Datasheet LTC7818 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | 40V, Low IQ, 3MHz, Triple Output Buck/Buck/Boost Synchronous Controller |
| Pages / Page | 44 / 1 — FEATURES. DESCRIPTION. Dual Buck Plus Single Boost Synchronous … |
| Revision | A |
| File Format / Size | PDF / 5.4 Mb |
| Document Language | English |
FEATURES. DESCRIPTION. Dual Buck Plus Single Boost Synchronous Controllers. Low Operating I. 14μA (14V to 3.3V, Channel 1 On)
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LTC7818 40V, Low IQ, 3MHz, Triple Output Buck/Buck/Boost Synchronous Controller
FEATURES DESCRIPTION
n
Dual Buck Plus Single Boost Synchronous Controllers
The LTC®7818 is a high performance triple output (buck/ n
Low Operating I
buck/boost) synchronous DC/DC switching regulator con-
Q:
n
14μA (14V to 3.3V, Channel 1 On)
troller that drives all N-channel power MOSFET stages. n
Outputs Remain in Regulation Through Cold Crank
Its constant-frequency current mode architecture allows a phase-lockable switching frequency of up to 3MHz.
Down to 1V Input Supply Voltage
n The LTC7818 operates from a wide 4.5V to 40V input
Wide Bias Input Voltage Range: 4.5V to 40V
n supply range. When biased from the output of the boost
Buck and Boost Output Voltages Up to 40V
n converter or another auxiliary supply, the LTC7818 can
Spread Spectrum Operation
operate from an input supply as low as 1V after start-up. n
RSENSE or DCR Current Sensing
n
Programmable Fixed Frequency (100kHz to 3MHz)
The LTC7818 synchronous boost PassThru capability n
PassThru™/100% Duty Cycle Capable for
minimizes losses in automotive start-stop applications.
Synchronous Boost MOSFET
The very low no-load quiescent current extends operating n run time in battery powered systems. OPTI-LOOP® com- Phase-Lockable Frequency (100kHz to 3MHz) n pensation allows the transient response to be optimized Selectable Continuous, Pulse-Skipping, or Low over a wide range of output capacitance and ESR values. Ripple Burst Mode Operation at Light Loads n The LTC7818 features a precision 0.8V reference for the Boost Channel Current Monitor Output bucks, 1.2V reference for the boost and a power good n Low Shutdown IQ: 1.5μA output indicator. n Small 40-Lead 6mm × 6mm QFN Package The LTC7818 additionally features spread spectrum oper-
APPLICATIONS
ation which significantly reduces the peak radiated and conducted noise on both the input and output supplies, n Automotive and Transportation making it easier to comply with electromagnetic interfer- n Industrial ence (EMI) standards. n Military/Avionics All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258.
TYPICAL APPLICATION
VOUT3
LTC7818 Response to a Cold LTC7818 Response to a Cold Crank
REGULATED TO 10V WHEN VIN < 10V VBIAS
Crank Automotive Waveform
150µF 22µF VFB3
Automotive Waveform
FOLLOWS VIN WHEN V TG3 TG1 IN >10V BOOST3 BOOST1 0.1µF 1.5mΩ 1.4µH 0.1µF 0.9µH 2mΩ VOUT1 VIN SW3 3.3V SW1 V 1V TO 38V 12A BATT 22µF 330µF STARTUP 150µF VOUT3 ABOVE 5V BG3 BG1 LTC7818 210k SENSE3– SENSE1+ SENSE3+ SENSE1– VOLTAGE VOUT3 RUN1,2,3 VFB1 VOUT3 68.1k 2V/DIV ITH1,2,3 TRACK/SS1,2,3 VOUT2 TG2 INTVCC BOOST2 VPRG3 0.1µF V 1.8µH 3mΩ V OUT1 0.1µF 4.7µF OUT2 5V SW2 10A BG2 10µF 330µF BOOST1,2,3 MODE SENSE2+ 357k PLLIN/SPREAD 0V SENSE2– TIME (10ms/DIV) 7818 TA01b FREQ VFB2 EXTV GND CC VOUT2 68.1k 7818 TA01a Rev. A Document Feedback For more information www.analog.com 1 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Diagram Operation Main Control Loop Power and Bias Supplies (VBIAS, EXTVCC, and INTVCC) Shutdown and Start-Up (RUN1, RUN2, RUN3 and TRACK/SS1, TRACK/SS2, SS3 Pins) Light Load Operation: Burst Mode Operation, Pulse-Skipping, or Forced Continuous Mode (MODE Pin) Frequency Selection, Spread Spectrum, and Phase-Locked Loop (FREQ and PLLIN/SPREAD Pins) Boost Controller Operation When VIN > VOUT Boost Controller at Low Input Voltage Buck Controller Output Overvoltage Protection Buck Foldback Current Channel 1 Power Good (PGOOD1) Boost Overvoltage Indicator (OV3) Applications Information Inductor Value Calculation Inductor Core Selection Current Sense Selection Low Value Resistor Current Sensing Inductor DCR Current Sensing Setting the Operating Frequency Selecting the Light-Load Operating Mode Power MOSFET Selection Boost CIN and COUT Selection Buck CIN and COUT Selection Setting the Buck Output Voltage Setting Boost Output Voltage (VPRG3 Pin) RUN Pins and Undervoltage Lockout Soft-Start and Tracking (TRACK/SS1, TRACK/SS2, SS3 Pins) Single Output Two-Phase Operation INTVCC Regulators Topside MOSFET Driver Supply (CB, DB) Minimum On-Time Considerations Boost Channel Current Monitor (IMON3) Fault Conditions: Buck Current Limit and Foldback Fault Conditions: Buck Overvoltage Protection (Crowbar) Fault Conditions: Overtemperature Protection Phase-Locked Loop and Frequency Synchronization Efficiency Considerations Checking Transient Response Buck Design Example PC Board Layout Checklist PC Board Layout Debugging Typical Applications Package Description Revision History Typical Application Related Parts
FEATURES DESCRIPTION
n
Dual Buck Plus Single Boost Synchronous Controllers
The LTC®7818 is a high performance triple output (buck/ n
Low Operating I
buck/boost) synchronous DC/DC switching regulator con-
Q:
n
14μA (14V to 3.3V, Channel 1 On)
troller that drives all N-channel power MOSFET stages. n
Outputs Remain in Regulation Through Cold Crank
Its constant-frequency current mode architecture allows a phase-lockable switching frequency of up to 3MHz.
Down to 1V Input Supply Voltage
n The LTC7818 operates from a wide 4.5V to 40V input
Wide Bias Input Voltage Range: 4.5V to 40V
n supply range. When biased from the output of the boost
Buck and Boost Output Voltages Up to 40V
n converter or another auxiliary supply, the LTC7818 can
Spread Spectrum Operation
operate from an input supply as low as 1V after start-up. n
RSENSE or DCR Current Sensing
n
Programmable Fixed Frequency (100kHz to 3MHz)
The LTC7818 synchronous boost PassThru capability n
PassThru™/100% Duty Cycle Capable for
minimizes losses in automotive start-stop applications.
Synchronous Boost MOSFET
The very low no-load quiescent current extends operating n run time in battery powered systems. OPTI-LOOP® com- Phase-Lockable Frequency (100kHz to 3MHz) n pensation allows the transient response to be optimized Selectable Continuous, Pulse-Skipping, or Low over a wide range of output capacitance and ESR values. Ripple Burst Mode Operation at Light Loads n The LTC7818 features a precision 0.8V reference for the Boost Channel Current Monitor Output bucks, 1.2V reference for the boost and a power good n Low Shutdown IQ: 1.5μA output indicator. n Small 40-Lead 6mm × 6mm QFN Package The LTC7818 additionally features spread spectrum oper-
APPLICATIONS
ation which significantly reduces the peak radiated and conducted noise on both the input and output supplies, n Automotive and Transportation making it easier to comply with electromagnetic interfer- n Industrial ence (EMI) standards. n Military/Avionics All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258.
TYPICAL APPLICATION
VOUT3
LTC7818 Response to a Cold LTC7818 Response to a Cold Crank
REGULATED TO 10V WHEN VIN < 10V VBIAS
Crank Automotive Waveform
150µF 22µF VFB3
Automotive Waveform
FOLLOWS VIN WHEN V TG3 TG1 IN >10V BOOST3 BOOST1 0.1µF 1.5mΩ 1.4µH 0.1µF 0.9µH 2mΩ VOUT1 VIN SW3 3.3V SW1 V 1V TO 38V 12A BATT 22µF 330µF STARTUP 150µF VOUT3 ABOVE 5V BG3 BG1 LTC7818 210k SENSE3– SENSE1+ SENSE3+ SENSE1– VOLTAGE VOUT3 RUN1,2,3 VFB1 VOUT3 68.1k 2V/DIV ITH1,2,3 TRACK/SS1,2,3 VOUT2 TG2 INTVCC BOOST2 VPRG3 0.1µF V 1.8µH 3mΩ V OUT1 0.1µF 4.7µF OUT2 5V SW2 10A BG2 10µF 330µF BOOST1,2,3 MODE SENSE2+ 357k PLLIN/SPREAD 0V SENSE2– TIME (10ms/DIV) 7818 TA01b FREQ VFB2 EXTV GND CC VOUT2 68.1k 7818 TA01a Rev. A Document Feedback For more information www.analog.com 1 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Diagram Operation Main Control Loop Power and Bias Supplies (VBIAS, EXTVCC, and INTVCC) Shutdown and Start-Up (RUN1, RUN2, RUN3 and TRACK/SS1, TRACK/SS2, SS3 Pins) Light Load Operation: Burst Mode Operation, Pulse-Skipping, or Forced Continuous Mode (MODE Pin) Frequency Selection, Spread Spectrum, and Phase-Locked Loop (FREQ and PLLIN/SPREAD Pins) Boost Controller Operation When VIN > VOUT Boost Controller at Low Input Voltage Buck Controller Output Overvoltage Protection Buck Foldback Current Channel 1 Power Good (PGOOD1) Boost Overvoltage Indicator (OV3) Applications Information Inductor Value Calculation Inductor Core Selection Current Sense Selection Low Value Resistor Current Sensing Inductor DCR Current Sensing Setting the Operating Frequency Selecting the Light-Load Operating Mode Power MOSFET Selection Boost CIN and COUT Selection Buck CIN and COUT Selection Setting the Buck Output Voltage Setting Boost Output Voltage (VPRG3 Pin) RUN Pins and Undervoltage Lockout Soft-Start and Tracking (TRACK/SS1, TRACK/SS2, SS3 Pins) Single Output Two-Phase Operation INTVCC Regulators Topside MOSFET Driver Supply (CB, DB) Minimum On-Time Considerations Boost Channel Current Monitor (IMON3) Fault Conditions: Buck Current Limit and Foldback Fault Conditions: Buck Overvoltage Protection (Crowbar) Fault Conditions: Overtemperature Protection Phase-Locked Loop and Frequency Synchronization Efficiency Considerations Checking Transient Response Buck Design Example PC Board Layout Checklist PC Board Layout Debugging Typical Applications Package Description Revision History Typical Application Related Parts
