TI1 LMR14203XMKX Simple switcherâ® 42vin, 0.3a step-down voltage regulator in sot-23 Datasheet

LMR14203
LMR14203 SIMPLE SWITCHER ® 42Vin, 0.3A Step-Down Voltage Regulator in
SOT-23
Literature Number: SNVS732A
LMR14203
SIMPLE SWITCHER® 42Vin, 0.3A Step-Down Voltage
Regulator in SOT-23
Features
Applications
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Input voltage range of 4.5V to 42V
Output voltage range of 0.765V to 34V
Output current up to 0.3A
1.25 MHz switching frequency
Low shutdown Iq, 16 µA typical
Short circuit protected
Internally compensated
Soft-start function
Thin SOT23-6 package (2.97 x 1.65 x 1mm)
Fully enabled for WEBENCH® Power Designer
Point-of-Load Conversions from 5V, 12V, and 24V Rails
Space Constrained Applications
Battery Powered Equipment
Industrial Distributed Power Applications
Power Meters
Portable Hand-Held Instruments
Performance Benefits
■ Tight accuracy for powering digital ICs
■ Extremely easy to use
■ Tiny overall solution reduces system cost
System Performance
Efficiency vs Load Current
VIN = 24V, VOUT = 1.2V and 3.3V
100
100
90
90
80
80
70
70
EFFICIENCY (%)
EFFICIENCY (%)
Efficiency vs Load Current
VIN = 12V, VOUT = 1.2V and 3.3V
60
50
40
30
20
50
40
30
20
10
10
1.2Vout
3.3Vout
0
0.00
60
0.05 0.10 0.15 0.20 0.25
LOAD CURRENT (A)
1.2Vout
3.3Vout
0
0.30
0.00
0.05 0.10 0.15 0.20 0.25
LOAD CURRENT (A)
30167073
0.30
30167074
30167002
© 2011 Texas Instruments Incorporated
301670
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LMR14203 SIMPLE SWITCHER® 42Vin, 0.3A Step-Down Voltage Regulator in SOT-23
November 1, 2011
LMR14203
Connection Diagram
Top View
30167004
TSOT 6 Lead
NS Package Number MK06A
Ordering Information
Order Number
Spec.
Package Type
NSC
Package
Drawing
Top Mark
Supplied As
NOPB
TSOT-6
MK06A
SJ3B
1000 Units, Tape and Reel
LMR14203XMKE
250 Units, Tape and Reel
LMR14203XMK
LMR14203XMKX
3000 Units, Tape and Reel
Pin Descriptions
Pin
Name
1
CB
2
GND
3
FB
4
SHDN
Function
SW FET gate bias voltage. Connect CBOOT cap between CB and SW.
Ground connection.
Feedback pin: Set feedback voltage divider ratio with VOUT = VFB (1+(R1/R2)). Resistors should
be in the 100-10K range to avoid input bias errors.
Logic level shutdown input. Pull to GND to disable the device and pull high to enable the device.
If this function is not used tie to VIN or leave open.
5
VIN
Power input voltage pin: 4.5V to 42V normal operating range.
6
SW
Power FET output: Connect to inductor, diode, and CBOOT cap.
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2
If Military/Aerospace specified devices are required,
please contact the Texas Instruments Sales Office/
Distributors for availability and specifications.
VIN
SHDN
SW Voltage
CB Voltage above SW Voltage
FB Voltage
Maximum Junction
Temperature
Power Dissipation(Note 2)
-0.3V to +45V
-0.3V to (VIN+0.3V)
SHDN=VIN at 45V max
-0.3V to +45V
7V
-0.3V to +5V
150°C
Operating Conditions
Operating Junction
Temperature Range (Note 4)
Storage Temperature
Input Voltage VIN
SW Voltage
−40°C to +125°C
−65°C to +150°C
4.5V to 42V
Up to 42V
Internally Limited
Electrical Characteristics
Specifications in standard type face are for TJ = 25°C and those with boldface type apply over the full Operating Temperature
Range ( TJ = −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. Unless otherwise
stated the following conditions apply: VIN = 12V.
Symbol
IQ
Parameter
Quiescent current
Conditions
Min (Note 4) Typ (Note 5) Max (Note 4)
Units
µA
SHDN = 0V
16
40
Device On, Not Switching
1.30
1.75
Device On, No Load
1.35
1.85
mA
RDSON
Switch ON resistance
(Note 6)
0.9
1.6
Ω
ILSW
Switch leakage current
VIN = 42V
0.0
0.5
µA
ICL
Switch current limit
(Note 7)
525
IFB
Feedback pin bias current
(Note 8)
0.1
1.0
VFB
FB Pin reference voltage
0.765
0.782
tMIN
Minimum ON time
fSW
Switching frequency
0.747
100
VFB = 0.5V
0.95
VFB = 0V
DMAX
Maximum duty cycle
VUVP
Undervoltage lockout thresholds On threshold
Shutdown threshold
81
87
4.4
3.7
3.5
Device on
2.3
Device off
ISHDN
1.25
Shutdown pin input bias current VSHDN = 2.3V (Note 8)
VSHDN = 0V
µA
V
ns
1.50
0.35
Off threshold
VSHDN
mA
MHz
%
3.25
1.0
0.9
0.3
0.05
1.5
0.02
1.5
V
V
µA
THERMAL SPECIFICATIONS
RθJA
Junction-to-Ambient Thermal
Resistance, TSOT-6L Package
(Note 9)
121
3
°C/W
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LMR14203
For soldering specifications: see product folder at
www.national.com and www.national.com/ms/MS/MSSOLDERING.pdf
ESD Susceptibility
(Note 3)
Human Body Model
1.5 kV
Absolute Maximum Ratings (Note 1)
LMR14203
Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended
to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance,
θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using: PD (MAX) = (TJ(MAX) − TA)/
θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal
shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=175°C (typ.) and disengages at TJ=155°C (typ).
Note 3: Human Body Model, applicable std. JESD22-A114-C.
Note 4: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Note 5: Typical numbers are at 25°C and represent the most likely norm.
Note 6: Includes the bond wires, RDSON from VIN pin to SW pin.
Note 7: Current limit at 0% duty cycle.
Note 8: Bias currents flow into pin.
Note 9: All numbers apply for packages soldered directly onto a 3" x 3" PC board with 2 oz. copper on 4 layers in still air in accordance to JEDEC standards.
Thermal resistance varies greatly with layout, copper thickness, number of layers in PCB, power distribution, number of thermal vias, board size, ambient
temperature, and air flow.
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4
LMR14203
Typical Performance Characteristics
Efficiency vs. Load Current
(VOUT = 3.3V)
Input UVLO Voltage vs. Temperature
30167067
30167018
Switch Current Limit vs. SHDN Pin Voltage
(Soft-start Implementation)
SHDN Pin Current vs. SHDN Pin Voltage
30167069
30167068
Load Transient Waveforms
Switching Node and Output Voltage Waveforms
30167070
VIN = 12V, VOUT = 3.3V, IOUT = 200 mA
Top trace: VOUT, 10 mV/div, AC Coupled
Bottom trace: SW, 5V/div, DC Coupled
T = 1 µs/div
30167071
VIN = 12V, VOUT = 3.3V, IOUT = 300 mA to 200 mA to 300 mA
Top trace: VOUT, 20 mV/div, AC Coupled
Bottom trace: IOUT, 100 mA/div, DC Coupled
T = 200 µs/div
5
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LMR14203
Start-Up Waveform
30167072
VIN = 12V, VOUT = 3.3V, IOUT = 50 mA
Top trace: VOUT, 1V/div, DC Coupled
Bottom trace: SHDN, 2V/div, DC Coupled
T = 40 µs/div
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6
LMR14203
Block Diagram
30167003
ductor current never reaches zero at steady state), the buck
regulator operates in two cycles. The power switch is connected between VIN and SW. In the first cycle of operation the
transistor is closed and the diode is reverse biased. Energy
is collected in the inductor and the load current is supplied by
COUT and the rising current through the inductor. During the
second cycle the transistor is open and the diode is forward
biased due to the fact that the inductor current cannot instantaneously change direction. The energy stored in the inductor
is transferred to the load and output capacitor. The ratio of
these two cycles determines the output voltage. The output
voltage is defined approximately as: D=VOUT/VIN and D’ = (1D) where D is the duty cycle of the switch. D and D' will be
required for design calculations.
General Description
The LMR14203 is a PWM DC/DC buck (step-down) regulator.
With a wide input range from 4.5V-42V, it is suitable for a wide
range of applications such as power conditioning from unregulated sources. They feature a low RDSON (0.9Ω typical) internal switch for maximum efficiency (85% typical). Operating
frequency is fixed at 1.25 MHz allowing the use of small external components while still being able to have low output
voltage ripple. Soft-start can be implemented using the shutdown pin with an external RC circuit allowing the user to tailor
the soft-start time to a specific application.
The LMR14203 is optimized for up to 300 mA load current.
Additional features include: thermal shutdown, VIN under-voltage lockout, and gate drive under-voltage lockout. The
LMR14203 is available in a low profile TSOT-6L package.
DESIGN PROCEDURE
This section presents guidelines for selecting external components.
Application Information
SETTING THE OUTPUT VOLTAGE
The output voltage is set using the feedback pin and a resistor
divider connected to the output as shown on the front page
schematic. The feedback pin voltage is 0.762V, so the ratio
of the feedback resistors sets the output voltage according to
the following equation: VOUT=0.765V(1+(R1/R2)) Typically
R2 will be given as 100Ω-10 kΩ for a starting value. To solve
for R1 given R2 and VOUT use R1=R2((VOUT/0.765V)-1).
PROTECTION
The LMR14203 has dedicated protection circuitry running
during normal operation to protect the IC. The thermal shutdown circuitry turns off the power device when the die temperature reaches excessive levels. The UVLO comparator
protects the power device during supply power startup and
shutdown to prevent operation at voltages less than the minimum input voltage. A gate drive (CB) under-voltage lockout
is included to guarantee that there is enough gate drive voltage to drive the MOSFET before the device tries to start
switching. The LMR14203 also features a shutdown mode
decreasing the supply current to approximately 16 µA.
INPUT CAPACITOR
A low ESR ceramic capacitor (CIN) is needed between the
VIN pin and GND pin. This capacitor prevents large voltage
transients from appearing at the input. Use a 2.2 µF-10 µF
value with X5R or X7R dielectric. Depending on construction,
a ceramic capacitor’s value can decrease up to 50% of its
nominal value when rated voltage is applied. Consult with the
capacitor manufacturer's data sheet for information on capacitor derating over voltage and temperature.
CONTINUOUS CONDUCTION MODE
The LMR14203 contains a current-mode, PWM buck regulator. A buck regulator steps the input voltage down to a lower
output voltage. In continuous conduction mode (when the in-
7
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LMR14203
RC filter is used to tailor the soft-start for a specific application.
When a voltage applied to the SHDN pin is between 0V and
up to 2.3V it will cause the cycle by cycle current limit in the
power stage to be modulated for minimum current limit at 0V
up to the rated current limit at 2.3V. Thus controlling the output
rise time and inrush current at startup. The resistor value
should be selected so the current sourced into the SHDN pin
will be greater then the leakage current of the SHDN pin (1.5
µA ) when the voltage at SHDN is equal or greater then 2.3V.
INDUCTOR SELECTION
The most critical parameters for the inductor are the inductance, peak current, and the DC resistance. The inductance
is related to the peak-to-peak inductor ripple current, the input
and the output voltages.
SHUTDOWN OPERATION
The SHDN pin of the LMR14203 is designed so that it may
be controlled using 2.3V or higher logic signals. If the shutdown function is not to be used the SHDN pin may be tied to
VIN. The maximum voltage to the SHDN pin should not exceed 42V. If the use of a higher voltage is desired due to
system or other constraints it may be used, however a 100
kΩ or larger resistor is recommended between the applied
voltage and the SHDN pin to protect the device.
A higher value of ripple current reduces inductance, but increases the conductance loss, core loss, and current stress
for the inductor and switch devices. It also requires a bigger
output capacitor for the same output voltage ripple requirement. A reasonable value is setting the ripple current to be
30% of the DC output current. Since the ripple current increases with the input voltage, the maximum input voltage is
always used to determine the inductance. The DC resistance
of the inductor is a key parameter for the efficiency. Lower DC
resistance is available with a bigger winding area. A good
tradeoff between the efficiency and the core size is letting the
inductor copper loss equal 2% of the output power. See
AN-1197 for more information on selecting inductors. A good
starting point for most applications is a 10 µH to 22 µH with a
0.7A or greater current rating for the LMR14203. Using such
a rating will enable the LMR14203 to current limit without saturating the inductor. This is preferable to the device going into
thermal shutdown mode and the possibility of damaging the
inductor if the output is shorted to ground or other longterm
overload.
SCHOTTKY DIODE
The breakdown voltage rating of the diode (D1) is preferred
to be 25% higher than the maximum input voltage. The current rating for the diode should be equal to the maximum
output current for best reliability in most applications. In cases
where the input voltage is much greater than the output voltage the average diode current is lower. In this case it is
possible to use a diode with a lower average current rating,
approximately (1-D)IOUT, however the peak current rating
should be higher than the maximum load current. A 0.5A to
1A rated diode is a good starting point.
OUTPUT CAPACITOR
The selection of COUT is driven by the maximum allowable
output voltage ripple. The output ripple in the constant frequency, PWM mode is approximated by: VRIPPLE = IRIPPLE
(ESR+(1/(8fSWCOUT))) The ESR term usually plays the dominant role in determining the voltage ripple. Low ESR ceramic
capacitors are recommended. Capacitors in the range of 22
µF-100 µF are a good starting point with an ESR of 0.1Ω or
less.
LAYOUT CONSIDERATIONS
To reduce problems with conducted noise pick up, the ground
side of the feedback network should be connected directly to
the GND pin with its own connection. The feedback network,
resistors R1 and R2, should be kept close to the FB pin, and
away from the inductor to minimize coupling noise into the
feedback pin. The input bypass capacitor CIN must be placed
close to the VIN pin. This will reduce copper trace resistance
which effects input voltage ripple of the IC. The inductor L1
should be placed close to the SW pin to reduce magnetic and
electrostatic noise. The output capacitor, COUT should be
placed close to the junction of L1 and the diode D1. The L1,
D1, and COUT trace should be as short as possible to reduce
conducted and radiated noise and increase overall efficiency.
The ground connection for the diode, CIN, and COUT should
be as small as possible and tied to the system ground plane
in only one spot (preferably at the COUT ground point) to minimize conducted noise in the system ground plane. For more
detail on switching power supply layout considerations see
Application Note AN-1149: Layout Guidelines for Switching
Power Supplies.
BOOTSTRAP CAPACITOR
A 0.15 µF ceramic capacitor or larger is recommended for the
bootstrap capacitor (CBOOT). For applications where the input
voltage is less than twice the output voltage a larger capacitor
is recommended, generally 0.15 µF to 1 µF to ensure plenty
of gate drive for the internal switches and a consistently low
RDSON.
SOFT-START COMPONENTS
The LMR14203 has circuitry that is used in conjunction with
the SHDN pin to limit the inrush current on start-up of the DC/
DC switching regulator. The SHDN pin in conjunction with a
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8
LMR14203
Typical Applications
30167005
FIGURE 1. Application Circuit, 3.3V Output
30167008
FIGURE 2. Application Circuit, 5V Output
30167009
FIGURE 3. Application Circuit, 12V Output
9
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LMR14203
30167016
FIGURE 4. Application Circuit, 15V Output
30167017
FIGURE 5. Application Circuit, 0.8V Output
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10
LMR14203
Physical Dimensions inches (millimeters) unless otherwise noted
TSOT 6 Pin Package (MK)
For Ordering, Refer to Ordering Information Table
NS Package Number MK06A
11
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