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LTC3780

Rev G

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TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

High Efficiency, Synchronous,

4-Switch Buck-Boost Controller

The LTC

3780 is a high performance buck-boost switch-

ing regulator controller that operates from input voltages

above, below

or equal to the output voltage. The constant

frequency current mode architecture allows a phase-

lockable frequency of up to 400kHz. With a wide 4V to

30V (36V maximum) input and output range and seamless

transfers between operating modes, the LTC3780 is ideal

for automotive, telecom and battery-powered systems.

The operating mode of the controller is determined through

the FCB pin. For boost operation, the FCB mode pin can

select among Burst Mode

operation, discontinuous mode

and forced continuous mode. During buck operation, the

FCB mode pin can select among skip-cycle mode, discon

tinuous mode and forced continuous mode. Burst Mode

operation and skip-cycle mode provide high efficiency

operation at light loads while forced continuous mode

and discontinuous mode operate at a constant frequency.

Fault protection is provided by an output overvoltage

comparator and internal foldback current limiting. A power

good output pin indicates when the output is within 7.5%

of its designed set point.

High Efficiency Buck-Boost Converter

Single Inductor Architecture Allows V

Above,

Below or Equal to V

OUT

Wide V

Range: 4V to 36V Operation

Synchronous Rectification: Up to 98% Efficiency

Current Mode Control

±1% Output Voltage Accuracy: 0.8V < V

OUT

< 30V

Phase-Lockable Fixed Frequency: 200kHz to 400kHz

Power Good Output Voltage Monitor

Internal LDO for MOSFET Supply

Quad N-Channel MOSFET Synchronous Drive

OUT

Disconnected from V

During Shutdown

Adjustable Soft-Start Current Ramping

Foldback Output Current Limiting

Selectable Low Current Modes

Output Overvoltage Protection

Available in 24-Lead SSOP and Exposed Pad

(5mm × 5mm) 32-Lead QFN Packages

Automotive Systems

Telecom Systems

DC Power Distribution Systems

High Power Battery-Operated Devices

Industrial Control

TG2

0.1µF 0.1µF

BOOST2

SW2

BG2

TG1

BOOST1

SW1

BG1

PLLIN

RUN

OSENSE

SGND FCB

0.010Ω

4.7µF

2200pF

1µF

CER

100µF

16V

CER

330µF

16V

ON/OFF

0.1µF

4.7µH

20k

PGOOD

LTC3780

INTV

SENSE

–

PGND

7.5k

3780 TA01

105k

22µF

50V

CER

5V TO 32V

OUT

12V

(V)

EFFICIENCY (%)

POWER LOSS (W)

100

15 25

3780 TA01b

5 10

20 30 35

Efficiency and Power Loss

OUT

= 12V, I

LOAD

= 5A

All registered trademarks and trademarks are the property of their respective owners. Protected

by U.S. Patents, including 5481178, 6304066, 5929620, 5408150, 6580258, patent pending on

current mode architecture and protection.

Downloaded from Arrow.com.

Summary of content (30 pages)

PAGE 1
LTC3780 High Efficiency, Synchronous, 4-Switch Buck-Boost Controller FEATURES n n n n n n n n n n n n n n n DESCRIPTION Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT Wide VIN Range: 4V to 36V Operation Synchronous Rectification: Up to 98% Efficiency Current Mode Control ±1% Output Voltage Accuracy: 0.
PAGE 2
LTC3780 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (VIN)......................... –0.3V to 36V Topside Driver Voltages (BOOST1, BOOST2)................................... –0.3V to 42V Switch Voltage (SW1, SW2).......................... –5V to 36V INTVCC, EXTVCC, (BOOST – SW1), (BOOST2 – SW2), PGOOD........................... –0.3V to 7V RUN, SS........................................................ –0.3V to 6V PLLIN Voltage........................................... –0.3V to 5.
PAGE 3
LTC3780 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3780EG#PBF LTC3780EG#TRPBF LTC3780EG 24-Lead Plastic SSOP –40°C to 85°C LTC3780IG#PBF LTC3780IG#TRPBF LTC3780IG 24-Lead Plastic SSOP –40°C to 125°C LTC3780MPG#PBF LTC3780MPG#TRPBF LTC3780MPG 24-Lead Plastic SSOP –55°C to 125°C LTC3780EUH#PBF LTC3780EUH#TRPBF 3780 32-Lead (5mm × 5mm) Plastic QFN –40°C to 85°C LTC3780IUH#PBF LTC3780IUH#TRPBF 3780I 32-Lead (5mm × 5mm) Plast
PAGE 4
LTC3780 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. (Note 7) VIN = 15V unless otherwise noted.
PAGE 5
LTC3780 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. (Note 7) VIN = 15V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX ∆VFBH PGOOD Upper Threshold VOSENSE Rising 5.5 7.5 10 –5.5 –7.5 –10 UNITS PGOOD Output ∆VFBL PGOOD Lower Threshold VOSENSE Falling ∆VFB(HYST) PGOOD Hysteresis VOSENSE Returning 2.5 VPGL PGOOD Low Voltage IPGOOD = 2mA 0.
PAGE 6
LTC3780 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Output Current (Boost Operation) 100 TA = 25°C, unless otherwise noted. Efficiency vs Output Current (Buck Operation) Efficiency vs Output Current 100 BURST 100 BURST 90 90 90 DCM SC 70 CCM 60 50 0.1 1 DCM 70 CCM 60 50 VIN = 6V VOUT = 12V 40 0.01 80 0.1 1 Supply Current vs Input Voltage INTVCC VOLTAGE (V) SUPPLY CURRENT (µA) STANDBY 1000 500 SHUTDOWN 30 6.0 100 5.5 5.0 4.5 3.
PAGE 7
LTC3780 TYPICAL PERFORMANCE CHARACTERISTICS Continuous Current Mode (CCM, VIN = 6V, VOUT = 12V) Continuous Current Mode (CCM, VIN = 12V, VOUT = 12V) SW2 10V/DIV SW2 10V/DIV SW1 10V/DIV SW1 10V/DIV VOUT 100mV/DIV IL 2A/DIV VIN = 6V VOUT = 12V 5µs/DIV TA = 25°C, unless otherwise noted.
PAGE 8
LTC3780 TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency vs Temperature Undervoltage Reset vs Temperature Minimum Current Sense Threshold vs Duty Factor (Buck) 4.2 450 VPLLFLTR = 2.4V 4.0 UNDERVOLTAGE RESET (V) 350 VPLLFLTR = 1.2V 300 250 VPLLFLTR = 0V 200 –20 150 100 3.8 ISENSE+ (mV) 400 FREQUENCY (kHz) TA = 25°C, unless otherwise noted. 3.6 3.4 –60 3.2 50 0 –75 –50 –25 0 25 50 75 TEMPERATURE (°C) 3.
PAGE 9
LTC3780 TYPICAL PERFORMANCE CHARACTERISTICS Load Step TA = 25°C, unless otherwise noted.
PAGE 10
LTC3780 PIN FUNCTIONS (SSOP/QFN) PGOOD (Pin 1/Pin 30): Open-Drain Logic Output. PGOOD is pulled to ground when the output voltage is not within ±7.5% of the regulation point. operation. When the pin is tied to INTVCC, the constant frequency discontinuous current mode is active in buck or boost operation. SS (Pin 2/Pin 31): Soft-start reduces the input power sources’ surge currents by gradually increasing the controller’s current limit. A minimum value of 6.8nF is recommended on this pin.
PAGE 11
LTC3780 PIN FUNCTIONS (SSOP/QFN) BG2, BG1 (Pins 16, 18/Pins 18, 20): Bottom Gate Drive. Drives the gate of the bottom N-channel MOSFET between ground and INTVCC. PGND (Pin 17/Pin 19): Power Ground. Connect this pin closely to the source of the bottom N-channel MOSFET, the (–) terminal of CVCC and the (–) terminal of CIN (Figure 11). INTVCC (Pin 19/Pin 21): Internal 6V Regulator Output. The driver and control circuits are powered from this voltage. Bypass this pin to ground with a minimum of 4.
PAGE 12
LTC3780 BLOCK DIAGRAM INTVCC VIN BOOST2 STBYMD FCB + TG2 FCB ILIM BUCK LOGIC SW2 INTVCC – + BG2 RSENSE PGND IREV BG1 – FCB BOOST LOGIC 1.2V 4(VFB) + 1.2µA SS INTVCC SW1 TG1 ICMP BOOST1 OV – – 0.86V INTVCC + RUN SLOPE EA 100k VOSENSE – + VOUT VFB 0.80V ITH SHDN RST 4(VFB) RUN/ SS SENSE+ SENSE– VREF VIN + – EXTVCC 6V FIN PLLFLTR 6V LDO REG CLK 0.86V INTVCC SGND PLLIN 50k 5.7V + PHASE DET VIN RLP OSCILLATOR CLP – + PGOOD INTERNAL SUPPLY VOSENSE – 0.
PAGE 13
LTC3780 OPERATION MAIN CONTROL LOOP VOUT VIN The LTC3780 is a current mode controller that provides an output voltage above, equal to or below the input voltage. The LTC proprietary topology and control architecture employs a current-sensing resistor in buck or boost modes. The sensed inductor current is controlled by the voltage on the ITH pin, which is the output of the amplifier EA. The VOSENSE pin receives the voltage feedback signal, which is compared to the internal reference voltage by the EA.
PAGE 14
LTC3780 OPERATION of the cycle. switches C and D will alternate, behaving like a typical synchronous boost regulator. CLOCK SWITCH A SWITCH B 0V SWITCH C HIGH SWITCH D IL 3780 F03 Figure 3. Buck Mode (VIN > VOUT) The duty cycle of switch C decreases until the minimum duty cycle of the converter in boost mode reaches DMIN_BOOST, given by: DMIN_BOOST = DBUCK-BOOST where DBUCK-BOOST is the duty cycle of the buck-boost switch range: DBUCK-BOOST = (200ns • f) • 100% and f is the operating frequency in Hz.
PAGE 15
LTC3780 OPERATION recharge. In buck mode, synchronous switch D is always on. switch A and synchronous switch B are alternately turned on to maintain the output voltage independent of direction of inductor current. Every ten cycles, synchronous switch D is forced off for about 300ns to allow CB to recharge. This is the least efficient operating mode at light load, but may be desirable in certain applications. In this mode, the output can source or sink current.
PAGE 16
LTC3780 OPERATION FOLDBACK CURRENT SHORT-CIRCUIT PROTECTION AND CURRENT LIMIT Foldback current limiting is activated when the output voltage falls below 70% of its nominal level, reducing power waste. During start-up, foldback current limiting is disabled. Switch A on-time is limited by output voltage. When output voltage is reduced and is lower than its nominal level, switch A on-time will be reduced.
PAGE 17
LTC3780 APPLICATIONS INFORMATION Figure 11 is a basic LTC3780 application circuit. External component selection is driven by the load requirement, and begins with the selection of RSENSE and the inductor value. Next, the power MOSFETs are selected. Finally, CIN and COUT are selected. This circuit can be configured for operation up to an input voltage of 36V. Selection of Operation Frequency The LTC3780 uses a constant frequency architecture and has an internal voltage controlled oscillator.
PAGE 18
LTC3780 APPLICATIONS INFORMATION where ∆IL is peak-to-peak inductor ripple current.
PAGE 19
LTC3780 APPLICATIONS INFORMATION Power MOSFET Selection and Efficiency Considerations The LTC3780 requires four external N-channel power MOSFETs, two for the top switches (switch A and D, shown in Figure 1) and two for the bottom switches (switch B and C shown in Figure 1). Important parameters for the power MOSFETs are the breakdown voltage VBR,DSS, threshold voltage VGS,TH, on-resistance RDS(ON), reverse transfer capacitance CRSS and maximum current IDS(MAX).
PAGE 20
LTC3780 APPLICATIONS INFORMATION Schottky Diode (D1, D2) Selection and Light Load Operation INTVCC Regulator The Schottky diodes D1 and D2 shown in Figure 13 conduct during the dead time between the conduction of the power MOSFET switches. They are intended to prevent the body diode of synchronous switches B and D from turning on and storing charge during the dead time.
PAGE 21
LTC3780 APPLICATIONS INFORMATION EXTVCC Connection The LTC3780 contains an internal P-channel MOSFET switch connected between the EXTVCC and INTVCC pins. When the voltage applied to EXTVCC rises above 5.7V, the internal regulator is turned off and a switch connects the EXTVCC pin to the INTVCC pin thereby supplying internal power. The switch remains closed as long as the voltage applied to EXTVCC remains above 5.5V. This allows the MOSFET driver and control power to be derived from the output when (5.
PAGE 22
LTC3780 APPLICATIONS INFORMATION The Standby Mode (STBYMD) Pin Function Fault Conditions: Overvoltage Protection The standby mode (STBYMD) pin provides several choices for start-up and standby operational modes. If the pin is pulled to ground, the SS pin is internally pulled to ground, preventing start-up and thereby providing a single control pin for turning off the controller.
PAGE 23
LTC3780 APPLICATIONS INFORMATION 3. INTVCC current. This is the sum of the MOSFET driver and control currents. This loss can be reduced by supplying INTVCC current through the EXTVCC pin from a high efficiency source, such as an output derived boost network or alternate supply if available. 4. CIN and COUT loss. The input capacitor has the difficult job of filtering the large RMS input current to the regulator in buck mode.
PAGE 24
LTC3780 APPLICATIONS INFORMATION Double-check the TJ in the MOSFET with 70°C ambient temperature: TJ = 70°C + 1.94W • 40°C/W = 147.6°C The maximum power dissipation of switch B occurs in buck mode. Assuming a junction temperature of TJ = 80°C with ρ80°C = 1.2, the power dissipation at VIN = 18V is: PB,BUCK = 18 – 12 18 • 5 2 • 1.2 • 0.009 = 90mW Double-check the TJ in the MOSFET at 70°C ambient temperature: TJ = 70°C + 0.09W • 40°C/W = 73.
PAGE 25
LTC3780 APPLICATIONS INFORMATION • Use immediate vias to connect the components (including the LTC3780’s SGND and PGND pins) to the ground plane. Use several large vias for each power component. • Use planes for VIN and VOUT to maintain good voltage filtering and to keep power losses low. • Flood all unused areas on all layers with copper. Flooding with copper will reduce the temperature rise of power components. Connect the copper areas to any DC net (VIN or GND). • Segregate the signal and power grounds.
PAGE 26
LTC3780 APPLICATIONS INFORMATION VOUT RPU 1 CSS 2 CC2 CC1 R1 C R RC R LTC3780 SENSE+ SENSE– 7 8 9 10 fIN SS 4 6 R2 PGOOD BOOST1 3 5 11 12 VPULLUP TG1 SW1 VIN ITH EXTVCC VOSENSE INTVCC SGND BG1 RUN PGND FCB BG2 PLLFLTR SW2 PLLIN TG2 STBYMD BOOST2 COUT CA 24 23 D DA 22 CF 21 D2 C 20 CVCC 19 L 18 RSENSE 17 16 B 15 D1 DB 14 CB 13 RIN A CIN 3780 F11 VIN Figure 11.
PAGE 27
LTC3780 PACKAGE DESCRIPTION G Package 24-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 7.90 – 8.50* (.311 – .335) 24 23 22 21 20 19 18 17 16 15 14 13 1.25 ±0.12 7.8 – 8.2 5.3 – 5.7 7.40 – 8.20 (.291 – .323) 0.42 ±0.03 0.65 BSC RECOMMENDED SOLDER PAD LAYOUT 1 2 3 4 5 6 7 8 9 10 11 12 5.00 – 5.60** (.197 – .221) 2.0 (.079) MAX 0° – 8° 0.09 – 0.25 (.0035 – .010) 0.65 (.0256) BSC 0.55 – 0.95 (.022 – .037) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2.
PAGE 28
LTC3780 PACKAGE DESCRIPTION UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693 Rev D) 0.70 ±0.05 5.50 ±0.05 4.10 ±0.05 3.50 REF (4 SIDES) 3.45 ± 0.05 3.45 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.75 ± 0.05 R = 0.05 TYP 0.00 – 0.05 R = 0.115 TYP PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 31 32 0.40 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 3.
PAGE 29
LTC3780 REVISION HISTORY (Revision history begins at Rev F) REV DATE DESCRIPTION F 4/13 Updated Note 7, fixed typos G 2/19 Added MP-Grade/Lead Free part number PAGE NUMBER 2, 3, 4, 5 3 Rev G Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice.
PAGE 30
LTC3780 TYPICAL APPLICATION RPU CSS 0.022µF 1 2 CC2 47pF CC1 0.01µF 68pF RC 100k R1 8.06k, 1% 3 4 5 6 R2 113k, 1% ON/OFF 7 8 9 10 VPULLUP PGOOD BOOST1 SS LTC3780 TG1 SENSE+ SW1 SENSE– VIN ITH EXTVCC VOSENSE INTVCC SGND BG1 RUN PGND FCB BG2 PLLFLTR SW2 PLLIN TG2 24 23 12 2V CSTBYMD 0.01µF STBYMD BOOST2 D Si7884DP DA BO540W 22 CF 0.1µF 21 C Si7884DP 20 CVCC 4.7µF 19 + D2 B320A COUT 330µF 16V L 4.