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LM2734
User Manual
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Texas Instruments LM2734 User Manual

LM2734
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LM2734 Thin SOT 1A Load Step-Down DC-DC Regulator
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1
FEATURES
234
• Thin SOT-6 Package
• 3.0V to 20V Input Voltage Range
• 0.8V to 18V Output Voltage Range
• 1A Output Current
• 550kHz (LM2734Y) and 1.6MHz (LM2734X) Switching Frequencies
• 300mΩ NMOS Switch
• 30nA Shutdown Current
• 0.8V, 2% Internal Voltage Reference
• Internal Soft-Start
• Current-Mode, PWM Operation
• WEBENCH®Online Design Tool
• Thermal Shutdown
• LM2734XQ/LM2734YQ are AEC-Q100 Grade 1 Qualified and are Manufactured on an Automotive Grade Flow
APPLICATIONS
• Local Point of Load Regulation
• Core Power in HDDs
• Set-Top Boxes
• Battery Powered Devices
• USB Powered Devices
• DSL Modems
• Notebook Computers
• Automotive
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
DESCRIPTION
With a minimum of external components and online design support through WEBENCH®, the LM2734 is easy to use. The ability to drive 1A loads with an internal 300mΩ NMOS switch using state-of-the-art
0.5µm BiCMOS technology 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 20V input operating range down to the minimum output voltage of 0.8V. Switching frequency is internally set to 550kHz (LM2734Y) or 1.6MHz (LM2734X), 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 LM2734 utilizes current-mode control and internal compensation to provide high­performance 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.
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2WEBENCH is a registered trademark of Texas Instruments, Inc.. 3WEBENCH is a registered trademark of Texas Instruments. 4All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright © 2004–2013, Texas Instruments Incorporated
1
2
3
6
5
4
BOOST
GND
FB
SW
V
IN
EN
1
2
3
6
5
4
LM2734
VIN
VIN
EN
BOOST
SW
FB
GND
V
OUT
C3
L1
C1
C2
R1
R2
D1
D2
ON
OFF
LM2734
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
Typical Application Circuit
Figure 1. Figure 2. Efficiency vs Load Current
Connection Diagram
VIN= 5V, V
OUT
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= 3.3V
Figure 3. 6-Lead SOT Figure 4. Pin 1 Indentification
See Package Number DDC (R-PDSO-G6)
Pin Name Function
1 BOOST Boost voltage that drives the internal NMOS control switch. A bootstrap
2 GND Signal and Power ground pin. Place the bottom resistor of the feedback
3 FB Feedback pin. Connect FB to the external resistor divider to set output
4 EN Enable control input. Logic high enables operation. Do not allow this pin to
5 V 6 SW Output switch. Connects to the inductor, catch diode, and bootstrap
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.
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PIN DESCRIPTIONS
capacitor is connected between the BOOST and SW pins.
network as close as possible to this pin for accurate regulation.
voltage.
float or be greater than VIN+ 0.3V.
IN
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Input supply voltage. Connect a bypass capacitor to this pin.
capacitor.
LM2734
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Absolute Maximum Ratings
V
IN
(1)(2)
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
-0.5V to 24V SW Voltage -0.5V to 24V Boost Voltage -0.5V to 30V Boost to SW Voltage -0.5V to 6.0V FB Voltage -0.5V to 3.0V EN Voltage -0.5V to (VIN+ 0.3V) Junction Temperature 150°C ESD Susceptibility
(3)
2kV Storage Temp. Range -65°C to 150°C Soldering Information Reflow Peak Pkg. Temp.(15sec) 260°C
(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 ensured. For specific specifications and the test conditions, see Electrical Characteristics.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) Human body model, 1.5kΩ in series with 100pF.
Operating Ratings
V
IN
(1)
3V to 20V SW Voltage -0.5V to 20V Boost Voltage -0.5V to 25V Boost to SW Voltage 1.6V to 5.5V Junction Temperature Range −40°C to +125°C Thermal Resistance θ
(2)
JA
118°C/W
(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 ensured. For specific specifications and the test conditions, see Electrical Characteristics.
(2) Thermal shutdown will occur if the junction temperature exceeds 165°C. The maximum power dissipation is a function of T
and TA. The maximum allowable power dissipation at any ambient temperature is PD= (T 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
– TA)/θJA. All numbers apply for
J(MAX)
J(MAX)
, θ
JA
air, θJA= 204°C/W.
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LM2734
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
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Electrical Characteristics
Specifications with standard typeface are for TJ= 25°C, and those in boldface type apply over the full Operating Temperature Range (TJ= -40°C to 125°C). VIN= 5V, V
specification limits are ensured by design, test, or statistical analysis.
Symbol Parameter Conditions Min
V
ΔVFB/ΔVINFeedback Voltage Line Regulation VIN= 3V to 20V 0.01 % / V
I
FB
UVLO Undervoltage Lockout VINFalling 2.0 2.3 V
F
SW
D
MAX
D
MIN
R
DS(ON)
I
CL
I
I
BOOST
V
EN_TH
I
EN
I
SW
Feedback Voltage 0.784 0.800 0.816 V
FB
Feedback Input Bias Current Sink/Source 10 250 nA Undervoltage Lockout VINRising 2.74 2.90
UVLO Hysteresis 0.30 0.44 0.62
Switching Frequency MHz
Maximum Duty Cycle %
Minimum Duty Cycle %
Switch ON Resistance V Switch Current Limit V Quiescent Current Switching 1.5 2.5 mA
Q
LM2734X 1.2 1.6 1.9 LM2734Y 0.40 0.55 0.66 LM2734X 85 92 LM2734Y 90 96 LM2734X 2 LM2734Y 1
BOOST BOOST
Quiescent Current (shutdown) VEN= 0V 30 nA
Boost Pin Current mA
LM2734X (50% Duty Cycle) 2.5 3.5
LM2734Y (50% Duty Cycle) 1.0 1.8 Shutdown Threshold Voltage VENFalling 0.4 Enable Threshold Voltage VENRising 1.8 Enable Pin Current Sink/Source 10 nA Switch Leakage 40 nA
- VSW= 5V unless otherwise specified. Datasheet min/max
BOOST
(1)
Typ
(2)
Max
(1)
- VSW= 3V 300 600 mΩ
- VSW= 3V 1.2 1.7 2.5 A
Units
V
(1) Specified to Average Outgoing Quality Level (AOQL). (2) Typicals represent the most likely parametric norm.
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LM2734
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All curves taken at VIN= 5V, V
Efficiency vs Load Current - "X" V
Efficiency vs Load Current - "X" V
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
Typical Performance Characteristics
- VSW= 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified
BOOST
= 5V Efficiency vs Load Current - "Y" V
OUT
Figure 5. Figure 6.
= 3.3V Efficiency vs Load Current - "Y" V
OUT
otherwise.
OUT
OUT
= 5V
= 3.3V
Figure 7. Figure 8.
Efficiency vs Load Current - "X" V
Figure 9. Figure 10.
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= 1.5V Efficiency vs Load Current - "Y" V
OUT
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OUT
= 1.5V
LM2734
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
Typical Performance Characteristics (continued)
All curves taken at VIN= 5V, V otherwise.
Oscillator Frequency vs Temperature - "X" Oscillator Frequency vs Temperature - "Y"
Current Limit vs Temperature Current Limit vs Temperature
- VSW= 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified
BOOST
Figure 11. Figure 12.
VIN= 5V VIN= 20V
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Figure 13. Figure 14.
VFBvs Temperature R
Figure 15. Figure 16.
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vs Temperature
DSON
LM2734
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All curves taken at VIN= 5V, V otherwise.
IQSwitching vs Temperature V
Line Regulation - "Y" Line Regulation - "X"
V
= 1.5V, I
OUT
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
Typical Performance Characteristics (continued)
- VSW= 5V, L1 = 4.7 µH ("X"), L1 = 10 µH ("Y"), and TA= 25°C, unless specified
BOOST
Line Regulation - "X"
= 1.5V, I
OUT
Figure 17. Figure 18.
= 500mA V
OUT
OUT
= 3.3V, I
OUT
OUT
= 500mA
= 500mA
Figure 19. Figure 20.
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Line Regulation - "Y"
V
OUT
= 3.3V, I
OUT
= 500mA
Figure 21.
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L
R 1
R 2
D 1
D2
BOOST
Output Control
Logic
Current
Limit
Thermal
Shutdown
Under Voltage Lockout
Corrective Ramp
Reset Pulse
PWM Comparator
Current-Sense Amplifier
R
SENSE
+
+
Internal
Regulator
and
Enable
Circuit
Oscillator
Driver
0.3:
Switch
Internal
Compensation
SW
EN
FB
GND
Error Amplifier
-
+
V
REF
0.8V
C
OUT
ON
OFF
V
BOOST
I
L
V
SW
+
-
C
BOOST
V
OUT
C
IN
V
IN
V
IN
I
SENSE
+
-
+
-
+
-
0.88V
-
+
OVP
Comparator
Error
Signal
LM2734
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
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Block Diagram
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Figure 22.
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0
0
V
IN
V
D
T
ON
t
t
Inductor
Current
D = TON/T
SW
V
SW
T
OFF
T
SW
I
L
I
PK
SW
Voltage
LM2734
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SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
APPLICATION INFORMATION
THEORY OF OPERATION
The LM2734 is a constant frequency PWM buck regulator IC that delivers a 1A load current. The regulator has a preset switching frequency of either 550kHz (LM2734Y) or 1.6MHz (LM2734X). These high frequencies allow the LM2734 to operate with small surface mount capacitors and inductors, resulting in DC/DC converters that require a minimum amount of board space. The LM2734 is internally compensated, so it is simple to use, and requires few external components. The LM2734 uses current-mode control to regulate the output voltage.
The following operating description of the LM2734 will refer to the Simplified Block Diagram (Figure 22) and to the waveforms in Figure 23. The LM2734 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) increases with a linear slope. ILis measured by the current-sense amplifier, which generates an output proportional to the switch current. The sense signal is summed with the regulator’s corrective ramp and compared to the error amplifier’s output, which is proportional to the difference between the feedback voltage and V 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 forward voltage (VD) of the catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage.
. When the PWM comparator output goes high, the output switch turns off until the
REF
Figure 23. LM2734 Waveforms of SW Pin Voltage and Inductor Current
BOOST FUNCTION
Capacitor C drive voltage to the internal NMOS control switch. To properly drive the internal NMOS switch during its on-time, V
needs to be at least 1.6V greater than VSW. Although the LM2734 will operate with this minimum voltage,
BOOST
it may not have sufficient gate drive to supply large values of output current. Therefore, it is recommended that V
be greater than 2.5V above VSWfor best efficiency. V
BOOST
operating limit of 5.5V.
5.5V > V
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BOOST
and diode D2 in Figure 24 are used to generate a voltage V
BOOST
– VSW> 2.5V for best performance.
BOOST
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BOOST
. V
- VSWis the gate
BOOST
– VSWshould not exceed the maximum
LM2734
BOOST
SW
GND
L
D1
D2
C
OUT
C
BOOST
V
OUT
C
IN
V
IN
V
IN
V
BOOST
LM2734
SNVS288I –SEPTEMBER 2004–REVISED APRIIL 2013
Figure 24. V
Charges C
OUT
BOOST
When the LM2734 starts up, internal circuitry from the BOOST pin supplies a maximum of 20mA to C current charges C current to C
until the voltage at the feedback pin is greater than 0.76V.
BOOST
There are various methods to derive V
to a voltage sufficient to turn the switch on. The BOOST pin will continue to source
BOOST
:
BOOST
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BOOST
. This
1. From the input voltage (VIN)
2. From the output voltage (V
3. From an external distributed voltage rail (V
OUT
)
)
EXT
4. From a shunt or series zener diode
In the Simplifed Block Diagram of Figure 22, capacitor C NMOS switch. Capacitor C internal NMOS control switch is off (T (V
), during which the current in the inductor (L) forward biases the Schottky diode D1 (V
FD2
voltage stored across C
V
- VSW= VIN- V
BOOST
BOOST
FD2
is charged via diode D2 by VIN. During a normal switching cycle, when the
BOOST
) (refer to Figure 23), V
OFF
is
+ V
FD1
and diode D2 supply the gate-drive current for the
BOOST
equals VINminus the forward voltage of D2
BOOST
). Therefore the
FD1
(1)
When the NMOS switch turns on (TON), the switch pin rises to
VSW= VIN– (R
forcing V
V
BOOST
to rise thus reverse biasing D2. The voltage at V
BOOST
= 2VIN– (R
x IL), (2)
DSON
is then
BOOST
DSON
x IL) – V
FD2
+ V
FD1
(3)
which is approximately
2VIN- 0.4V (4)
for many applications. Thus the gate-drive voltage of the NMOS switch is approximately
VIN- 0.2V (5)
An alternate method for charging C
is to connect D2 to the output as shown in Figure 24. The output
BOOST
voltage should be between 2.5V and 5.5V, so that proper gate voltage will be applied to the internal switch. In this circuit, C
In applications where both VINand V directly from these voltages. If VINand V
provides a gate drive voltage that is slightly less than V
BOOST
are greater than 5.5V, or less than 3V, C
OUT
are greater than 5.5V, C
OUT
.
OUT
cannot be charged
can be charged from VINor V
BOOST
BOOST
OUT
minus a zener voltage by placing a zener diode D3 in series with D2, as shown in Figure 25. 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 V
(V (V
– VD3) < 5.5V
INMAX
– VD3) > 1.6V
INMIN
BOOST
voltage.
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