LTC3521 - 1A Buck-Boost DC/DC and Dual 600mA Buck DC/DC Converters


  • Three High Efficiency DC/DC Converters:
    Buck-Boost (VOUT: 1.8V to 5.25V, IOUT: 1A)
    Dual Buck (VOUT: 0.6V to VIN, IOUT: 600mA)
  • 1.8V to 5.5V Input Voltage Range
  • Pin-Selectable Burst Mode® Operation
  • 30μA Total Quiescent Current in Burst Mode Operation
  • Independent Power Good Indicator Outputs
  • Integrated Soft-Start
  • Thermal and Overcurrent Protection
  • <2μA Current in Shutdown
  • Small 4mm × 4mm QFN and Thermally Enhanced TSSOP Packages

Typical Application

LTC3521 Typical Application
LTC3521 Typical Application


The LTC®3521 combines a 1A buck-boost DC/DC converter and dual 600mA synchronous buck DC/DC converters. The 1.1MHz switching frequency minimizes the solution footprint while maintaining high efficiency. All three converters feature soft-start and internal compensation to minimize the solution footprint and simplify the design process.

The buck converters are current mode controlled and utilize an internal synchronous rectifier to improve efficiency. The buck converters support 100% duty cycle operation to extend battery life. If the PWM pin is held low, the buck converters automatically transition from Burst Mode operation to PWM mode at high loads. With the PWM pin held high, the buck converters remain in low noise, 1.1MHz PWM mode.

The buck-boost converter features continuous conduction operation to maximize efficiency and minimize noise. At light loads, the buck-boost converter can be operated in Burst Mode operation to improve efficiency and reduce no-load standby current.

The LTC3521 provides a <2μA shutdown mode, overtemperature shutdown and current limit protection on all converters. The LTC3521 is available in a 24-pin 0.75mm × 4mm × 4mm QFN package, and a 20-pin thermally enhanced TSSOP package.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LTC3521EFE#PBF TSSOP-20 FE E 05-08-1663 (CB) Yes
LTC3521EFE#TRPBF TSSOP-20 FE E 05-08-1663 (CB) Yes
LTC3521EUF#PBF 4x4 QFN-24 UF E 05-08-1697 Yes
LTC3521EUF#TRPBF 4x4 QFN-24 UF E 05-08-1697 Yes
LTC3521IFE#PBF TSSOP-20 FE I 05-08-1663 (CB) Yes
LTC3521IFE#TRPBF TSSOP-20 FE I 05-08-1663 (CB) Yes
LTC3521IUF#PBF 4x4 QFN-24 UF I 05-08-1697 Yes
LTC3521IUF#TRPBF 4x4 QFN-24 UF I 05-08-1697 Yes

LTC3521 Package Drawing
LTC3521 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LTC3521EFE#PBF TSSOP-20 E $4.93 $3.45 Yes
LTC3521EFE#TRPBF TSSOP-20 E $3.51 Yes
LTC3521EUF#PBF 4x4 QFN-24 E $4.64 $3.25 Yes
LTC3521EUF#TRPBF 4x4 QFN-24 E $3.31 Yes
LTC3521IFE#PBF TSSOP-20 I $5.67 $3.97 Yes
LTC3521IFE#TRPBF TSSOP-20 I $4.03 Yes
LTC3521IUF#PBF 4x4 QFN-24 I $5.34 $3.74 Yes
LTC3521IUF#TRPBF 4x4 QFN-24 I $3.80 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC1389A LTC3521EUF Demo Board | Buck-Boost Plus Dual Buck, 2.4V ≤ VIN ≤ 5V, Vout1 = 3.3V @ 0.8A, Vout2=1.2V @ 0.6A, Vout3 = 1.8V @ 0.6A $125.00
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