LM2736
Thin SOT23 750mA Load Step-Down DC-DC Regulator
General Description
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.
With a minimum of external components and online design
support through WEBENCH
TM
, the LM2736 is easy to use.
The ability to drive 750mA loads with an internal 350m
NMOS switch using state-of-the-art 0.5m 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.
Features
n
Thin SOT23-6 package
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
n
350m
NMOS switch
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"
V
IN
= 5V, V
OUT
= 3.3V
20124201
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WEBENCH
TM
is a trademark of Transim.
October 2004
LM2736
Thin
SOT23
750mA
Load
Step-Down
DC-DC
Regulator
2004 National Semiconductor Corporation
DS201242
www.national.com
Connection Diagram
20124205
6-Lead TSOT
NS Package Number MK06A
Ordering Information
Order Number
Package Type
NSC Package Drawing
Package Marking
Supplied As
LM2736XMK
TSOT-6
MK06A
SHAB
1000 Units on Tape and Reel
LM2736YMK
SHBB
1000 Units on Tape and Reel
LM2736XMKX
SHAB
3000 Units on Tape and Reel
LM2736YMKX
SHBB
3000 Units on Tape and Reel
* 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
FB
Feedback pin. Connect FB to the external resistor divider to set
output voltage.
4
EN
Enable control input. Logic high enables operation. Do not allow
this pin to float or be greater than V
IN
+ 0.3V.
5
V
IN
Input supply voltage. Connect a bypass capacitor to this pin.
6
SW
Output switch. Connects to the inductor, catch diode, and
bootstrap capacitor.
LM2736
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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.
V
IN
-0.5V to 22V
SW Voltage
-0.5V to 22V
Boost Voltage
-0.5V to 28V
Boost to SW Voltage
-0.5V to 6.0V
FB Voltage
-0.5V to 3.0V
EN Voltage
-0.5V to (V
IN
+ 0.3V)
Junction Temperature
150C
ESD Susceptibility (Note 2)
2kV
Storage Temp. Range
-65C to 150C
Soldering Information
Infrared/Convection Reflow (15sec)
220C
Wave Soldering Lead Temp. (10sec)
260C
Operating Ratings
(Note 1)
V
IN
3V to 18V
SW Voltage
-0.5V to 18V
Boost Voltage
-0.5V to 23V
Boost to SW Voltage
1.6V to 5.5V
Junction Temperature Range
-40C to +125C
Thermal Resistance
JA
(Note 3)
118C/W
Electrical Characteristics
Specifications with standard typeface are for T
J
= 25C, and those in boldface type apply over the full Operating Tempera-
ture Range (T
J
= -40C to 125C). V
IN
= 5V, V
BOOST
- V
SW
= 5V unless otherwise specified. Datasheet min/max specification
limits are guaranteed by design, test, or statistical analysis.
Symbol
Parameter
Conditions
Min
(Note 4)
Typ
(Note 5)
Max
(Note 4)
Units
V
FB
Feedback Voltage
1.225
1.250
1.275
V
V
FB
/
V
IN
Feedback Voltage Line
Regulation
V
IN
= 3V to 18V
0.01
% / V
I
FB
Feedback Input Bias Current
Sink/Source
10
250
nA
UVLO
Undervoltage Lockout
V
IN
Rising
2.74
2.90
V
Undervoltage Lockout
V
IN
Falling
2.0
2.3
UVLO Hysteresis
0.30
0.44
0.62
F
SW
Switching Frequency
LM2736X
1.2
1.6
1.9
MHz
LM2736Y
0.40
0.55
0.66
D
MAX
Maximum Duty Cycle
LM2736X
85
92
%
LM2736Y
90
96
D
MIN
Minimum Duty Cycle
LM2736X
2
%
LM2736Y
1
R
DS(ON)
Switch ON Resistance
V
BOOST
- V
SW
= 3V
350
650
m
I
CL
Switch Current Limit
V
BOOST
- V
SW
= 3V
1.0
1.5
2.3
A
I
Q
Quiescent Current
Switching
1.5
2.5
mA
Quiescent Current (shutdown)
V
EN
= 0V
30
nA
I
BOOST
Boost Pin Current
LM2736X (50% Duty Cycle)
2.2
3.3
mA
LM2736Y (50% Duty Cycle)
0.9
1.6
V
EN_TH
Shutdown Threshold Voltage
V
EN
Falling
0.4
V
Enable Threshold Voltage
V
EN
Rising
1.8
I
EN
Enable Pin Current
Sink/Source
10
nA
I
SW
Switch Leakage
40
nA
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, 1.5k
in series with 100pF.
Note 3: Thermal shutdown will occur if the junction temperature exceeds 165C. The maximum power dissipation is a function of T
J(MAX)
,
JA
and T
A
. The
maximum allowable power dissipation at any ambient temperature is P
D
= (T
J(MAX)
T
A
)/
JA
. All numbers apply for packages soldered directly onto a 3" x 3" PC
board with 2oz. copper on 4 layers in still air. For a 2 layer board using 1 oz. copper in still air,
JA
= 204C/W.
Note 4: Guaranteed to National's Average Outgoing Quality Level (AOQL).
Note 5: Typicals represent the most likely parametric norm.
LM2736
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3
Typical Performance Characteristics
All curves taken at V
IN
= 5V, V
BOOST
- V
SW
= 5V, L1 = 4.7 H
("X"), L1 = 10 H ("Y"), and T
A
= 25C, unless specified otherwise.
Efficiency vs Load Current - "X" V
OUT
= 5V
Efficiency vs Load Current - "Y" V
OUT
= 5V
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Efficiency vs Load Current - "X" V
OUT
= 3.3V
Efficiency vs Load Current - "Y" V
OUT
= 3.3V
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Efficiency vs Load Current - "X" V
OUT
= 1.5V
Efficiency vs Load Current - "Y" V
OUT
= 1.5V
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LM2736
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4
Typical Performance Characteristics
All curves taken at V
IN
= 5V, V
BOOST
- V
SW
= 5V, L1 = 4.7 H
("X"), L1 = 10 H ("Y"), and T
A
= 25C, unless specified otherwise. (Continued)
Oscillator Frequency vs Temperature - "X"
Oscillator Frequency vs Temperature - "Y"
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Current Limit vs Temperature
V
IN
= 18V, V
IN
= 5V
V
FB
vs Temperature
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R
DSON
vs Temperature
I
Q
Switching vs Temperature
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LM2736
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5
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