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LTC3115-2

31152f

For more information www.linear.com/LTC3115-2

Typical applicaTion

FeaTures DescripTion

40V, 2A Synchronous

Buck-Boost DC/DC Converter

The LTC

3115-2 is a high voltage monolithic synchronous

buck-boost DC/DC converter optimized for applications

subject to fast (<1ms) input voltage transients. For all other

applications, the LTC3115-1 is recommended. With its wide

2.7V to 40V input and output voltage ranges, the LTC3115-2

is well suited for use in a wide variety of automotive and

industrial power supplies. A proprietary low noise switch

ing algorithm optimizes efficiency with input voltages that

are above, below or even equal to the output voltage and

ensures seamless transitions between operational modes.

Programmable frequency PWM mode operation provides

low noise, high efficiency operation and the ability to syn

chronize switching to an external clock. Switching frequen-

cies up to 2MHz are supported to allow use of small value in-

ductors for miniaturization of the application circuit. Pin se-

lectable Burst Mode operation reduces standby current and

improves light load efficiency which, combined with a 3µA

shutdown current, make the LTC3115-2 ideally suited for

battery-powered applications. Additional features include

output disconnect in shutdown, short-circuit protection

and internal soft-start. The LTC3115-2 is available in ther

mally enhanced 16-lead 4mm × 5mm × 0.75mm DFN and

20-lead TSSOP packages.

Efficiency vs V

applicaTions

Wide V

Range: 2.7V to 40V

Wide V

OUT

Range: 2.7V to 40V

0.8A Output Current for V

≥ 3.6V, V

OUT

= 5V

2A Output Current in Step-Down Operation

for V

≥ 6V

Programmable Frequency: 100kHz to 2MHz

Synchronizable Up to 2MHz with an External Clock

Up to 95% Efficiency

30µA No-Load Quiescent Current in Burst Mode

Operation

Ultralow Noise Buck-Boost PWM

Internal Soft-Start

3µA Supply Current in Shutdown

Programmable Input Undervoltage Lockout

Small 4mm × 5mm × 0.75mm DFN Package

Thermally Enhanced 20-Lead TSSOP Package

24V/28V Industrial Applications

Automotive Power Systems

Telecom, Servers and Networking Equipment

FireWire Regulator

Multiple Power Source Supplies

L, LT, LTC, LTM, Burst Mode, LTspice, Linear Technology and the Linear logo are registered

trademarks and No R

SENSE

is a trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Protected by U.S. Patents including

6404251, 6166527 and others pending.

BST1 BST2

OUT

PWM/SYNC

FBRUN

SW1 SW2

GND PGND

LTC3115-2

10µH

5V, 750kHz Wide Input Voltage Range Buck-Boost Regulator

0.1µF

BURST PWM

2.7V TO

40V

0.1µF

33pF

(OPTIONAL)

0.8A V

> 3.6V

2A V

≥ 6V

4.7µF 47µF × 2

249k

4.7µF

31152 TA01a

47.5k

15k

137k

3300pF

OFF ON

INPUT VOLTAGE (V)

EFFICIENCY (%)

31152 TA01b

2 10

LOAD

= 0.5A

LOAD

= 1A

OUT

= 5V

Summary of content (40 pages)

PAGE 1
LTC3115-2 40V, 2A Synchronous Buck-Boost DC/DC Converter Features n n n n n n n n n n n n n n Description Wide VIN Range: 2.7V to 40V Wide VOUT Range: 2.7V to 40V 0.8A Output Current for VIN ≥ 3.
PAGE 2
LTC3115-2 Absolute Maximum Ratings (Note 1) VIN, PVIN, PVOUT......................................... –0.3V to 45V VSW1 DC............................................ –0.3V to (PVIN + 0.3V) Pulsed (<100ns).......................–1.5V to (PVIN + 1.5V) VSW2 DC..........................................–0.3V to (PVOUT + 0.3V) Pulsed (<100ns)..................... –1.5V to (PVOUT + 1.5V) VRUN.............................................. –0.3V to (VIN + 0.3V) VBST1......................................VSW1 – 0.
PAGE 3
LTC3115-2 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). PVIN = VIN = 24V, PVOUT = 5V, unless otherwise noted.
PAGE 4
LTC3115-2 Electrical Characteristics operating lifetime; operating lifetime is derated for junction temperatures greater than 125°C. The maximum ambient temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors.
PAGE 5
LTC3115-2 Typical Performance Characteristics Burst Mode Efficiency, VOUT = 12V, L = 15µH Burst Mode Efficiency, VOUT = 24V, L = 15µH 90 95 90 85 90 85 80 85 75 70 65 60 VIN = 3.6V VIN = 12V VIN = 24V VIN = 36V 55 50 0.1 1 10 LOAD CURRENT (mA) 80 80 EFFICIENCY (%) EFFICIENCY (%) EFFICIENCY (%) Burst Mode Efficiency, VOUT = 5V, L = 15µH, Non-Bootstrapped 75 70 65 55 50 0.1 100 INPUT CURRENT (µA) 250 200 150 100 50 1 10 LOAD CURRENT (mA) fSW = 1MHz 45 50 0.
PAGE 6
LTC3115-2 Typical Performance Characteristics NON-BOOTSTRAPPED 75 70 16 30 14 25 VIN = 36V VOUT = 24V 20 VIN = 12V VOUT = 5V 15 10 0 1000 500 1500 SWITCHING FREQUENCY (kHz) 0 2000 11.7 11.6 11.5 11.4 11.3 11.2 11.1 11.0 –50 0 50 100 TEMPERATURE (°C) CHANGE IN VOLTAGE FROM ZERO LOAD (%) VCC/PVCC CURRENT (mA) 11.8 150 0 500 1000 4 0.5 0.4 0.3 0.2 0.1 0 –0.2 –0.4 –0.6 –0.8 –1.0 –50 0 50 100 TEMPERATURE (°C) 150 31152 G20 5.5 Output Voltage Line Regulation 0.5 0.4 0.3 0.2 0.
PAGE 7
LTC3115-2 Typical Performance Characteristics (TA = 25°C unless otherwise specified) VCC Regulator Dropout Voltage vs Temperature 0.25 1.0 VIN = 4V IVCC = 20mA 2.0 0.8 1.5 CHANGE FROM 25°C (%) 0.15 0.10 0.05 1.0 CHANGE FROM 25°C (%) 0.6 0.20 DROPOUT VOLTAGE (V) RUN Pin Hysteresis Current vs Temperature RUN Pin Threshold vs Temperature 0.4 0.2 0 –0.2 –0.4 0.5 0 –0.5 –1.0 –0.6 –1.5 –0.8 0 –50 0 50 100 TEMPERATURE (°C) –1.0 –50 150 0 50 100 TEMPERATURE (°C) –2.0 –50 150 10000 2.
PAGE 8
LTC3115-2 Typical Performance Characteristics Power Switch Resistance vs VCC 165 1.0 5 0.8 4 0.6 160 155 150 145 2.5 3.5 3 4 VCC (V) 4.5 5 5.5 3 CHANGE FROM 25°C (%) CHANGE FROM 25°C (%) POWER SWITCH (A-D) RESISTANCE (mΩ) Inductor Current Limit Thresholds vs Temperature FB Voltage vs Temperature 170 140 (TA = 25°C unless otherwise specified) 0.4 0.2 0 –0.2 –0.4 –0.
PAGE 9
LTC3115-2 Typical Performance Characteristics (TA = 25°C unless otherwise specified) DIE TEMPERATURE CHANGE FROM AMBIENT (°C) Die Temperature Rise vs Load Current, VOUT = 12V, fSW = 750kHz 80 Load Transient (0A to 1A), VIN = 24V, VOUT = 5V VIN = 36V VIN = 24V VIN = 12V VIN = 6V 70 60 Load Transient (0A to 0.8A), VIN = 3.
PAGE 10
LTC3115-2 Pin Functions (DHD/FE) RUN (Pin 1/Pin 2): Input to Enable and Disable the IC and Set Custom Input UVLO Thresholds. The RUN pin can be driven by an external logic signal to enable and disable the IC. In addition, the voltage on this pin can be set by a resistor divider connected to the input voltage in order to provide an accurate undervoltage lockout threshold. The IC is enabled if RUN exceeds 1.21V nominally. Once enabled, a 0.5µA current is sourced by the RUN pin to provide hysteresis.
PAGE 11
LTC3115-2 Pin Functions (DHD/FE) PWM/SYNC (Pin 16/Pin 19): Burst Mode/PWM Mode Control Pin and Synchronization Input. Forcing this pin high causes the IC to operate in fixed frequency PWM mode at all loads using the internal oscillator at the frequency set by the RT Pin. Forcing this pin low places the IC into Burst Mode operation regardless of load current. Burst Mode operation inproves light load efficiency and reduces standby current.
PAGE 12
LTC3115-2 Operation INTRODUCTION The LTC3115-2 is a monolithic buck-boost converter that can operate with input and output voltages from as low as 2.7V to as high as 40V. Four internal low resistance Nchannel DMOS switches minimize the size of the application circuit and reduce power losses to maximize efficiency. Internal high side gate drivers, which require only the addition of two small external capacitors, further simplify the design process.
PAGE 13
LTC3115-2 Operation Oscillator and Phase-Locked Loop VOUT The LTC3115-2 operates from an internal oscillator with a switching frequency that is configured by a single external resistor between the RT pin and ground. For noise sensitive applications, an internal phase-locked loop allows the LTC3115-2 to be synchronized to an external clock signal applied to the PWM/SYNC pin. The phase-locked loop is only able to increase the frequency of the internal oscillator to obtain synchronization.
PAGE 14
LTC3115-2 Operation of this current limit circuit is limited by the dynamics of the error amplifier. On a hard output short, it is possible for the inductor current to increase substantially beyond the current limit threshold before the average current limit has time to react and reduce the inductor current. For this reason, there is a second current limit circuit which turns off power switch A if the current through switch A exceeds approximately 160% of the primary inductor current limit threshold.
PAGE 15
LTC3115-2 Operation SOFT-START To minimize input current transients on power-up, the LTC3115-2 incorporates an internal soft-start circuit with a nominal duration of 9ms. The soft-start is implemented by a linearly increasing ramp of the error amplifier reference voltage during the soft-start duration. As a result, the duration of the soft-start period is largely unaffected by the size of the output capacitor or the output regulation voltage.
PAGE 16
LTC3115-2 Operation threshold. Therefore, in order to place the part in shutdown and reduce the input current to its minimum level (3µA typical) it is necessary to ensure that the RUN pin is brought below the worst-case logic threshold (0.3V). The RUN pin is a high voltage input and can be connected directly to VIN to continuously enable the part when the input supply is present.
PAGE 17
LTC3115-2 Applications Information The standard LTC3115-2 application circuit is shown as the typical application on the front page of this data sheet. The appropriate selection of external components is dependent upon the required performance of the IC in each particular application given considerations and trade-offs such as PCB area, cost, output and input voltage, allowable ripple voltage, efficiency and thermal considerations.
PAGE 18
LTC3115-2 Applications Information provides a small sampling of inductors that are well suited to many LTC3115-2 applications. In applications with VOUT ≥ 20V, it is recommended that a minimum inductance value, LMIN, be utilized where f is the switching frequency: LMIN = 12H ( f / Hz ) ∆VP-P(BUCK) = VALUE DCR MAX DC (µH) (mΩ) CURRENT (A) ILOADtLOW COUT ∆VP-P(BOOST) = Table 1.
PAGE 19
LTC3115-2 Applications Information may be necessary to add an additional small value bypass capacitor near the VIN pin. When powered through long leads or from a high ESR power source, a larger value bulk input capacitor may be required. In such applications, a 47µF to 100µF electrolytic capacitor in parallel with a 1µF ceramic capacitor generally yields a high performance, low cost solution.
PAGE 20
LTC3115-2 Applications Information Programming Custom Input UVLO Thresholds With the addition of an external resistor divider connected to the input voltage as shown in Figure 4, the RUN pin can be used to program the input voltage at which the LTC3115-2 is enabled and disabled. For a rising input voltage, the LTC3115-2 is enabled when VIN reaches the threshold given by the following equation, where R1 and R2 are the values of the resistor divider resistors: to 2MΩ).
PAGE 21
LTC3115-2 Applications Information A significant performance advantage can be attained in applications which have the converter output voltage programmed to 5V if the output voltage is utilized to power the PVCC and VCC rails. This can be done by connecting a Schottky diode from VOUT to PVCC/VCC as shown in Figure 6. With this bootstrap diode installed, the gate driver currents are generated directly by the buck-boost converter at high efficiency rather than through the internal linear regulator.
PAGE 22
LTC3115-2 Applications Information The denominator of the buck mode transfer function exhibits a pair of resonant poles generated by the LC filtering of the power stage.
PAGE 23
LTC3115-2 Applications Information Compensation of the Voltage Loop VOUT The small-signal models of the LTC3115-2 reveal that the transfer function from the error amplifier output, VC, to the output voltage is characterized by a set of resonant poles and a possible zero generated by the ESR of the output capacitor as shown in the Bode plot of Figure 7. In boost mode operation, there is an additional right half plane zero that produces phase lag and increasing gain at higher frequencies.
PAGE 24
LTC3115-2 Applications Information In most applications the compensation network is designed so that the loop crossover frequency is above the resonant frequency of the power stage, but sufficiently below the boost mode right half plane zero to minimize the additional phase loss. Once the crossover frequency is decided upon, the phase boost provided by the compensation network is centered at that point in order to maximize the phase margin.
PAGE 25
LTC3115-2 Applications Information Loop Compensation Example This section provides an example illustrating the design of a compensation network for a typical LTC3115-2 application circuit. In this example a 5V regulated output voltage is generated with the ability to supply a 500mA load from an input power source ranging from 3.5V to 30V. To reduce switching losses a 750kHz switching frequency has been chosen for this example.
PAGE 26
LTC3115-2 Applications Information 50 40 –80 PHASE 20 –120 10 –160 0 –200 –10 –240 –20 10 –280 fC 100 1k 10k FREQUENCY (Hz) PHASE (DEG) GAIN (dB) –40 GAIN 30 –30 the compensated error amplifier is determined simply by the amount of separation between the poles and zeros as shown by the following equation: 0 100k –320 1M 31152 F12 Figure 12. Converter Bode Plot, VIN = 3.
PAGE 27
LTC3115-2 Applications Information ⎡ ⎤ 50 GCENTER = 20log ⎢ ⎥ dB ⎣ 2πfC R TOP CFB ⎦ This equation completes the set of constraints needed to determine the compensation component values. Specifically, the two zeros, fZERO1 and fZERO2, should be located near 3.43kHz. The two poles, fPOLE2 and fPOLE3, should be located near 168kHz and the gain should be set to provide a gain at the crossover frequency of GCENTER = –19dB.
PAGE 28
LTC3115-2 Applications Information The final step in the design process is to compute the Bode plot for the entire loop using the designed compensation network and confirm its phase margin and crossover frequency. The complete loop Bode plot for this example is shown in Figure 14. The loop crossover frequency is 22kHz which is close to the design target and the phase margin is approximately 60°.
PAGE 29
LTC3115-2 Applications Information PCB Layout Considerations The LTC3115-2 buck-boost converter switches large currents at high frequencies. Special attention should be paid to the PC board layout to ensure a stable, noise-free and efficient application circuit. Figures 16 and 17 show a representative PCB layout for each package option to outline some of the primary considerations. A few key guidelines are provided below: 1.
PAGE 30
LTC3115-2 Applications Information VIA TO GROUND PLANE (AND TO INNER LAYER WHERE SHOWN) [16] PWM/ SYNC [1] RUN [2] SW2 VOUT KELVIN BACK TO GND PIN RBOT RT [17] PGND [15] SW1 VIN [3] PVOUT [14] PVIN [4] GND [13] BST1 CBST1 CBST2 [5] GND [12] BST2 [6] VC [11] PVCC [7] FB [10] VIN [8] RT [9] VCC INNER PCB LAYER ROUTES RTOP KELVIN TO VOUT 31152 F15 UNINTERRUPTED GROUND PLANE SHOULD EXIST UNDER ALL COMPONENTS SHOWN IN BOLD AND UNDER TRACES CONNECTING TO THOSE COMPONENTS Figure 16.
PAGE 31
LTC3115-2 Applications Information VIA TO GROUND PLANE (AND TO INNER LAYER WHERE SHOWN) [1] PGND [20] PGND [2] RUN [19] PWM/ SYNC [3] SW2 VOUT KELVIN BACK TO GND PIN RBOT RT [21] PGND [18] SW1 VIN [4] PVOUT [17] PVIN [5] GND [16] BST1 CBST1 CBST2 [6] GND [15] BST2 [7] VC [14] PVCC [8] FB [13] VIN [9] RT [12] VCC [10] PGND [11] PGND INNER PCB LAYER ROUTES RTOP KELVIN TO VOUT 31152 F17 UNINTERRUPTED GROUND PLANE SHOULD EXIST UNDER ALL COMPONENTS SHOWN IN BOLD AND UNDER TRACES CONNE
PAGE 32
LTC3115-2 Typical Applications Automotive 450kHz Regulator with 100k Maximum Resistor Value L1 10µH CBST1 0.1µF CBST2 0.1µF BST1 SW1 2.7V TO 40V SW2 BST2 PVIN VIN CIN 10µF PVOUT RUN LTC3115-2 VC CO 47µF × 2 CFB RFB 33nF 13.7k RTOP 100k CFF 330pF 5V 1A VIN > 4V 2A VIN ≥ 6V RFF 1.5k 100k FB PWM/SYNC PVCC VCC RT RT 80.6k GND PGND CIN: AVX22205C106KAT2A CO: GRM43ER61A476KE19L L1: WÜRTH 744 778910 1000pF RBOT 24.9k C1 4.7µF 31152 TA02a Fast (10µs) Line Transient from VIN = 13.
PAGE 33
LTC3115-2 Typical Applications Wide Input Voltage Range (10V to 40V) 1MHz 24V Supply at 400mA L1 15µH CBST2 0.1µF CBST1 0.1µF BST1 SW1 10V TO 40V UVLO PROGRAMMED TO 10V (1.3V HYSTERESIS) R1 953k SW2 BST2 PVIN VIN CIN 4.7µF RUN PVOUT LTC3115-2 R2 130k VC CO 10µF CFB RFB 4700pF 4.99k FB RT 35.7k GND 31152 TA03a Efficiency vs VIN Maximum Load Current vs VIN 92 2.5 90 EFFICIENCY (%) 2.0 LOAD CURRENT (A) RFF 4.99k C1 4.7µF PGND L1: WÜRTH 744 066 150 1.5 1.0 0.5 0 CFF 47pF RBOT 43.
PAGE 34
LTC3115-2 Typical Applications Industrial 12V 1MHz Regulator with 10.6V Input Undervoltage Lockout Threshold L1 10µH CBST2 0.1µF CBST1 0.1µF BST1 SW1 10V TO 40V ENABLED WHEN VIN REACHES 10.6V DISABLED WHEN VIN FALLS BELOW 8.7V CIN 10µF R1 2M SW2 BST2 PVIN VIN PVOUT LTC3115-2 VC RUN R2 255k RT 35.7k CFB RFB 820pF 40.2k FB PWM/SYNC PVCC VCC RT GND 12V 1.4A CO 22µF RTOP 1M CFF 33pF RFF 10k RBOT 90.9k C1 4.
PAGE 35
LTC3115-2 Typical Applications 24V 750kHz Industrial Power Rail from 20V to 40V Input L1 22µH * CBST1 0.1µF BST1 SW1 20V TO 40V OPEN DRAIN OUTPUT R1 500k SW2 BST2 PVIN VIN CIN 10µF *OPTIONAL: INSTALL IN APPLICATIONS SUBJECT TO OUTPUT OVERLOAD OR SHORT-CIRCUIT CONDITIONS CBST2 0.1µF RUN PVOUT 1µF LTC3115-2 ON OFF VC + RFB 25k CO 82µF CFB 3300pF GND PGND CFF 100pF RTOP 1M RFF 51k 100pF FB RT PWM/SYNC PVCC VCC 24V 1.5A RT 47.5k RBOT 43.2k C1 4.
PAGE 36
LTC3115-2 Typical Applications USB, FireWire, Automotive and Unregulated Wall Adapter to Regulated 5V (750kHz) USB 4.1V TO 5.5V FireWire 8V TO 36V AUTOMOTIVE 3.6V TO 40V WALL ADAPTER 4V TO 40V D1 D2 L1 10µH CBST1 0.1µF D3 D4 CBST2 0.1µF BST1 SW1 + 2.2µF 100µF ELECT SW2 BST2 PVIN VIN PVOUT LTC3115-2 PWM/SYNC BURST PWM VC RUN OFF ON CO 47µF ×2 CFB RFB 4700pF 100k FB RT 47.5k PVCC VCC RT GND PGND 5V 600mA RTOP 1M CFF 47pF RFF 51k RBOT 249k C1 4.
PAGE 37
LTC3115-2 Typical Applications 1.5MHz, 12V Regulator with 8V to 40V Input Voltage Range L1 4.7µH CBST2 0.1µF CBST1 0.1µF BST1 SW1 8V TO 40V CI 4.7µF SW2 BST2 PVIN VIN PVOUT RUN LTC3115-2 PWM/SYNC BURST PWM RT 23.7k VC CO 22µF CFB RFB 1000pF 15k RTOP 1M PVCC VCC GND PGND CFF 33pF RFF 15k FB RT 12V AT 500mA 1A VIN > 10V RBOT 90.9k C1 4.
PAGE 38
LTC3115-2 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DHD Package 16-Lead Plastic DFN (5mm × 4mm) (Reference LTC DWG # 05-08-1707) 0.70 ±0.05 4.50 ±0.05 3.10 ±0.05 2.44 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 4.34 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 5.00 ±0.10 (2 SIDES) R = 0.20 TYP 4.00 ±0.10 (2 SIDES) 9 R = 0.115 TYP 0.40 ± 0.10 16 2.44 ± 0.
PAGE 39
LTC3115-2 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev J) Exposed Pad Variation CA 6.40 – 6.60* (.252 – .260) 4.95 (.195) 4.95 (.195) 20 1918 17 16 15 14 13 12 11 6.60 ±0.10 4.50 ±0.10 2.74 (.108) 6.40 2.74 (.252) (.108) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 9 10 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.
PAGE 40
LTC3115-2 Typical Application 2MHz Automotive 5V Regulator with Cold Crank Capability L1 3.3µH CBST2 0.1µF CBST1 0.1µF BST1 SW1 AUTOMOTIVE 4V TO 40V SW2 BST2 PVIN VIN CIN 4.7µF PVOUT LTC3115-2 PWM/SYNC BURST PWM VC RUN OFF ON CO 47µF × 2 CFB RFB 4700pF 24.3k 5V 800mA RTOP 100k CFF 100pF RFF 2k 100k FB CO: MURATA GRM43ER61A476 L1: COILCRAFT LPS5030-332ML RT 17.8k 1000pF RBOT 24.9k PVCC RT GND VCC PGND C1 4.