Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - voltage regulators - DC DC switch controllers VSSOP 8

LM3478

LM3478-Q1

www.ti.com

SNVS085V –JULY 2000–REVISED FEBRUARY 2013

High-Efficiency Low-Side N-Channel Controller for Switching Regulator

Check for Samples: LM3478, LM3478-Q1

FEATURES

APPLICATIONS

• LM3478Q in VSSOP-8 package is AEC-Q100

• Distributed Power Systems

qualified and manufactured on an Automotive

• Battery Chargers

Grade Flow

• Offline Power Supplies

• 8-lead VSSOP-8 and SOIC-8 packages

• Telecom Power Supplies

• Internal push-pull driver with 1A peak current

• Automotive Power Systems

capability

• Current limit and thermal shutdown

KEY SPECIFICATIONS

• Frequency compensation optimized with a

• Wide supply voltage range of 2.97V to 40V

capacitor and a resistor

• 100kHz to 1MHz Adjustable clock frequency

• Internal soft start

• ±2.5% (over temperature) internal reference

• Current Mode Operation

• 10µA shutdown current (over temperature)

• Undervoltage Lockout with hysteresis

DESCRIPTION

The LM3478 is a versatile Low-Side N-Channel MOSFET controller for switching regulators. It is suitable for use

in topologies requiring a low side MOSFET, such as boost, flyback, SEPIC, etc. Moreover, the LM3478 can be

operated at extremely high switching frequency in order to reduce the overall solution size. The switching

frequency of the LM3478 can be adjusted to any value between 100kHz and 1MHz by using a single external

resistor. Current mode control provides superior bandwidth and transient response, besides cycle-by-cycle

current limiting. Output current can be programmed with a single external resistor.

The LM3478 has built in features such as thermal shutdown, short-circuit protection, over voltage protection, etc.

Power saving shutdown mode reduces the total supply current to 5µA and allows power supply sequencing.

Internal soft-start limits the inrush current at start-up.

Typical Application Circuit

Figure 1. Typical High Efficiency Step-Up (Boost) Converter

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 (32 pages)

PAGE 1
LM3478 LM3478-Q1 www.ti.
PAGE 2
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Connection Diagram Figure 2. 8-Lead VSSOP-8 Package Figure 3. 8-Lead SOIC-8 Package Table 1. Pin Descriptions Pin Name Pin No. ISEN 1 Current sense input pin. Voltage generated across an external sense resistor is fed into this pin. Description COMP 2 Compensation pin. A resistor, capacitor combination connected to this pin provides compensation for the control loop. FB 3 Feedback pin.
PAGE 3
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 Electrical Characteristics Specifications in Standard type face are for TJ = 25°C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, VIN = 12V, RFA = 40kΩ Symbol VFB Parameter Feedback Voltage Conditions Typical VCOMP = 1.4V, 2.97 ≤ VIN ≤ 40V 1.26 Limit Unit 1.2416/1.228 1.2843/1.292 V V(min) V(max) ΔVLINE Feedback Voltage Line Regulation 2.97 ≤ VIN ≤ 40V 0.
PAGE 4
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Electrical Characteristics (continued) Specifications in Standard type face are for TJ = 25°C, and in bold type face apply over the full Operating Temperature Range. Unless otherwise specified, VIN = 12V, RFA = 40kΩ Symbol Gm AVOL IEAO Parameter Conditions Typical Error Amplifier Transconductance VCOMP = 1.4V IEAO = 100µA (Source/Sink) 800 Error Amplifier Voltage Gain VCOMP = 1.
PAGE 5
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 Typical Performance Characteristics Unless otherwise specified, VIN = 12V, TJ = 25°C. IQ vs Input Voltage (Shutdown) ISupply vs Input Voltage (Non-Switching) Figure 4. Figure 5. ISupply vs VIN (Switching) Switching Frequency vs RFA Figure 6. Figure 7. Frequency vs Temperature Drive Voltage vs Input Voltage Figure 8. Figure 9.
PAGE 6
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. 6 Current Sense Threshold vs Input Voltage COMP Pin Voltage vs Load Current Figure 10. Figure 11. Efficiency vs Load Current (3.3V In and 12V Out) Efficiency vs Load Current (5V In and 12V Out) Figure 12. Figure 13. Efficiency vs Load Current (9V In and 12V Out) Efficiency vs Load Current (3.3V In and 5V Out) Figure 14.
PAGE 7
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 Typical Performance Characteristics (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. Error Amplifier Gain Error Amplifier Phase Figure 16. Figure 17. COMP Pin Source Current vs Temperature Short Circuit Sense Voltage vs Input Voltage Figure 18. Figure 19. Compensation Ramp vs Compensation Resistor Shutdown Threshold Hysteresis vs Temperature Figure 20. Figure 21.
PAGE 8
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. Duty Cycle vs Current Sense Voltage Figure 22. FUNCTIONAL BLOCK DIAGRAM VIN FA/SD Fixed Frequency Detect Oscillator Softstart internal slope compensation Under Voltage Lockout LDO 1.26V Reference COMP 7.
PAGE 9
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 FUNCTIONAL DESCRIPTION The LM3478 uses a fixed frequency, Pulse Width Modulated (PWM) current mode control architecture. The block diagram above shows the basic functionality. In a typical application circuit, the peak current through the external MOSFET is sensed through an external sense resistor. The voltage across this resistor is fed into the ISEN pin. This voltage is fed into the positive input of the PWM comparator.
PAGE 10
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com VIN (V) 7.2V t VFB (V) OVP (1.31V) 1.26V t Figure 24. The Feedback Voltage Experiences an Oscillation if the Input Voltage crosses the 7.2V Internal Bias Threshold Blank-Out prevents false reset PWM Comparator resets the RS latch 92 mV typ + PWM Comparator Oscillator Sets the RS Latch 325 ns Blank-Out time Figure 25. Basic Operation of the PWM Comparator SLOPE COMPENSATION RAMP The LM3478 uses a current mode control scheme.
PAGE 11
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 Voltage VC PWM Comparator Waveforms Se 'I0 VSEN 'I2 Sn Sf 'I1 Time Figure 26. Sub-Harmonic Oscillation for D>0.5 and Compensation Ramp to Avoid Sub-Harmonic Oscillation Sub-harmonic Oscillation can be easily understood as a geometric problem. If the control signal does not have slope, the slope representing the inductor current ramps up until the control signal is reached and then slopes down again.
PAGE 12
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 DR www.ti.com Q LM3478 ISEN RSL RSEN Figure 27. Adding External Slope Compensation Figure 28. External Slope Compensation ΔVSL vs RSL FREQUENCY ADJUST/SHUTDOWN The switching frequency of the LM3478 can be adjusted between 100kHz and 1MHz using a single external resistor. This resistor must be connected between FA/SD pin and ground, as shown in Figure 29.
PAGE 13
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 Figure 30. Shutdown Operation in Frequency Adjust Mode SHORT-CIRCUIT PROTECTION When the voltage across the sense resistor measured on the ISEN pin exceeds 343 mV, short circuit current limit protection gets activated. A comparator inside the LM3478 reduces the switching frequency by a factor of 5 and maintains this condition until the short is removed. In normal operation the sensed current will trigger the power MOSFET to turn off.
PAGE 14
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Figure 31. Simplified Boost Converter (a) First Cycle Operation (b) Second Cycle of Operation POWER INDUCTOR SELECTION The inductor is one of the two energy storage elements in a boost converter. Figure 32 shows how the inductor current varies during a switching cycle.
PAGE 15
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 IL (A) VIN L VIN VOUT L 'iL IL_AVG t (s) D*Ts Ts (a) ID (A) VIN - V OUT L ID_AVG =IOUT_AVG t (s) D*Ts Ts (b) ISW (A) VIN L ISW_AVG t (s) D*Ts Ts (C) Figure 32.
PAGE 16
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com PROGRAMMING THE OUTPUT VOLTAGE The output voltage can be programmed using a resistor divider between the output and the FB pin. The resistors are selected such that the voltage at the FB pin is 1.26V. Pick RF1 (the resistor between the output voltage and the feedback pin) and RF2 (the resistor between the feedback pin and ground) can be selected using the following equation, RF2 = (1.26V x RF1) / (Vout - 1.
PAGE 17
LM3478 LM3478-Q1 www.ti.com RSEN = SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 VSENSE - (D x VSENSE x VSLratio) ISWLIMIT (19) RSEN is part of the current mode control loop and has some influence on control loop stability. Therefore, once the current limit threshold is set, loop stability must be verified.
PAGE 18
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com POWER MOSFET SELECTION The drive pin of the LM3478 must be connected to the gate of an external MOSFET. The drive pin (DR) voltage depends on the input voltage (see typical performance characteristics). In most applications, a logic level MOSFET can be used. For very low input voltages, a sub logic level MOSFET should be used. The selected MOSFET has a great influence on the system efficiency.
PAGE 19
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 OUTPUT CAPACITOR SELECTION The output capacitor in a boost converter provides all the output current when the inductor is charging. As a result it sees very large ripple currents. The output capacitor should be capable of handling the maximum RMS current. The RMS current in the output capacitor is: (32) Where (33) The ESR and ESL of the capacitor directly control the output ripple.
PAGE 20
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Figure 35. Current Flow In A Boost Application The PGND and AGND pins have to be connected to the same ground very close to the IC. To avoid ground loop currents, attach all the grounds of the system only at one point. A ceramic input capacitor should be connected as close as possible to the Vin pin and grounded close to the GND pin. For a layout example please see AN-1204.
PAGE 21
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 Figure 36. Typical SEPIC Converter POWER MOSFET SELECTION As in a boost converter, parameters governing the selection of the MOSFET are the minimum threshold voltage, VTH(MIN), the on-resistance, RDS(ON), the total gate charge, Qg, the reverse transfer capacitance, CRSS, and the maximum drain to source voltage, VDS(MAX).
PAGE 22
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com (41) (42) Maintaining the condition IL > ΔiL/2 to ensure continuous current conduction yields: (VIN - VQ)(1-D) L1 > 2IOUTfS L2 > (43) (VIN - VQ)D 2IOUTfS (44) Peak current in the inductor, to ensure the inductor does not saturate: (45) (46) IL1PK must be lower than the maximum current rating set by the current sense resistor.
PAGE 23
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 (51) is the ripple voltage across the SEPIC capacitor, and (52) is the ripple current through the inductor L1. The energy balance equation can be solved to provide a minimum value for CS: (53) Input Capacitor Selection Similar to a boost converter, the SEPIC has an inductor at the input. Hence, the input current waveform is continuous and triangular. The inductor ensures that the input capacitor sees fairly low ripple currents.
PAGE 24
LM3478 LM3478-Q1 SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 www.ti.com Other Application Circuits Figure 37. Typical Flyback Circuit RBYP 10: RSL 604: CSEN 10 nF CC2 0.47 PF ISEN RC 100: VIN CC 1 PF FB VIN = from 5V to 0.5V L1 3.3 PH + CIN 2 x 10 PF, 16V MBRS130LT3 VOUT = 9V, 20 mA D1 COUT 3 x 10 PF, 16V FA/SD COMP RFB1 10 k: RFA 71.5 k: D2 BAT54C-7-F LM3478 Q1 FDS6690A DR AGND PGND CHF 10 nF CBYP 100 nF RFB2 61.9 k: RSEN 0.03: Figure 38.
PAGE 25
LM3478 LM3478-Q1 www.ti.com SNVS085V – JULY 2000 – REVISED FEBRUARY 2013 REVISION HISTORY Changes from Revision U (February 2013) to Revision V • Page Changed layout of National Data Sheet to TI format ..........................................................................................................
PAGE 26
PACKAGE OPTION ADDENDUM www.ti.
PAGE 27
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 28
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 LM3478MAX/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LM3478MM VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3478MM/NOPB VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.
PAGE 29
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) LM3478MAX/NOPB SOIC D 8 2500 367.0 367.0 35.0 LM3478MM VSSOP DGK 8 1000 210.0 185.0 35.0 LM3478MM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM3478MMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0 LM3478QMM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM3478QMMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.
PAGE 30
PAGE 31
PAGE 32
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.