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BST

COMP

RAMP

VCC

VIN

OUT

GND

LM25576

VIN

VOUT

SYNC

LM25576, LM25576-Q1

www.ti.com

SNVS470G –JANUARY 2007–REVISED APRIL 2013

LM25576/LM25576-Q1 SIMPLE SWITCHER® 42V, 3A Step-Down Switching Regulator

Check for Samples: LM25576, LM25576-Q1

FEATURES

DESCRIPTION

The LM25576 is an easy to use SIMPLE

• LM25576-Q1 is an Automotive Grade Product

SWITCHER® buck regulator which allows design

that is AEC-Q100 Grade 1 Qualified (−40°C to +

engineers to design and optimize a robust power

125°C Operating Junction Temperature)

supply using a minimum set of components.

• Integrated 42V, 170mΩ N-channel MOSFET

Operating with an input voltage range of 6 - 42V, the

LM25576 delivers 3A of continuous output current

• Ultra-Wide Input Voltage Range from 6V to 42V

with an integrated 170mΩ N-Channel MOSFET. The

• Adjustable Output Voltage as Low as 1.225V

regulator utilizes an Emulated Current Mode

• 1.5% Feedback Reference Accuracy

architecture which provides inherent line regulation,

• Operating Frequency Adjustable Between

tight load transient response, and ease of loop

compensation without the usual limitation of low-duty

50kHz and 1MHz with Single Resistor

cycles associated with current mode regulators. The

• Master or Slave Frequency Synchronization

operating frequency is adjustable from 50kHz to

• Adjustable Soft-Start

1MHz to allow optimization of size and efficiency. To

• Emulated Current Mode Control Architecture reduce EMI, a frequency synchronization pin allows

multiple IC’s from the LM(2)557x family to self-

• Wide Bandwidth Error Amplifier

synchronize or to synchronize to an external clock.

• Built-in Protection

The LM25576 ensures robustness with cycle-by-cycle

• Automotive Grade Product Datasheet that is

current limit, short-circuit protection, thermal shut-

down, and remote shut-down. The device is available

AEC-Q100 Grade 0 Qualified is Available Upon

in a power enhanced HTSSOP-20 package featuring

Request.

an exposed die attach pad for thermal dissipation.

– (−40°C to + 150°C Operating Junction

The LM25576 is supported by the full suite of

Temperature)

WEBENCH

On-Line design tools.

APPLICATIONS

PACKAGE

• Automotive

• HTSSOP-20EP (Exposed Pad)

• Industrial

Simplified Application Schematic

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.

3All 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.

Summary of content (29 pages)

PAGE 1
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 LM25576/LM25576-Q1 SIMPLE SWITCHER® 42V, 3A Step-Down Switching Regulator Check for Samples: LM25576, LM25576-Q1 FEATURES DESCRIPTION • The LM25576 is an easy to use SIMPLE SWITCHER® buck regulator which allows design engineers to design and optimize a robust power supply using a minimum set of components.
PAGE 2
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Connection Diagram 1 VCC BST SD PRE VIN SW VIN SW 2 3 4 5 6 7 8 9 10 SYNC IS COMP IS FB PGND RT PGND RAMP OUT AGND SS 20 19 18 17 16 15 14 13 12 11 Figure 1. Top View 20-Lead HTSSOP Pin Descriptions 2 Pin(s) Name 1 VCC 2 Description Application Information Output of the bias regulator Vcc tracks Vin up to 9V. Beyond 9V, Vcc is regulated to 7 Volts. A 0.
PAGE 3
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 Pin Descriptions (continued) Pin(s) Name 17, 18 SW Switching node Description The source terminal of the internal buck switch. The SW pin should be connected to the external Schottky diode and to the buck inductor.
PAGE 4
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Temperature range. VIN = 24V, RT = 32.4kΩ unless otherwise stated. (1) Symbol Parameter Conditions Min Typ Max Units 6.85 7.15 7.
PAGE 5
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 Electrical Characteristics (continued) Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Temperature range. VIN = 24V, RT = 32.4kΩ unless otherwise stated.
PAGE 6
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Typical Performance Characteristics Oscillator Frequency vs Temperature FOSC = 200kHz Oscillator Frequency vs RT NORMALIZED OSCILLATOR FREQUENCY OSCILLATOR FREQUENCY (kHz) 1000 100 10 1 10 100 1000 1.010 1.005 1.000 0.995 0.990 -50 -25 0 25 50 75 100 125 RT (k:) o TEMPERATURE ( C) Figure 2. Figure 3. Soft Start Current vs Temperature VCC vs ICC VIN = 12V 8 6 1.
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LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 Typical Performance Characteristics (continued) Demoboard Efficiency vs IOUT and VIN 100 VIN = 7V 90 EFFICIENCY (%) 80 VIN = 24V 70 60 50 40 30 20 10 0 0.5 1 1.5 2 2.5 3 IOUT (A) Figure 8.
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LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com TYPICAL APPLICATION CIRCUIT AND BLOCK DIAGRAM VIN 7V ± 42V C1 2.2 3, 4 VIN C2 2.2 7V REGULATOR 5 PA R1 OPEN LM25576 1.225V 2 SD STANDBY VCC SHUTDOWN 0.7V SD C12 OPEN R2 OPEN 11 SS BST UVLO C7 0.022 DRIVER S Q 1.225V 20 VIN DIS CLK 10 PA C4 0.01 C8 0.47 THERMAL SHUTDOWN UVLO 1 R Q LEVEL SHIFT PWM 0.7V PRE 19 C_LIMIT 7 FB C6 open C5 0.01 R4 49.9k ERROR AMP 0.
PAGE 9
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 An auxiliary supply voltage can be applied to the VCC pin to reduce the IC power dissipation. If the auxiliary voltage is greater than 7.3V, the internal regulator will essentially shut off, reducing the IC power dissipation. The Vcc regulator series pass transistor includes a diode between Vcc and Vin that should not be forward biased in normal operation. Therefore the auxiliary Vcc voltage should never exceed the Vin voltage.
PAGE 10
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com LM25576 SYNC SW SYNC AGND CLK SW 500 ns Figure 11. Sync from External Clock LM25576 SYNC LM25576 SYNC UP TO 5 TOTAL DEVICES Figure 12. Sync from Multiple Devices Multiple LM25576 devices can be synchronized together simply by connecting the SYNC pins together. In this configuration all of the devices will be synchronized to the highest frequency device.
PAGE 11
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 Error Amplifier and PWM Comparator The internal high gain error amplifier generates an error signal proportional to the difference between the regulated output voltage and an internal precision reference (1.225V). The output of the error amplifier is connected to the COMP pin allowing the user to provide loop compensation components, generally a type II network, as illustrated in Figure 9.
PAGE 12
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Proper selection of the RAMP capacitor depends upon the selected value of the output inductor. The value of CRAMP can be selected from: CRAMP = L x 10-5, where L is the value of the output inductor in Henrys. With this value, the scale factor of the emulated current ramp will be approximately equal to the scale factor of the DC level sample and hold ( 0.5 V / A).
PAGE 13
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 Soft-Start The soft-start feature allows the regulator to gradually reach the initial steady state operating point, thus reducing start-up stresses and surges. The internal soft-start current source, set to 10µA, gradually increases the voltage of an external soft-start capacitor connected to the SS pin. The soft-start capacitor voltage is connected to the reference input of the error amplifier.
PAGE 14
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com L1 Current IPK+ IRIPPLE IO IPK- 1/Fs 0 mA Figure 16. Inductor Current Waveform To keep the circuit in continuous conduction mode (CCM), the maximum ripple current IRIPPLE should be less than twice the minimum load current, or 0.5Ap-p. Using this value of ripple current, the value of inductor (L1) is calculated using the following: L1 = VOUT x (VIN(max) ± VOUT) IRIPPLE x FS x VIN(max) (6) 5V x (42V ± 5V) L1 = = 29 PH 0.
PAGE 15
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 The forward voltage drop has a significant impact on the conversion efficiency, especially for applications with a low output voltage. “Rated” current for diodes vary widely from various manufacturers. The worst case is to assume a short circuit load condition. In this case the diode will carry the output current almost continuously. For the LM25576 this current can be as high as 4.2A.
PAGE 16
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Capacitor C12 provides filtering for the divider. The voltage at the SD pin should never exceed 8V, when using an external set-point divider it may be necessary to clamp the SD pin at high input voltage conditions. The reference design utilizes the full range of the LM25576 (6V to 42V); therefore these components can be omitted. With the SD pin open circuit the LM25576 responds once the Vcc UVLO threshold is satisfied.
PAGE 17
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 Components R4 and C5 configure the error amplifier as a type II configuration which has a pole at DC and a zero at fZ = 1 / (2πR4C5). The error amplifier zero cancels the modulator pole leaving a single pole response at the crossover frequency of the loop gain. A single pole response at the crossover frequency yields a very stable loop with 90 degrees of phase margin.
PAGE 18
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com If a network analyzer is available, the modulator gain can be measured and the error amplifier gain can be configured for the desired loop transfer function. If a network analyzer is not available, the error amplifier compensation components can be designed with the guidelines given. Step load transient tests can be performed to verify acceptable performance. The step load goal is minimum overshoot with a damped response.
PAGE 19
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 PCB LAYOUT AND THERMAL CONSIDERATIONS The circuit in Figure 21 serves as both a block diagram of the LM25576 and a typical application board schematic for the LM25576. In a buck regulator there are two loops where currents are switched very fast. The first loop starts from the input capacitors, to the regulator VIN pin, to the regulator SW pin, to the inductor then out to the load.
PAGE 20
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Table 1. 5V, 3A Demo Board Bill of Materials ITEM 20 PART NUMBER DESCRIPTION VALUE C 1 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µ, 100V C 2 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µ, 100V C 3 C0805C331G1GAC CAPACITOR, CER, KEMET 330p, 100V C 4 C2012X7R2A103K CAPACITOR, CER, TDK 0.01µ, 100V C 5 C2012X7R2A103K CAPACITOR, CER, TDK 0.01µ, 100V C 6 OPEN NOT USED C 7 C2012X7R2A223K CAPACITOR, CER, TDK 0.
PAGE 21
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 PCB Layout Figure 22. Component Side Figure 23. Solder Side Figure 24.
PAGE 22
LM25576, LM25576-Q1 SNVS470G – JANUARY 2007 – REVISED APRIL 2013 www.ti.com Typical Schematic for High Frequency (1MHz) Application BST 9V - 32V 0.022P VIN 3.3V, 3A SD 3.3P 4.7P SW 5.11k SYNC CSHD6-40 COMP LM25576 140P IS 49.9k 3.01k GND 0.01P OUT FB RAMP RT SS VCC 3.57k 0.1P 47p 0.01P Figure 25. Schematic 3.3V, 3A, 1MHz Typical Schematic for Buck/Boost (Inverting) Application BST 0.022 33P 10V - 30V SW VIN LM25576 4.4 7.
PAGE 23
LM25576, LM25576-Q1 www.ti.com SNVS470G – JANUARY 2007 – REVISED APRIL 2013 REVISION HISTORY Changes from Revision F (April 2013) to Revision G • Page Changed layout of National Data Sheet to TI format ..........................................................................................................
PAGE 24
PACKAGE OPTION ADDENDUM www.ti.
PAGE 25
PACKAGE OPTION ADDENDUM www.ti.com 1-Nov-2013 (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line.
PAGE 26
PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-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) LM25576MHX HTSSOP PWP 20 2500 330.0 16.4 LM25576MHX/NOPB B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 6.95 7.1 1.6 8.0 16.0 Q1 HTSSOP PWP 20 2500 330.0 16.4 6.95 7.1 1.6 8.0 16.0 Q1 LM25576Q0MHX/NOPB HTSSOP PWP 20 2500 330.0 16.4 6.95 7.1 1.6 8.0 16.
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PACKAGE MATERIALS INFORMATION www.ti.com 8-Apr-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM25576MHX HTSSOP PWP 20 2500 367.0 367.0 35.0 LM25576MHX/NOPB HTSSOP PWP 20 2500 367.0 367.0 35.0 LM25576Q0MHX/NOPB HTSSOP PWP 20 2500 367.0 367.0 35.0 LM25576QMHX/NOPB HTSSOP PWP 20 2500 367.0 367.0 35.
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MECHANICAL DATA PWP0020A MXA20A (Rev C) www.ti.
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