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reference designLT8645S | Demoboard LT Journal V1.2018

Analog Devices LT8645S | Demoboard LT Journal V1.2018

65V, 8A Synchronous Step-Down Silent Switcher 2 with 2.5μA Quiescent Current

Overview

TopologyBuck Converter
Input voltage5.5-65 V
Switching frequency200-2000 kHz
Output 15 V / 8 A
IC revision1

Description

LTJournalThe LT®8645S/LT8646S synchronous step-down regulator features second generation Silent Switcher architecture designed to minimize EMI/EMC emissions while delivering high efficiency at high switching frequencies. This includes the integration of bypass capacitors to optimize all the fast current loops inside and make it easy to achieve advertised EMI performance by eliminating layout sensitivity. This performance makes the LT8645S/LT8646S ideal for noise sensitive applications and environments.The fast, clean, low-overshoot switching edges enable high efficiency operation even at high switching frequencies, leading to a small overall solution size. Peak current mode control with a 40ns minimum on-time allows high step-down ratios even at high switching frequencies. The LT8646S has external compensation via the VC pin to enable current sharing and fast transient response at high switching frequencies. A CLKOUT pin enables synchronizingother regulators to the LT8645S/LT8646S. Burst Mode® operation enables ultralow standby current consumption, pulse-skipping mode allows full switching frequency at lower output loads, or spread spectrum operation can further reduce EMI/EMC emissions.

Features

  • Silent Switcher®2 Architecture
  • Ultralow EMI/EMC Emissions on Any PCB
  • Eliminates PCB Layout Sensitivity
  • Internal Bypass Capacitors Reduce Radiated EMI
  • Optional Spread Spectrum Modulation
  • High Efficiency at High Frequency
  • Up to 95% Efficiency at 1MHz, 12VIN to 5VOUT
  • Up to 94% Efficiency at 2MHz, 12VIN to 5VOUT
  • Wide Input Voltage Range: 3.4V to 65V
  • Ultralow Quiescent Current Burst Mode Operation
  • 2.5A IQ Regulating 12VIN to 3.3VOUT (LT8645S)
  • Output Ripple < 10mVP-P
  • External Compensation: Fast Transient Response and Current Sharing (LT8646S)
  • Fast Minimum Switch On-Time: 40ns
  • Low Dropout Under All Conditions: 60mV at 1A
  • Adjustable and Synchronizable: 200kHz to 2.2MHz
  • Peak Current Mode Operation
  • Output Soft-Start and Tracking
  • Small 32-Lead 6mm × 4mm LQFN Package

Typical applications

  • GSM Power Supplies
  • General Purpose Step-Down
  • Automotive and Industrial Supplies

More information

Products

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74279226101
WE-MPSB EMI Multilayer Power Suppression Bead, 100 Ω, 160 Ω
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Status Activei| Production is active. Expected lifetime: >10 years.
Product seriesWE-MPSB EMI Multilayer Power Suppression Bead
Impedance @ 100 MHz100 Ω
Maximum Impedance160 Ω
Maximum Impedance1100 MHz 
Rated Current8000 mA
Impedance @ 1 GHz150 Ω
Height2.3 mm
TypeHigh Current