LTC3859A

PRODUCTION

Low IQ, Triple Output, Buck/Buck/Boost Synchronous Controller with Improved Burst Mode Operation

Data Sheet (Rev. B) Product Selection Table
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Overview

  • Dual Buck Plus Single Boost Synchronous Controllers
  • Outputs Remain in Regulation Through Cold Crank Down to 2.5V
  • Low Operating IQ: 55μA (One Channel On)
  • Wide Bias Input Voltage Range: 4.5V to 38V
  • Buck Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
  • Boost Output Voltage Up to 60V
  • RSENSE or DCR Current Sensing
  • 100% Duty Cycle for Boost Synchronous MOSFET Even in Burst Mode® Operation
  • Phase-Lockable Frequency (75kHz to 850kHz)
  • Programmable Fixed Frequency (50kHz to 900kHz)
  • Selectable Continuous, Pulse-Skipping or Low Ripple Burst Mode Operation at Light Loads
  • Very Low Buck Dropout Operation: 99% Duty Cycle
  • Adjustable Output Voltage Soft-Start or Tracking
  • Low Shutdown IQ: 14μA
  • Small 38-Pin 5mm × 7mm QFN and TSSOP Packages

The LTC3859A is a high performance triple output (buck/buck/boost) synchronous DC/DC switching regulator controller that drives all N-channel power MOSFET stages. Constant frequency current mode architecture allows a phase-lockable switching frequency of up to 850kHz. The LTC3859A operates from a wide 4.5V to 38V input supply range. When biased from the output of the boost converter or another auxiliary supply, the LTC3859A can operate from an input supply as low as 2.5V after start-up.

The 55μA no-load quiescent current extends operating runtime in battery powered systems. OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The LTC3859A features a precision 0.8V reference for the bucks, 1.2V reference for the boost and a power good output indicator. The PLLIN/MODE pin selects among Burst Mode operation, pulse-skipping mode, or continuous inductor current mode at light loads.

Compared to the LTC3859, the LTC3859A's boost controller has improved performance in Burst Mode operation when the input voltage is higher than the regulated output voltage.

Quiescent Current (Burst Mode) Notes
LTC3859AL 28μA-One channel on, Buck
38μA-All three channels on		 Internal clamp on the INTVCC pin
LTC3859A 55μA-One channel on, Buck
80μA-All three channels on		 Internal clamp on the INTVCC pin. For new designs, we recommend LTC3859AL
LTC3859 55μA-One channel on, Buck
80μA-All three channels on		 For new designs, we recommend LTC3859AL

Applications

  • Automotive Always-On and Start-Stop Systems
  • Battery Operated Digital Devices
  • Distributed DC Power Systems
  • Multioutput Buck-Boost Applications
LTC3859A
Low IQ, Triple Output, Buck/Buck/Boost Synchronous Controller with Improved Burst Mode Operation
Efficiency vs Input Voltage Product Package 1 Product Package 2
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Documentation

Data Sheet 1

Reliability Data 1

User Guide 1

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Software Resources

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Hardware Ecosystem

Parts Product Life Cycle Description
Circuit Monitors 1
LTC2960
RECOMMENDED FOR NEW DESIGNS 36V Nano-Current Two-Input Voltage Monitor
Protection Switches & Controllers 3
LTC4359
RECOMMENDED FOR NEW DESIGNS Ideal Diode Controller with Reverse Input Protection
LTC4364
RECOMMENDED FOR NEW DESIGNS Surge Stopper with Ideal Diode
LTC2955
RECOMMENDED FOR NEW DESIGNS Pushbutton On/Off Controller with Automatic Turn-On
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Tools & Simulations

LTspice

Models for the following parts are available in LTspice:

  • LTC3859
  • LTC3859AL

LTpowerCAD

Design tools for the following parts are available in LTpowerCAD:

  • LTC3859AL(BOOST)
  • LTC3859AL(BUCK)
LTspice

LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

Evaluation Kits

eval board
schematic 1
DC1425A

LTC3859A Demo Board | Triple Output, Buck/Buck/Boost, 4.5V ≤ VIN ≤ 36V, VOUT1 = 5V @ 5A, VOUT2 = 8.5V @ 3A, VOUT3 = 10V @ 2A

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Product Details

Demonstration circuit DC1425A is a triple output synchronous step-up/dual step-down power supply featuring the LTC3859AIFE. The demo board is has the LTC3859AIFE buck inputs supplied from the boost output. With this boost-then-buck topology, the buck outputs maintain regulation over the entire 4.5V to 36V input range and the application is suitable for automotive or other battery fed applications where low quiescent current is important. The buck controllers provide 5V @ 5A and 8.5V @ 3A and the boost can supply 10V @ 2A when the bucks are drawing their maximim load current.
DC1425A
LTC3859A Demo Board | Triple Output, Buck/Buck/Boost, 4.5V ≤ VIN ≤ 36V, VOUT1 = 5V @ 5A, VOUT2 = 8.5V @ 3A, VOUT3 = 10V @ 2A
DC1425A - Schematic

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