家： | 
National Semiconductor |
| 描述： | Thin SOT23 750mA Load Step-Down DC-DC Regulator |
| 文件： | 总22页 (文件大小：440K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
October 2004
LM2736
Thin SOT23 750mA Load Step-Down DC-DC Regulator
General Description
Features
n Thin SOT23-6 package
The LM2736 regulator is a monolithic, high frequency, PWM
step-down DC/DC converter in a 6-pin Thin SOT23 package.
It provides all the active functions to provide local DC/DC
conversion with fast transient response and accurate regu-
lation in the smallest possible PCB area.
n 3.0V to 18V input voltage range
n 1.25V to 16V output voltage range
n 750mA output current
n 550kHz (LM2736Y) and 1.6MHz (LM2736X)
switching frequencies
With a minimum of external components and online design
™
support through WEBENCH , the LM2736 is easy to use.
n 350mΩ NMOS switch
The ability to drive 750mA loads with an internal 350mΩ
NMOS switch using state-of-the-art 0.5µm BiCMOS technol-
ogy results in the best power density available. The world
class control circuitry allows for on-times as low as 13ns,
thus supporting exceptionally high frequency conversion
over the entire 3V to 18V input operating range down to the
minimum output voltage of 1.25V. Switching frequency is
internally set to 550kHz (LM2736Y) or 1.6MHz (LM2736X),
allowing the use of extremely small surface mount inductors
and chip capacitors. Even though the operating frequencies
are very high, efficiencies up to 90% are easy to achieve.
External shutdown is included, featuring an ultra-low
stand-by current of 30nA. The LM2736 utilizes current-mode
control and internal compensation to provide high-
performance regulation over a wide range of operating con-
ditions. Additional features include internal soft-start circuitry
to reduce inrush current, pulse-by-pulse current limit, ther-
mal shutdown, and output over-voltage protection.
n 30nA shutdown current
n 1.25V, 2% internal voltage reference
n Internal soft-start
n Current-Mode, PWM operation
n WEBENCH online design tool
Applications
n Local Point of Load Regulation
n Core Power in HDDs
n Set-Top Boxes
n Battery Powered Devices
n USB Powered Devices
n DSL Modems
n Notebook Computers
Typical Application Circuit
Efficiency vs Load Current "X"
VIN = 5V, VOUT = 3.3V
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™
WEBENCH is a trademark of Transim.
© 2004 National Semiconductor Corporation
DS201242
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Connection Diagram
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6-Lead TSOT
NS Package Number MK06A
Ordering Information
Order Number
LM2736XMK
Package Type NSC Package Drawing
Package Marking
Supplied As
SHAB
SHBB
SHAB
SHBB
1000 Units on Tape and Reel
1000 Units on Tape and Reel
3000 Units on Tape and Reel
3000 Units on Tape and Reel
LM2736YMK
TSOT-6
MK06A
LM2736XMKX
LM2736YMKX
* Contact the local sales office for the lead-free package.
Pin Description
Pin
Name
Function
1
BOOST
Boost voltage that drives the internal NMOS control switch. A
bootstrap capacitor is connected between the BOOST and SW
pins.
2
GND
Signal and Power ground pin. Place the bottom resistor of the
feedback network as close as possible to this pin for accurate
regulation.
3
4
FB
EN
Feedback pin. Connect FB to the 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.
Input supply voltage. Connect a bypass capacitor to this pin.
Output switch. Connects to the inductor, catch diode, and
bootstrap capacitor.
5
6
VIN
SW
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2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Soldering Information
Infrared/Convection Reflow (15sec)
Wave Soldering Lead Temp. (10sec)
220˚C
260˚C
VIN
-0.5V to 22V
-0.5V to 22V
-0.5V to 28V
-0.5V to 6.0V
-0.5V to 3.0V
-0.5V to (VIN + 0.3V)
150˚C
Operating Ratings (Note 1)
VIN
SW Voltage
3V to 18V
-0.5V to 18V
-0.5V to 23V
1.6V to 5.5V
−40˚C to +125˚C
118˚C/W
Boost Voltage
SW Voltage
Boost to SW Voltage
FB Voltage
Boost Voltage
Boost to SW Voltage
Junction Temperature Range
Thermal Resistance θJA (Note 3)
EN Voltage
Junction Temperature
ESD Susceptibility (Note 2)
Storage Temp. Range
2kV
-65˚C to 150˚C
Electrical Characteristics
Specifications with standard typeface are for TJ = 25˚C, and those in boldface type apply over the full Operating Tempera-
ture Range (TJ = -40˚C to 125˚C). VIN = 5V, VBOOST - VSW = 5V unless otherwise specified. Datasheet min/max specification
limits are guaranteed by design, test, or statistical analysis.
Min
(Note 4)
1.225
Typ
(Note 5)
1.250
Max
(Note 4)
1.275
Symbol
VFB
Parameter
Feedback Voltage
Conditions
Units
V
Feedback Voltage Line
Regulation
VIN = 3V to 18V
∆VFB/∆VIN
IFB
0.01
% / V
nA
Feedback Input Bias Current
Undervoltage Lockout
Undervoltage Lockout
UVLO Hysteresis
Sink/Source
VIN Rising
VIN Falling
10
2.74
2.3
0.44
1.6
0.55
92
250
2.90
UVLO
2.0
0.30
1.2
0.40
85
V
0.62
1.9
LM2736X
FSW
DMAX
DMIN
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
MHz
%
LM2736Y
0.66
LM2736X
LM2736Y
90
96
LM2736X
2
%
LM2736Y
1
RDS(ON)
ICL
Switch ON Resistance
Switch Current Limit
VBOOST - VSW = 3V
VBOOST - VSW = 3V
Switching
350
1.5
1.5
30
650
2.3
2.5
mΩ
A
1.0
1.8
IQ
Quiescent Current
mA
nA
Quiescent Current (shutdown)
VEN = 0V
LM2736X (50% Duty Cycle)
LM2736Y (50% Duty Cycle)
VEN Falling
2.2
0.9
3.3
1.6
0.4
IBOOST
VEN_TH
Boost Pin Current
mA
V
Shutdown Threshold Voltage
Enable Threshold Voltage
Enable Pin Current
VEN Rising
IEN
Sink/Source
10
40
nA
nA
ISW
Switch Leakage
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see Electrical Characteristics.
Note 2: Human body model, 1.5kΩ in series with 100pF.
Note 3: Thermal shutdown will occur if the junction temperature exceeds 165˚C. The maximum power dissipation is a function of T
, θ and T . The
JA A
J(MAX)
maximum allowable power dissipation at any ambient temperature is P = (T
– T )/θ . All numbers apply for packages soldered directly onto a 3” x 3” PC
D
J(MAX)
A JA
board with 2oz. copper on 4 layers in still air. For a 2 layer board using 1 oz. copper in still air, θ = 204˚C/W.
JA
Note 4: Guaranteed to National’s Average Outgoing Quality Level (AOQL).
Note 5: Typicals represent the most likely parametric norm.
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Typical Performance Characteristics All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH
("X"), L1 = 10 µH ("Y"), and TA = 25˚C, unless specified otherwise.
Efficiency vs Load Current - "X" VOUT = 5V
Efficiency vs Load Current - "Y" VOUT = 5V
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Efficiency vs Load Current - "X" VOUT = 3.3V
Efficiency vs Load Current - "Y" VOUT = 3.3V
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Efficiency vs Load Current - "X" VOUT = 1.5V
Efficiency vs Load Current - "Y" VOUT = 1.5V
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Typical Performance Characteristics All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH
("X"), L1 = 10 µH ("Y"), and TA = 25˚C, unless specified otherwise. (Continued)
Oscillator Frequency vs Temperature - "X"
Oscillator Frequency vs Temperature - "Y"
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Current Limit vs Temperature
VIN = 18V, VIN = 5V
VFB vs Temperature
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RDSON vs Temperature
IQ Switching vs Temperature
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Typical Performance Characteristics All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH
("X"), L1 = 10 µH ("Y"), and TA = 25˚C, unless specified otherwise. (Continued)
Line Regulation - "X"
Line Regulation - "Y"
VOUT = 1.5V, IOUT = 500mA
VOUT = 1.5V, IOUT = 500mA
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Line Regulation - "X"
Line Regulation - "Y"
VOUT = 3.3V, IOUT = 500mA
VOUT = 3.3V, IOUT = 500mA
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Block Diagram
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FIGURE 1.
forward voltage (VD) of the catch diode. The regulator loop
adjusts the duty cycle (D) to maintain a constant output
voltage.
Application Information
THEORY OF OPERATION
The LM2736 is a constant frequency PWM buck regulator IC
that delivers a 750mA load current. The regulator has a
preset switching frequency of either 550kHz (LM2736Y) or
1.6MHz (LM2736X). These high frequencies allow the
LM2736 to operate with small surface mount capacitors and
inductors, resulting in DC/DC converters that require a mini-
mum amount of board space. The LM2736 is internally
compensated, so it is simple to use, and requires few exter-
nal components. The LM2736 uses current-mode control to
regulate the output voltage.
The following operating description of the LM2736 will refer
to the Simplified Block Diagram (Figure 1) and to the wave-
forms in Figure 2. The LM2736 supplies a regulated output
voltage by switching the internal NMOS 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 NMOS control
switch. During this on-time, the SW pin voltage (VSW) swings
up to approximately VIN, and the inductor current (IL) in-
creases 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 am-
plifier’s output, which is proportional to the difference be-
tween 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 Schottky diode D1,
which forces the SW pin to swing below ground by the
20124207
FIGURE 2. LM2736 Waveforms of SW Pin Voltage and
Inductor Current
BOOST FUNCTION
Capacitor CBOOST and diode D2 in Figure 3 are used to
generate a voltage VBOOST. VBOOST - VSW is the gate drive
voltage to the internal NMOS control switch. To properly
drive the internal NMOS switch during its on-time, VBOOST
needs to be at least 1.6V greater than VSW. Although the
LM2736 will operate with this minimum voltage, it may not
have sufficient gate drive to supply large values of output
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shown in Figure 4. When using a series zener diode from the
input, ensure that the regulation of the input supply doesn’t
create a voltage that falls outside the recommended VBOOST
voltage.
Application Information (Continued)
current. Therefore, it is recommended that VBOOST be
greater than 2.5V above VSW for best efficiency. VBOOST
–
VSW should not exceed the maximum operating limit of 5.5V.
<
>
)
(VINMAX – VD3
)
5.5V
1.6V
>
>
5.5V VBOOST – VSW 2.5V for best performance.
(VINMIN – VD3
20124208
20124209
FIGURE 3. VOUT Charges CBOOST
FIGURE 4. Zener Reduces Boost Voltage from VIN
When the LM2736 starts up, internal circuitry from the
BOOST pin supplies a maximum of 20mA to CBOOST. This
current charges CBOOST to a voltage sufficient to turn the
switch on. The BOOST pin will continue to source current to
CBOOST until the voltage at the feedback pin is greater than
1.18V.
An alternative method is to place the zener diode D3 in a
shunt configuration as shown in Figure 5. A small 350mW to
500mW 5.1V zener in a SOT-23 or SOD package can be
used for this purpose. A small ceramic capacitor such as a
6.3V, 0.1µF capacitor (C4) should be placed in parallel with
the zener diode. When the internal NMOS switch turns on, a
pulse of current is drawn to charge the internal NMOS gate
capacitance. The 0.1 µF parallel shunt capacitor ensures
that the VBOOST voltage is maintained during this time.
There are various methods to derive VBOOST
1. From the input voltage (VIN
2. From the output voltage (VOUT
:
)
)
Resistor R3 should be chosen to provide enough RMS cur-
rent to the zener diode (D3) and to the BOOST pin. A
recommended choice for the zener current (IZENER) is 1 mA.
The current IBOOST into the BOOST pin supplies the gate
current of the NMOS control switch and varies typically
according to the following formula:
3. From an external distributed voltage rail (VEXT
)
4. From a shunt or series zener diode
In the Simplifed Block Diagram of Figure 1, capacitor
CBOOST and diode D2 supply the gate-drive current for the
NMOS switch. Capacitor CBOOST is charged via diode D2 by
VIN. During a normal switching cycle, when the internal
NMOS control switch is off (TOFF) (refer to Figure 2), VBOOST
equals VIN minus the forward voltage of D2 (VFD2), during
which the current in the inductor (L) forward biases the
Schottky diode D1 (VFD1). Therefore the voltage stored
across CBOOST is
IBOOST = 0.56 x (D + 0.54) x (VZENER – VD2) mA
where D is the duty cycle, VZENER and VD2 are in volts, and
IBOOST is in milliamps. VZENER is the voltage applied to the
anode of the boost diode (D2), and VD2 is the average
forward voltage across D2. Note that this formula for IBOOST
gives typical current. For the worst case IBOOST, increase the
current by 40%. In that case, the worst case boost current
will be
VBOOST - VSW = VIN - VFD2 + VFD1
When the NMOS switch turns on (TON), the switch pin rises
to
IBOOST-MAX = 1.4 x IBOOST
R3 will then be given by
VSW = VIN – (RDSON x IL),
forcing VBOOST to rise thus reverse biasing D2. The voltage
at VBOOST is then
R3 = (VIN - VZENER) / (1.4 x IBOOST + IZENER
)
For example, let VIN = 10V, VZENER = 5V, VD2 = 0.7V, IZENER
= 1mA, and duty cycle D = 50%. Then
VBOOST = 2VIN – (RDSON x IL) – VFD2 + VFD1
which is approximately
IBOOST = 0.56 x (0.5 + 0.54) x (5 - 0.7) mA = 2.5mA
2VIN - 0.4V
R3 = (10V - 5V) / (1.4 x 2.5mA + 1mA) = 1.11kΩ
for many applications. Thus the gate-drive voltage of the
NMOS switch is approximately
VIN - 0.2V
An alternate method for charging CBOOST is to connect D2 to
the output as shown in Figure 3. The output voltage should
be between 2.5V and 5.5V, so that proper gate voltage will
be applied to the internal switch. In this circuit, CBOOST
provides a gate drive voltage that is slightly less than VOUT
.
In applications where both VIN and VOUT are greater than
5.5V, or less than 3V, CBOOST cannot be charged directly
from these voltages. If VIN and VOUT are greater than 5.5V,
CBOOST can be charged from VIN or VOUT minus a zener
voltage by placing a zener diode D3 in series with D2, as
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THERMAL SHUTDOWN
Application Information (Continued)
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.
Design Guide
INDUCTOR SELECTION
The Duty Cycle (D) can be approximated quickly using the
ratio of output voltage (VO) to input voltage (VIN):
20124248
The catch diode (D1) forward voltage drop and the voltage
drop across the internal NMOS must be included to calculate
a more accurate duty cycle. Calculate D by using the follow-
ing formula:
FIGURE 5. Boost Voltage Supplied from the Shunt
Zener on VIN
ENABLE PIN / SHUTDOWN MODE
The LM2736 has a shutdown mode that is controlled by the
enable pin (EN). When a logic low voltage is applied to EN,
the part is in shutdown mode and its quiescent current drops
to typically 30nA. Switch leakage adds another 40nA from
the input supply. The voltage at this pin should never exceed
VIN + 0.3V.
VSW can be approximated by:
VSW = IO x RDS(ON)
The diode forward drop (VD) can range from 0.3V to 0.7V
depending on the quality of the diode. The lower VD is, the
higher the operating efficiency of the converter.
SOFT-START
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 1.25V in
approximately 200µs. This forces the regulator output to
ramp up in a more linear and controlled fashion, which helps
reduce inrush current.
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. The ratio of
ripple current (∆iL) to output current (IO) is optimized when it
is set between 0.3 and 0.4 at 750mA. The ratio r is defined
as:
OUTPUT OVERVOLTAGE PROTECTION
The overvoltage comparator compares the FB pin voltage to
a voltage that is 10% higher than the internal reference Vref.
Once the FB pin voltage goes 10% above the internal refer-
ence, the internal NMOS control switch is turned off, which
allows the output voltage to decrease toward regulation.
One must also ensure that the minimum current limit (1.0A)
is not exceeded, so the peak current in the inductor must be
calculated. The peak current (ILPK) in the inductor is calcu-
lated by:
UNDERVOLTAGE LOCKOUT
Undervoltage lockout (UVLO) prevents the LM2736 from
operating until the input voltage exceeds 2.74V(typ).
ILPK = IO + ∆IL/2
The UVLO threshold has approximately 440mV of hyster-
esis, so the part will operate until VIN drops below 2.3V(typ).
Hysteresis prevents the part from turning off during power up
if VIN is non-monotonic.
If r = 0.7 at an output of 750mA, the peak current in the
inductor will be 1.0125A. The minimum guaranteed current
limit over all operating conditions is 1.0A. One can either
reduce r to 0.6 resulting in a 975mA peak current, or make
the engineering judgement that 12.5mA over will be safe
enough with a 1.5A typical current limit and 6 sigma limits.
When the designed maximum output current is reduced, the
ratio r can be increased. At a current of 0.1A, r can be made
as high as 0.9. The ripple ratio can be increased at lighter
loads because the net ripple is actually quite low, and if r
remains constant the inductor value can be made quite
large. An equation empirically developed for the maximum
ripple ratio at any current below 2A is:
CURRENT LIMIT
The LM2736 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 1.5A
(typ), and turns off the switch until the next switching cycle
begins.
-0.3667
r = 0.387 x IOUT
Note that this is just a guideline.
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pacitors and have very low ESL. For MLCCs it is recom-
mended to use X7R or X5R dielectrics. Consult capacitor
manufacturer datasheet to see how rated capacitance varies
over operating conditions.
Design Guide (Continued)
The LM2736 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
capacitor section for more details on calculating output volt-
age ripple.
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:
Now that the ripple current or ripple ratio is determined, the
inductance is calculated by:
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 LM2736, 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 at 10 µF of output capaci-
tance. Capacitance can be increased significantly with little
detriment to the regulator stability. Like the input capacitor,
recommended multilayer ceramic capacitors are X7R or
X5R. Again, verify actual capacitance at the desired operat-
ing voltage and temperature.
where fs is the switching frequency and IO is the output
current. When selecting an inductor, make sure that it is
capable of supporting the peak output current without satu-
rating. Inductor saturation will result in a sudden reduction in
inductance and prevent the regulator from operating cor-
rectly. 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 de-
signed maximum output current is 0.5A and the peak current
is 0.7A, then the inductor should be specified with a satura-
>
tion current limit of 0.7A. There is no need to specify the
saturation or peak current of the inductor at the 1.5A typical
switch current limit. The difference in inductor size is a factor
of 5. Because of the operating frequency of the LM2736,
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 (DCR) will provide better operating efficiency. For
recommended inductors see Example Circuits.
Check the RMS current rating of the capacitor. The RMS
current rating of the capacitor chosen must also meet the
following condition:
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 10µF, al-
though 4.7µF works well for input voltages below 6V. 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:
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 = IO 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.
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 ce-
ramic chip capacitor will have very low ESL. At the operating
frequencies of the LM2736, certain 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.
Sanyo POSCAP, Tantalum or Niobium, Panasonic SP or
Cornell Dubilier ESR, and multilayer ceramic capacitors
(MLCC) are all good choices for both input and output ca-
BOOST DIODE
A standard diode such as the 1N4148 type is recommended.
For VBOOST circuits derived from voltages less than 3.3V, a
small-signal Schottky diode is recommended for greater ef-
ficiency. A good choice is the BAT54 small signal diode.
BOOST CAPACITOR
A ceramic 0.01µF capacitor with a voltage rating of at least
6.3V is sufficient. The X7R and X5R MLCCs provide the best
performance.
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GND connection of the COUT capacitor, which should be
near the GND connections of CIN and D1.
Design Guide (Continued)
OUTPUT VOLTAGE
There should be a continuous ground plane on the bottom
layer of a two-layer board except under the switching node
island.
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.
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 R2
placed as close as possible to the GND of the IC. The VOUT
trace to R1 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.
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 when completing the layout is the
close coupling of the GND connections of the CIN 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
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 LM2736 demo board as an
example of a four-layer layout.
11
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LM2736X Circuit Examples
20124242
FIGURE 6. LM2736X (1.6MHz)
VBOOST Derived from VIN
5V to 1.5V/750mA
Bill of Materials for Figure 6
Part ID
Part Value
Part Number
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 6.3V, X5R
LM2736X
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
L1
C3216X5ROJ106M
C3216X5ROJ106M
C1005X7R1C103K
MBRM110L
10µF, 6.3V, X5R
TDK
0.01uF, 16V, X7R
TDK
0.3VF Schottky 1A, 10VR
ON Semi
Diodes, Inc.
TDK
@
1VF 50mA Diode
1N4148W
4.7µH, 1.7A,
2kΩ, 1%
VLCF4020T- 4R7N1R2
CRCW06032001F
CRCW06031002F
CRCW06031003F
R1
Vishay
R2
10kΩ, 1%
100kΩ, 1%
Vishay
R3
Vishay
www.national.com
12
LM2736X Circuit Examples (Continued)
20124243
FIGURE 7. LM2736X (1.6MHz)
VBOOST Derived from VOUT
12V to 3.3V/750mA
Bill of Materials for Figure 7
Part ID
Part Value
Part Number
Manufacturer
U1
750mA Buck Regulator
10µF, 25V, X7R
LM2736X
National Semiconductor
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
L1
C3225X7R1E106M
C3216X5ROJ226M
C1005X7R1C103K
SS1P3L
TDK
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.34VF Schottky 1A, 30VR
Vishay
Vishay
TDK
@
0.6VF 30mA Diode
BAT17
4.7µH, 1.7A,
16.5kΩ, 1%
10.0 kΩ, 1%
100kΩ, 1%
VLCF4020T- 4R7N1R2
CRCW06031652F
CRCW06031002F
CRCW06031003F
R1
Vishay
Vishay
Vishay
R2
R3
13
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LM2736X Circuit Examples (Continued)
20124244
FIGURE 8. LM2736X (1.6MHz)
VBOOST Derived from VSHUNT
18V to 1.5V/750mA
Bill of Materials for Figure 8
Part ID
Part Value
Part Number
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 25V, X7R
LM2736X
C1, Input Cap
C2, Output Cap
C3, Boost Cap
C4, Shunt Cap
D1, Catch Diode
D2, Boost Diode
D3, Zener Diode
L1
C3225X7R1E106M
C3216X5ROJ226M
C1005X7R1C103K
C1005X5R0J104K
SS1P3L
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
0.1µF, 6.3V, X5R
TDK
TDK
0.4VF Schottky 1A, 30VR
Vishay
@
1VF 50mA Diode
1N4148W
Diodes, Inc.
Vishay
5.1V 250Mw SOT-23
6.8µH, 1.6A,
2kΩ, 1%
BZX84C5V1
SLF7032T-6R8M1R6
CRCW06032001F
CRCW06031002F
CRCW06031003F
CRCW06034121F
TDK
R1
Vishay
R2
10kΩ, 1%
Vishay
R3
100kΩ, 1%
Vishay
R4
4.12kΩ, 1%
Vishay
www.national.com
14
LM2736X Circuit Examples (Continued)
20124249
FIGURE 9. LM2736X (1.6MHz)
VBOOST Derived from Series Zener Diode (VIN
15V to 1.5V/750mA
)
Bill of Materials for Figure 9
Part ID
Part Value
Part Number
LM2736X
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 25V, X7R
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
D3, Zener Diode
L1
C3225X7R1E106M
C3216X5ROJ226M
C1005X7R1C103K
SS1P3L
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.4VF Schottky 1A, 30VR
Vishay
@
1VF 50mA Diode
1N4148W
Diodes, Inc.
Diodes, Inc.
TDK
11V 350Mw SOT-23
6.8µH, 1.6A,
2kΩ, 1%
BZX84C11T
SLF7032T-6R8M1R6
CRCW06032001F
CRCW06031002F
CRCW06031003F
R1
Vishay
R2
10kΩ, 1%
Vishay
R3
100kΩ, 1%
Vishay
15
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LM2736X Circuit Examples (Continued)
20124250
FIGURE 10. LM2736X (1.6MHz)
VBOOST Derived from Series Zener Diode (VOUT
)
15V to 9V/750mA
Bill of Materials for Figure 10
Part ID
Part Value
Part Number
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 25V, X7R
LM2736X
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
D3, Zener Diode
L1
C3225X7R1E106M
C3216X5R1C226M
C1005X7R1C103K
SS1P3L
22µF, 16V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.4VF Schottky 1A, 30VR
Vishay
@
1VF 50mA Diode
1N4148W
Diodes, Inc.
Diodes, Inc.
TDK
4.3V 350mw SOT-23
6.8µH, 1.6A,
61.9kΩ, 1%
BZX84C4V3
SLF7032T-6R8M1R6
CRCW06036192F
CRCW06031002F
CRCW06031003F
R1
Vishay
R2
10kΩ, 1%
Vishay
R3
100kΩ, 1%
Vishay
www.national.com
16
LM2736Y Circuit Examples
20124242
FIGURE 11. LM2736Y (550kHz)
VBOOST Derived from VIN
5V to 1.5V/750mA
Bill of Materials for Figure 11
Part ID
Part Value
Part Number
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 6.3V, X5R
LM2736Y
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
L1
C3216X5ROJ106M
C3216X5ROJ226M
C1005X7R1C103K
MBRM110L
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.3VF Schottky 1A, 10VR
ON Semi
Diodes, Inc.
TDK
@
1VF 50mA Diode
1N4148W
10µH, 1.6A,
2kΩ, 1%
SLF7032T-100M1R4
CRCW06032001F
CRCW06031002F
CRCW06031003F
R1
Vishay
R2
10kΩ, 1%
100kΩ, 1%
Vishay
R3
Vishay
17
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LM2736Y Circuit Examples (Continued)
20124243
FIGURE 12. LM2736Y (550kHz)
VBOOST Derived from VOUT
12V to 3.3V/750mA
Bill of Materials for Figure 12
Part ID
Part Value
Part Number
Manufacturer
U1
750mA Buck Regulator
10µF, 25V, X7R
LM2736Y
National Semiconductor
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
L1
C3225X7R1E106M
C3216X5ROJ226M
C1005X7R1C103K
SS1P3L
TDK
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.34VF Schottky 1A, 30VR
Vishay
Vishay
TDK
@
0.6VF 30mA Diode
BAT17
10µH, 1.6A,
16.5kΩ, 1%
10.0 kΩ, 1%
100kΩ, 1%
SLF7032T-100M1R4
CRCW06031652F
CRCW06031002F
CRCW06031003F
R1
Vishay
Vishay
Vishay
R2
R3
www.national.com
18
LM2736Y Circuit Examples (Continued)
20124244
FIGURE 13. LM2736Y (550kHz)
VBOOST Derived from VSHUNT
18V to 1.5V/750mA
Bill of Materials for Figure 13
Part ID
Part Value
Part Number
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 25V, X7R
LM2736Y
C1, Input Cap
C2, Output Cap
C3, Boost Cap
C4, Shunt Cap
D1, Catch Diode
D2, Boost Diode
D3, Zener Diode
L1
C3225X7R1E106M
C3216X5ROJ226M
C1005X7R1C103K
C1005X5R0J104K
SS1P3L
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
0.1µF, 6.3V, X5R
TDK
TDK
0.4VF Schottky 1A, 30VR
Vishay
@
1VF 50mA Diode
1N4148W
Diodes, Inc.
Vishay
5.1V 250Mw SOT-23
15µH, 1.5A
2kΩ, 1%
BZX84C5V1
SLF7045T-150M1R5
CRCW06032001F
CRCW06031002F
CRCW06031003F
CRCW06034121F
TDK
R1
Vishay
R2
10kΩ, 1%
Vishay
R3
100kΩ, 1%
Vishay
R4
4.12kΩ, 1%
Vishay
19
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LM2736Y Circuit Examples (Continued)
20124249
FIGURE 14. LM2736Y (550kHz)
VBOOST Derived from Series Zener Diode (VIN
)
15V to 1.5V/750mA
Bill of Materials for Figure 14
Part ID
Part Value
Part Number
LM2736Y
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 25V, X7R
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
D3, Zener Diode
L1
C3225X7R1E106M
C3216X5ROJ226M
C1005X7R1C103K
SS1P3L
22µF, 6.3V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.4VF Schottky 1A, 30VR
Vishay
@
1VF 50mA Diode
1N4148W
Diodes, Inc.
Diodes, Inc.
TDK
11V 350Mw SOT-23
15µH, 1.5A,
2kΩ, 1%
BZX84C11T
SLF7045T-150M1R5
CRCW06032001F
CRCW06031002F
CRCW06031003F
R1
Vishay
R2
10kΩ, 1%
Vishay
R3
100kΩ, 1%
Vishay
www.national.com
20
LM2736Y Circuit Examples (Continued)
20124250
FIGURE 15. LM2736Y (550kHz)
VBOOST Derived from Series Zener Diode (VOUT
)
15V to 9V/750mA
Bill of Materials for Figure 15
Part ID
Part Value
Part Number
LM2736Y
Manufacturer
National Semiconductor
TDK
U1
750mA Buck Regulator
10µF, 25V, X7R
C1, Input Cap
C2, Output Cap
C3, Boost Cap
D1, Catch Diode
D2, Boost Diode
D3, Zener Diode
L1
C3225X7R1E106M
C3216X5R1C226M
C1005X7R1C103K
SS1P3L
22µF, 16V, X5R
TDK
0.01µF, 16V, X7R
TDK
0.4VF Schottky 1A, 30VR
Vishay
@
1VF 50mA Diode
1N4148W
Diodes, Inc.
Diodes, Inc.
TDK
4.3V 350mw SOT-23
22µH, 1.4A,
BZX84C4V3
SLF7045T-220M1R3-1PF
CRCW06036192F
R1
61.9kΩ, 1%
Vishay
R2
10kΩ, 1%
CRCW06031002F
Vishay
R3
100kΩ, 1%
CRCW06031003F
Vishay
21
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Physical Dimensions inches (millimeters) unless otherwise noted
6-Lead TSOT Package
NS Package Number MK06A
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