LTC3115-1 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 1A Output Current for VIN ≥ 3.
LTC3115-1 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.
LTC3115-1 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.
LTC3115-1 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.
LTC3115-1 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.
LTC3115-1 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 31151 G20 Downloaded from Arrow.com. 5.
LTC3115-1 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 –2.0 –50 150 50 100 TEMPERATURE (°C) 2.
LTC3115-1 Typical Performance Characteristics Power Switch Resistance vs VCC 160 155 150 3.5 4 VCC (V) 4.5 5 5.5 5 0.8 4 0.6 3 0.4 0.2 0 –0.2 –0.4 –0.6 145 3 1.0 CHANGE FROM 25°C (%) CHANGE FROM 25°C (%) POWER SWITCH (A-D) RESISTANCE (mΩ) 165 2.
LTC3115-1 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 VIN = 36V VIN = 24V VIN = 12V VIN = 6V 70 60 Load Transient (0A to 1A), VIN = 24V, VOUT = 5V VOUT (200mV/DIV) VOUT (200mV/DIV) INDUCTOR CURRENT (1A/DIV) INDUCTOR CURRENT (2A/DIV) 40 30 FRONT PAGE APPLICATION 20 0 LOAD CURRENT (1A/DIV) LOAD CURRENT (1A/DIV) 50 10 Load Transient (0A to 1A), VIN = 3.
LTC3115-1 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.
LTC3115-1 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 for improved efficiency at light load and reduced standby current.
LTC3115-1 Block Diagram Pin numbers are shown for the DHD package only. 14 15 2 3 SW2 SW1 PVIN A 10 PVOUT D B 3A –1.5A + – 0A + – C PGND PGND VIN CURRENT LIMIT + – REVERSE CURRENT LIMIT REVERSE BLOCKING LDO PVCC* ZERO CURRENT GATE DRIVES BST2 BST1 1.21V 1000mV 6 7 VC VIN FB 1000mV SOFT-START RAMP – + + ÷ 11 VCC BANDGAP REFERENCE PWM 13 VCC* + – INPUT UVLO 12 9 VIN 2.4V VIN 0.
LTC3115-1 Operation INTRODUCTION The LTC3115-1 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.
LTC3115-1 Operation duty cycle. The minimum switch low duration ensures that flying capacitor CBST1 is charged sufficiently to maintain the voltage on the BST1 rail. Oscillator and Phase-Locked Loop Error Amplifier and VIN Divider The LTC3115-1 has an internal high gain operational amplifier which provides frequency compensation of the control loop that maintains output voltage regulation.
LTC3115-1 Operation Reverse Current Limit Burst Mode OPERATION In PWM mode operation, the LTC3115-1 synchronously switches all four power devices. As a result, in addition to being able to supply current to the output, the converter has the ability to actively conduct current away from the output if that is necessary to maintain regulation. If the output is held above regulation, this could result in large reverse currents.
LTC3115-1 Operation VCC REGULATOR An internal low dropout regulator generates the 4.45V (nominal) VCC rail from VIN. The VCC rail powers the internal control circuitry and power device gate drivers of the LTC3115-1. The VCC regulator is disabled in shutdown to reduce quiescent current and is enabled by forcing the RUN pin above its logic threshold. The VCC regulator includes current limit protection to safeguard against short circuiting of the VCC rail.
LTC3115-1 Operation VIN THERMAL CONSIDERATIONS LTC3115-1 0.5µA VIN R1 RUN R2 0.8V 1.21V – + + – ENA ENABLE SWITCHING ENABLE VCC REGULATOR AND CONTROL CIRCUITS INPUT LOGIC THRESHOLD 31151 F03 Figure 3. Accurate RUN Pin Comparator input undervoltage lockout threshold. The buck-boost converter is enabled when the RUN pin reaches 1.21V which allows the rising UVLO threshold to be set via the resistor divider ratio.
LTC3115-1 Applications Information The standard LTC3115-1 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.
LTC3115-1 Applications Information provides a small sampling of inductors that are well suited to many LTC3115-1 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) ILOAD tLOW COUT ∆VP-P(BOOST) = Table 1.
LTC3115-1 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.
LTC3115-1 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 LTC3115-1 is enabled and disabled. For a rising input voltage, the LTC3115-1 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).
LTC3115-1 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.
LTC3115-1 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.
LTC3115-1 Applications Information Compensation of the Voltage Loop VOUT The small-signal models of the LTC3115-1 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.
LTC3115-1 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.
LTC3115-1 Applications Information Loop Compensation Example This section provides an example illustrating the design of a compensation network for a typical LTC3115-1 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.
LTC3115-1 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 31151 F12 Figure 12. Converter Bode Plot, VIN = 3.
LTC3115-1 Applications Information Assuming a multiple of 50 separation between the pole frequencies and zero frequencies this can be simplified to the following expression: 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.
LTC3115-1 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°.
LTC3115-1 Applications Information PCB Layout Considerations The LTC3115-1 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.
LTC3115-1 Applications Information VIA TO GROUND PLANE (AND TO INNER LAYER WHERE SHOWN) OPTIONAL SCHOTTKY DIODE [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 31151 F16 UNINTERRUPTED GROUND PLANE SHOULD EXIST UNDER ALL COMPONENTS SHOWN IN BOLD AND UNDER TRACES CONNECTING TO THOSE COMPO
LTC3115-1 Applications Information VIA TO GROUND PLANE (AND TO INNER LAYER WHERE SHOWN) OPTIONAL SCHOTTKY DIODE [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 31151 F17 UNINTERRUPTED GROUND PLANE SHOULD EXIST UNDER ALL COMPONENTS SHOWN IN BO
LTC3115-1 Typical Applications Wide Input Voltage Range (2.7V to 40V), High Efficiency 300kHz, Low Noise 5V Regulator L1 33µH CBST1 0.1µF CBST2 0.1µF BST1 SW1 2.7V TO 40V SW2 BST2 PVIN VIN CIN 10µF PVOUT RUN LTC3115-1 VC FB PWM/SYNC PVCC VCC RT RT 121k GND PGND + CO RTOP 330µF 1M CFB RFB 3300pF 93.1k CFF 82pF 5V 1A VIN > 3.6V 2A VIN ≥ 6V RFF 249k 27pF RBOT 249k D1 31151 TA02a C1 4.7µF CIN: MURATA GRM55DR61H106K CO: POSCAP 6TPB330M (7.3mm × 4.3mm × 2.
LTC3115-1 Typical Applications Wide Input Voltage Range (10V to 40V) 1MHz 24V Supply at 500mA L1 15µH CBST1 0.1µF CBST2 0.1µF BST1 SW1 10V TO 40V UVLO PROGRAMMED TO 10V (1.3V HYSTERESIS) R1 953k SW2 BST2 PVIN VIN CIN 10µF RUN PVOUT RTOP 1M CFB RFB 3300pF 10k LTC3115-1 R2 130k 24V 500mA CO 10µF VC RFF 10k FB RT 35.7k RBOT 43.2k PWM/SYNC PVCC VCC RT GND CFF 22pF C1 4.7µF PGND 31151 TA03a L1: WÜRTH 744 066 150 Maximum Load Current vs VIN Efficiency vs VIN 92 2.
LTC3115-1 Typical Applications Industrial 12V 1MHz Regulator with Custom Input Undervoltage Lockout Thresholds 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 LTC3115-1 VC RUN R2 255k RT 35.7k CO 22µF CFB RFB 820pF 40.2k FB PWM/SYNC PVCC VCC RT GND 12V 1.4A RTOP 1M CFF 33pF RFF 10k RBOT 90.9k C1 4.
LTC3115-1 Typical Applications 24V 750kHz Industrial Rail Restorer 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 RFB 25k LTC3115-1 ON OFF + VC CO 82µF CFB 3300pF CFF 47pF RTOP 1M RFF 51k 100pF FB RT PWM/SYNC PVCC VCC GND 24V 1.5A RT 47.5k RBOT 43.2k C1 4.
LTC3115-1 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 CBST2 0.1µF CBST1 0.1µF D3 D4 BST1 SW1 10µF SW2 BST2 PVIN VIN PVOUT LTC3115-1 PWM/SYNC BURST PWM VC RUN OFF ON CO 47µF ×2 CFB RFB 4700pF 100k FB RT 47.5k GND RTOP 1M CFF 47pF RFF 51k RBOT 249k PVCC VCC RT 5V 750mA C1 4.
LTC3115-1 Typical Applications Miniature Size 1.5MHz 12V Supply L1 4.7µH CBST2 0.1µF CBST1 0.1µF BST1 SW1 6V TO 40V CI 4.7µF SW2 BST2 PVIN VIN PVOUT RUN LTC3115-1 BURST PWM RT 23.7k PWM/SYNC VC RT FB CO 10µF CFB RFB 1000pF 15k RTOP 1M CFF 33pF RFF 15k RBOT 90.9k PVCC VCC GND 12V AT 500mA 1A VIN > 10V C1 4.
LTC3115-1 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.
LTC3115-1 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.
LTC3115-1 Revision History REV DATE DESCRIPTION A 4/13 Clarified Efficiency graph 1 Clarified Absolute Maximum Rating table, Package Drawing and Order Information 2 B 5/15 PAGE NUMBER Clarified Electrical Characteristics table 3 Clarified Pin Functions 11 Clarified Compensation formula 25 Clarified Figure 3 17 Clarified GBUCK formula 22 Clarified Loop Compensation Example 26 Clarified PCB Layout Considerations Added LTC3114-1 to Related Parts list 30, 31, 32 42 31151fb Information
LTC3115-1 Typical Application 750kHz Automotive 5V Regulator with Cold Crank Capability L1 6.8µH CBST2 0.1µF CBST1 0.1µF BST1 SW1 AUTOMOTIVE 3.6V TO 40V CIN 10µF SW2 BST2 PVIN VIN PVOUT LTC3115-1 PWM/SYNC BURST PWM VC RUN OFF ON CO 47µF CFB RFB 1000pF 54.9k FB CIN: MURATA GRM55DR61H106K CO: MURATA GRM43ER60J476K D1: PANASONIC MA785 L1: SUMIDA CDRH8D43HPNP RT 47.5k PVCC VCC RT GND PGND 5V 1A CFF 33pF RTOP 1M RFF 42.2k RBOT 249k D1* C1 4.
