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Complete Ride-Through DC/DC IC Provides 1A of Uninterrupted Output Current from Main Input or Single Supercapacitor Backup Supply

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MILPITAS, CA – March 10, 2014 – Linear Technology Corporation introduces the LTC3355, a complete ride-through DC/DC system IC. The LTC3355 features a main buck regulator with a built-in boost converter for temporary backup, or ride-through, of VOUT during a sudden loss of VIN power from a single supercapacitor energy source. The device includes all functions necessary to provide seamless charging of a supercapacitor (or other storage element), including the monitoring of VIN, VOUT and VCAP and automatic switchover to backup power. The LTC3355’s nonsynchronous constant frequency current mode monolithic 1A buck switching regulator provides a 2.7V to 5V regulated output voltage from an input supply up to 20V. The device is ideal for ride-through, “dying gasp” or data backup supplies commonly used in power meters, industrial alarms and solid state drives.

 The LTC3355 uses a 1A programmable constant-current/constant-voltage (CC/CV) linear charger powered from VOUT to charge a single supercapacitor, electrolytic capacitor or NiMH battery. A thermal regulation loop maximizes charge current while limiting the die temperature to 110°C. When the VIN supply drops below the programmable power-fail comparator input (PFI) threshold, the device’s constant frequency nonsynchronous current mode 5A boost switching regulator delivers power from the supercapacitor to VOUT. Backup power can be delivered to VOUT with capacitor voltages as low as 0.5V. The device has programmable boost, charger and VIN current limits. Other features include a VIN power fail indicator, VCAP power good indicator, and VOUT power-on reset (POR) output.

The LTC3355 is available in a thermally enhanced 20-lead, low-profile (0.75mm)
4mm x 4mm QFN package. The device operates over a -40°C to 125°C junction temperature range and is available from stock. Pricing starts at $3.25 each for the E grade in 1,000-piece quantities. For more information, visit www.linear.com/product/LTC3355

Complete Ride-Through DC/DC System IC

Summary of Features: LTC3355

• VIN Voltage Range: 3V to 20V
• VOUT Voltage Range: 2.7V to 5V
• 1A Current-Mode Buck Main Regulator
• 5A Boost Backup Regulator Powered from Single Supercapacitor
• Boost Regulator Operates Down to 0.5V for Maximum Utilization
of Supercapacitor Energy
• Programmable Supercapacitor Charge Current to 1A with Overvoltage Protection
• Charger Supports Single Cell CC/CV Battery Charging
• Programmable VIN Current Limit
• Programmable Boost Current Limit
• VIN Power Fail Indicator
• VCAP Power Good Indicator
• VOUT Power On Reset Output
• Compact 20-Lead 4mm × 4mm x 0.75mm QFN Package

Background:
Many applications require a few seconds of backup time in the event that system power is lost. For example, power fail alarm systems with radio alerts upon power failure or data backup systems that must store data upon power failure.

 

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Providing capacitor backup power requires four essential blocks. Here are the basic building blocks of a typical system normally powered from a 12V supply:
1) A 12V 4V buck dc/dc for main power
2) A linear cap charger that is powered off the buck output for maximum efficiency and minimum charge time
3) A high current, low input voltage backup power boost dc/dc converter for holding up the 4V rail as long as possible using just the stored energy in the supercap is its input supply.
4) A lossless OR’ing function for seamless switchover from buck to boost during a power failure

Introduction

The LTC3355 integrates all these system blocks into one monolithic device. It is a complete ride-through DC/DC system IC. The LTC3355 features a buck regulator with a built-in backup converter to allow temporary backup, or ride through, of VOUT during a sudden loss of VIN power. The IC contains all functions necessary to provide seamless charging of a supercapacitor (or other storage element), monitoring of VIN, VOUT and VCAP, and automatic switchover to backup power. The LTC3355’s monolithic 1A buck switching regulator provides a 2.7V to 5V regulated output voltage from an input supply of up to 20V. The 5A boost backup regulator maintains VOUT regulation when VIN power is lost, and can operate with a capacitor voltage as low as 0.5V.

Here are the device’s development motivations:
• Provide additional operating time after VIN power is lost
• Integrate all blocks necessary to provide up to 5W of uninterrupted power from 3V to 20V input or a single supercapacitor

Key Technical Features

• VIN Voltage Range: 3V to 20V
• VOUT Voltage Range: 2.7V to 5V
• 1A Current Mode Buck Main Regulator
• 5A Boost Backup Regulator Powered from Single Supercapacitor
• Boost Regulator Operates Down to 0.5V for
Maximum Utilization of Supercapacitor Energy
• Programmable Supercapacitor Charge Current to 1A with Overvoltage Protection
• Charger Supports Single Cell CC/CV Battery Charging
• Programmable VIN Current Limit
• Programmable Boost Current Limit
• VIN Power Fail Indicator
• VCAP Power Good Indicator
• VOUT Power On Reset Output
• Compact 20-Lead 4mm × 4mm QFN Package

Target Applications
• Smart grid power fail alarms
• Industrial alarms, “dying gasp” supplies
• Data backup

 

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