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LM34914

BST

ISEN

RON/SD

SHUT

DOWN

RTN

SGND

8V - 40V

Input

R1 R3

OUT

LM34914

www.ti.com

SNVS453B –MAY 2006–REVISED MARCH 2013

LM34914 Ultra Small 1.25A Step-Down Switching Regulator with Intelligent Current Limit

Check for Samples: LM34914

FEATURES

DESCRIPTION

The LM34914 Step-Down Switching Regulator

• Input Voltage Range: 8V to 40V

features all the functions needed to implement a low

• Integrated N-Channel Buck Switch

cost, efficient, buck bias regulator capable of

• Valley Current Limit Varies with V

and V

OUT

supplying at least 1.25A to the load. To reduce

to Reduce Excessive Inductor Current

excessive switch current due to the possibility of a

saturating inductor the valley current limit threshold

• On-time is Reduced when in Current Limit

changes with input and output voltages, and the on-

• Integrated Start-Up Regulator

time is reduced when current limit is detected. This

• No Loop Compensation Required

buck regulator contains a 44V N-Channel Buck

Switch, and is available in the thermally enhanced 3

• Ultra-Fast Transient Response

mm x 3 mm WSON-10 package. The feedback

• Maximum Switching Frequency: 1.3 MHz

regulation scheme requires no loop compensation,

• Operating Frequency Remains Nearly

results in fast load transient response, and simplifies

Constant with Load Current and Input Voltage

circuit implementation. The operating frequency

Variations remains constant with line and load variations due to

the inverse relationship between the input voltage

• Programmable Soft-Start

and the on-time. The valley current limit results in a

• Precision Internal Reference

smooth transition from constant voltage to constant

• Adjustable Output Voltage

current mode when current limit is detected, reducing

the frequency and output voltage, without the use of

• Thermal Shutdown

foldback. Additional features include: VCC under-

voltage lock-out, thermal shutdown, gate drive under-

TYPICAL APPLICATIONS

voltage lock-out, and maximum duty cycle limit.

• High Efficiency Point-Of-Load (POL) Regulator

Package

• Non-Isolated Buck Regulator

• WSON-10 (3 mm x 3mm)

• Secondary High Voltage Post Regulator

• Exposed Thermal Pad For Improved Heat

Dissipation

Basic Step Down Regulator

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.

2All 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.

Summary of content (21 pages)

PAGE 1
LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 LM34914 Ultra Small 1.25A Step-Down Switching Regulator with Intelligent Current Limit Check for Samples: LM34914 FEATURES DESCRIPTION • • • The LM34914 Step-Down Switching Regulator features all the functions needed to implement a low cost, efficient, buck bias regulator capable of supplying at least 1.25A to the load.
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LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com Connection Diagram 1 2 3 4 5 10 SW VIN BST VCC ISEN RON/SD SGND SS RTN FB 9 8 7 6 10-Lead WSON PIN DESCRIPTIONS Pin Number Name Description Application Information 1 SW Switching Node Internally connected to the buck switch source. Connect to the inductor, diode, and bootstrap capacitor. 2 BST Boost pin for bootstrap capacitor Connect a 0.022 µF capacitor from SW to this pin.
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LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 Absolute Maximum Ratings (1) (2) VIN to RTN 44V BST to RTN 52V SW to RTN (Steady State) -1.5V BST to VCC 44V VIN to SW 44V BST to SW 14V VCC to RTN 14V SGND to RTN -0.3V to +0.3V Current out of ISEN See text SS to RTN -0.3V to 4V All Other Inputs to RTN -0.
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LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com Electrical Characteristics (continued) Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are specified 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.
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LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 Typical Performance Characteristics Unless otherwise specified the following conditions apply: TJ = 25°C Typical Efficiency Performance VCC vs VIN 100 7.5 Vin = 8V 95 90 24V VCC (V) EFFICIENCY (%) 7.0 12V 85 40V 80 75 6.5 6.0 5.5 VOUT = 5V FS = 275 kHz 70 0 200 400 600 800 5.0 1000 6.5 7.0 7.5 8.0 8.5 9.0 LOAD CURRENT (mA) VIN (V) Figure 1. Figure 2.
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LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified the following conditions apply: TJ = 25°C Input Shutdown and Operating Current Into VIN INPUT CURRENT (PA) 800 600 Operating Current 400 200 Shutdown Current 0 0 10 20 30 40 VIN (V) Figure 7.
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LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 Typical Application Circuit and Block Diagram Input 8V - 40V 7V START-UP REGULATOR VIN C5 LM34914 VCC VCC THERMAL SHUTDOWN C3 UVLO C1 ON TIMER GND RON RON START ' Ton FINISH RON/SD MINIMUM OFF TIMER START FINISH 0.8V BST Gate Drive SD UVLO 2.5V SS 12.5 PA VIN C4 LOGIC LEVEL SHIFT Driver C6 L1 SW FB REGULATION COMPARATOR 2.
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LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com VIN 7.0V UVLO VCC SW Pin Inductor Current 2.5V SS Pin VOUT t1 t2 Figure 8. Startup Sequence Functional Description The LM34914 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient buck bias power converter capable of supplying at least 1.25A to the load.
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LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 When in regulation, the LM34914 operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. In continuous conduction mode the inductor’s current is always greater than zero, and the operating frequency remains relatively constant with load and line variations. The minimum load current for continuous conduction mode is one-half the inductor’s ripple current amplitude.
PAGE 10
LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com Shutdown The LM34914 can be remotely shut down by taking the RON/SD pin below 0.8V. See Figure 9. In this mode the SS pin is internally grounded, the on-timer is disabled, and bias currents are reduced. Releasing the RON/SD pin allows the circuit to resume operation. The voltage at the RON/SD pin is normally between 1.5V and 3.0V, depending on VIN and the RON resistor. VIN Input Voltage RON LM34914 RON/SD STOP RUN Figure 9.
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LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 Inductor Current IOUT2 Current Limit Threshold IOUT3 TON 'I 2 IOUT1 Feedback Voltage @ FB Pin TON 2.5V Normal Operation Load Current Increases Current Limited Normal Operation Load Current Decreases Figure 10. Inductor Current - Normal and Current Limit Operation N - Channel Buck Switch and Driver The LM34914 integrates an N-Channel buck switch and associated floating high voltage gate driver.
PAGE 12
LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com APPLICATIONS INFORMATION EXTERNAL COMPONENTS The following guidelines can be used to select the external components (see the Block Diagram). First determine the following operating parameters: - Output voltage (VOUT) - Minimum and maximum input voltage (VIN(min) and VIN(max)) - Minimum and maximum load current (IOUT(min) and IOUT(max)) - Switching Frequency (FS) R1 and R2: These resistors set the output voltage.
PAGE 13
LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 D1: A Schottky diode is recommended. Ultra-fast recovery diodes are not recommended as the high speed transitions at the SW pin may inadvertently affect the IC’s operation through external or internal EMI. The diode should be rated for the maximum input voltage (VIN(max)), the maximum load current (IOUT(max)), and the peak current which occurs when the current limit and maximum ripple current are reached simultaneously.
PAGE 14
LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com LOW OUTPUT RIPPLE CONFIGURATIONS For applications where low output ripple is required, the following options can be used to reduce or nearly eliminate the ripple. a) Reduced ripple configuration: In Figure 11, Cff is added across R1 to AC-couple the ripple at VOUT directly to the FB pin. This allows the ripple at VOUT to be reduced to a minimum of 25 mVp-p by reducing R3, since the ripple at VOUT is not attenuated by the feedback resistors.
PAGE 15
LM34914 www.ti.com SNVS453B – MAY 2006 – REVISED MARCH 2013 c) Alternate minimum ripple configuration: The circuit in Figure 13 is the same as that in the Block Diagram, except the output voltage is taken from the junction of R3 and C2. The ripple at VOUT is determined by the inductor’s ripple current and C2’s characteristics. However, R3 slightly degrades the load regulation. This circuit may be suitable if the load current is fairly constant. L1 SW LM34914 R1 R3 FB VOUT R2 C2 Figure 13.
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LM34914 SNVS453B – MAY 2006 – REVISED MARCH 2013 www.ti.com REVISION HISTORY Changes from Revision A (March 2013) to Revision B • 16 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM34914SD/NOPB WSON DSC 10 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 LM34914SDX/NOPB WSON DSC 10 4500 330.0 12.4 3.3 3.3 1.0 8.0 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 11-Oct-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM34914SD/NOPB WSON DSC 10 1000 210.0 185.0 35.0 LM34914SDX/NOPB WSON DSC 10 4500 367.0 367.0 35.
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MECHANICAL DATA DSC0010A SDA10A (Rev A) www.ti.
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