Datasheet

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

LM3488

LM3488-Q1

www.ti.com

SNVS089M –JULY 2000–REVISED MARCH 2013

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

Check for Samples: LM3488, LM3488-Q1

FEATURES

DESCRIPTION

The LM3488 is a versatile Low-Side N-FET high

• LM3488Q is AEC-Q100 qualified and

performance controller for switching regulators. It is

manufactured on an Automotive Grade Flow

suitable for use in topologies requiring low side FET,

• 8-lead VSSOP package

such as boost, flyback, or SEPIC. Moreover, the

• Internal push-pull driver with 1A peak current

LM3488 can be operated at extremely high switching

frequency in order to reduce the overall solution size.

capability

The switching frequency of LM3488 can be adjusted

• Current limit and thermal shutdown

to any value between 100kHz and 1MHz by using a

• Frequency compensation optimized with a

single external resistor or by synchronizing it to an

capacitor and a resistor

external clock. Current mode control provides

superior bandwidth and transient response, besides

• Internal softstart

cycle-by-cycle current limiting. Output current can be

• Current Mode Operation

programmed with a single external resistor.

• Undervoltage Lockout with hysteresis

The LM3488 has built in features such as thermal

shutdown, short-circuit protection and over voltage

APPLICATIONS

protection. Power saving shutdown mode reduces the

• Distributed Power Systems

total supply current to 5µA and allows power supply

sequencing. Internal soft-start limits the inrush current

• Notebook, PDA, Digital Camera, and other

at start-up.

Portable Applications

• Offline Power Supplies

KEY SPECIFICATIONS

• Set-Top Boxes

• Wide supply voltage range of 2.97V to 40V

• 100kHz to 1MHz Adjustable and

Synchronizable clock frequency

• ±1.5% (over temperature) internal reference

• 5µA shutdown current (over temperature)

TYPICAL APPLICATION CIRCUIT

Figure 1. Typical SEPIC 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 (33 pages)

PAGE 1
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 High Efficiency Low-Side N-Channel Controller for Switching Regulators Check for Samples: LM3488, LM3488-Q1 FEATURES DESCRIPTION • The LM3488 is a versatile Low-Side N-FET high performance controller for switching regulators. It is suitable for use in topologies requiring low side FET, such as boost, flyback, or SEPIC.
PAGE 2
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Connection Diagram Figure 2. 8-Lead VSSOP Package PIN DESCRIPTIONS Pin Name Pin No. Description ISEN 1 Current sense input pin. Voltage generated across an external sense resistor is fed into this pin. COMP 2 Compensation pin. A resistor, capacitor combination connected to this pin provides compensation for the control loop. FB 3 Feedback pin. The output voltage should be adjusted using a resistor divider to provide 1.
PAGE 3
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 Operating Ratings (1) 2.97V ≤ VIN ≤ 40V Supply Voltage −40°C ≤ TJ ≤ +125°C Junction Temperature Range 100kHz ≤ FSW ≤ 1MHz Switching Frequency (1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics.
PAGE 4
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 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 VOVP(HYS) Gm AVOL IEAO Parameter Conditions Typical Output Over-Voltage Protection Hysteresis (5) VCOMP = 1.4V Error Ampifier Transconductance VCOMP = 1.4V IEAO = 100µA (Source/Sink) 800 VCOMP = 1.
PAGE 5
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 Typical Performance Characteristics Unless otherwise specified, VIN = 12V, TJ = 25°C. IQ vs Temperature & Input Voltage ISupply vs Input Voltage (Non-Switching) Figure 3. Figure 4. ISupply vs VIN Switching Frequency vs RFA Figure 5. Figure 6.
PAGE 6
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. 6 Frequency vs Temperature Drive Voltage vs Input Voltage Figure 7. Figure 8. Current Sense Threshold vs Input Voltage COMP Pin Voltage vs Load Current Figure 9. Figure 10. Efficiency vs Load Current (3.3V In and 12V Out) Efficiency vs Load Current (5V In and 12V Out) Figure 11. Figure 12.
PAGE 7
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 Typical Performance Characteristics (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. Efficiency vs Load Current (9V In and 12V Out) Efficiency vs Load Current (3.3V In and 5V Out) Figure 13. Figure 14. Error Amplifier Gain Error Amplifier Phase Figure 15. Figure 16. COMP Pin Source Current vs Temperature Short Circuit Protection vs Input Voltage Figure 17. Figure 18.
PAGE 8
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Typical Performance Characteristics (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. Compensation Ramp vs Compensation Resistor Shutdown Threshold Hysteresis vs Temperature Figure 19. Figure 20. Current Sense Voltage vs Duty Cycle Figure 21.
PAGE 9
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION The LM3488 uses a fixed frequency, Pulse Width Modulated (PWM), current mode control architecture. 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 then level shifted and fed into the positive input of the PWM comparator.
PAGE 10
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Under extremely light load or no-load conditions, the energy delivered to the output capacitor when the external MOSFET is on during the blank-out time is more than what is delivered to the load. An over-voltage comparator inside the LM3488 prevents the output voltage from rising under these conditions. The over-voltage comparator senses the feedback (FB pin) voltage and resets the RS latch under these conditions.
PAGE 11
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 Figure 24. Compensation Ramp Avoids Sub-Harmonic Oscillation The compensation ramp has been added internally in LM3488. The slope of this compensation ramp has been selected to satisfy most of the applications. The slope of the internal compensation ramp depends on the frequency. This slope can be calculated using the formula: MC = VSL.FS Volts/second (3) In the above equation, VSL is the amplitude of the internal compensation ramp.
PAGE 12
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Figure 25. Increasing the Slope of the Compensation Ramp Figure 26. ΔVSL vs RSL FREQUENCY ADJUST/SYNCHRONIZATION/SHUTDOWN The switching frequency of LM3488 can be adjusted between 100kHz and 1MHz using a single external resistor. This resistor must be connected between FA/SYNC/SD pin and ground, as shown in Figure 27.
PAGE 13
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 The LM3488 can be synchronized to an external clock. The external clock must be connected to the FA/SYNC/SD pin through a resistor, RSYNC as shown in Figure 28. The value of this resistor is dependent on the off time of the synchronization pulse, TOFF(SYNC). Table 1 shows the range of resistors to be used for a given TOFF(SYNC). Table 1.
PAGE 14
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Figure 28. Frequency Synchronization Figure 29. Shutdown Operation in Frequency Adjust Mode Figure 30. Shutdown Operation in Synchronization Mode RSYNC CSYNC FA/SYNC/SD 270 pF LM3488 RFA Figure 31.
PAGE 15
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 SHORT-CIRCUIT PROTECTION When the voltage across the sense resistor (measured on ISEN Pin) exceeds 350mV, short-circuit current limit gets activated. A comparator inside LM3488 reduces the switching frequency by a factor of 5 and maintains this condition till the short is removed. TYPICAL APPLICATIONS The LM3488 may be operated in either continuous or discontinuous conduction mode.
PAGE 16
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Figure 32. Simplified Boost Converter Diagram (a) First cycle of operation (b) Second cycle of operation POWER INDUCTOR SELECTION The inductor is one of the two energy storage elements in a boost converter. Figure 33 shows how the inductor current varies during a switching cycle.
PAGE 17
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 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 33. A. Inductor Current B. Diode Current C. Switch Current If VL(t) is constant, diL(t)/dt must be constant. Hence, for a given input voltage and output voltage, the current in the inductor changes at a constant rate.
PAGE 18
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com The important quantities in determining a proper inductance value are IL (the average inductor current) and ΔiL (the inductor current ripple). If ΔiL is larger than IL, the inductor current will drop to zero for a portion of the cycle and the converter will operate in discontinuous conduction mode. If ΔiL is smaller than IL, the inductor current will stay above zero and the converter will operate in continuous conduction mode.
PAGE 19
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 VIN L D VOUT COUT Q DR LM3488 ISEN Rfb1 FB RSEN Rfb2 Figure 34. Adjusting the Output Voltage SETTING THE CURRENT LIMIT The maximum amount of current that can be delivered to the load is set by the sense resistor, RSEN. Current limit occurs when the voltage that is generated across the sense resistor equals the current sense threshold voltage, VSENSE.
PAGE 20
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 RSEN = www.ti.com VSENSE - (D x VSENSE x VSLratio) ISWLIMIT (18) 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 21
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 POWER MOSFET SELECTION The drive pin of LM3488 must be connected to the gate of an external MOSFET. In a boost topology, the drain of the external N-Channel MOSFET is connected to the inductor and the source is connected to the ground. The drive pin (DR) voltage depends on the input voltage (see Typical Performance Characteristics). In most applications, a logic level MOSFET can be used.
PAGE 22
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com RIN VIN CBYPASS CIN VIN LM3488 Figure 35. Reducing IC Input Noise 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.
PAGE 23
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 Figure 36. Typical SEPIC Converter POWER MOSFET SELECTION As in boost converter, the 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 24
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com (40) (41) maintains the condition IL > ΔiL/2 to ensure constant current mode. (VIN - VQ)(1-D) L1 > 2IOUTfS L2 > (42) (VIN - VQ)D 2IOUTfS (43) Peak current in the inductor, to ensure the inductor does not saturate: (44) (45) IL1PK must be lower than the maximum current rating set by the current sense resistor. The value of L1 can be increased above the minimum recommended to reduce input ripple and output ripple.
PAGE 25
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 (49) Where (50) is the ripple voltage across the SEPIC capacitor, and (51) is the ripple current through the inductor L1. The energy balance equation can be solved to provide a minimum value for CS: (52) 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.
PAGE 26
LM3488 LM3488-Q1 SNVS089M – JULY 2000 – REVISED MARCH 2013 www.ti.com Other Application Circuits VIN = 3.3V (±10%) + CIN 100 PF, 6.3V L 10 PH ISEN VIN CC 22 nF COMP RC 4.7k D MBRD340 RFA 20k FA/SD/SYNC FB + COUT 40k LM3488 100 PF, 10V x2 Q1 IRF7807 DR RF1 AGND VOUT = 5V, 2A 60k RF2 PGND CSN 0.01 PF RSN 0.025: Figure 37.
PAGE 27
LM3488 LM3488-Q1 www.ti.com SNVS089M – JULY 2000 – REVISED MARCH 2013 REVISION HISTORY Changes from Revision L (March 2013) to Revision M • Page Changed layout of National Data Sheet to TI format ..........................................................................................................
PAGE 28
PACKAGE OPTION ADDENDUM www.ti.
PAGE 29
PACKAGE OPTION ADDENDUM www.ti.com 1-Nov-2013 (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided.
PAGE 30
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 LM3488MM VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3488MM/NOPB VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3488MMX VSSOP DGK 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.
PAGE 31
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) LM3488MM VSSOP DGK 8 1000 210.0 185.0 35.0 LM3488MM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM3488MMX VSSOP DGK 8 3500 367.0 367.0 35.0 LM3488MMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0 LM3488QMM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM3488QMMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.
PAGE 32
PAGE 33
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.