LTC3851A - Synchronous Step-Down Switching Regulator Controller


  • Wide VIN Range: 4V to 38V Operation
  • RSENSE or DCR Current Sensing
  • ±1% Output Voltage Accuracy
  • Phase-Lockable Fixed Frequency: 250kHz to 750kHz
  • Dual N-Channel MOSFET Synchronous Drive
  • Very Low Dropout Operation: 99% Duty Cycle
  • Adjustable Output Voltage Soft-Start or Tracking
  • Output Current Foldback Limiting
  • Output Overvoltage Protection
  • 5V Internal Regulator
  • OPTI-LOOP® Compensation Minimizes COUT
  • Selectable Continuous, Pulse-Skipping or Burst Mode® Operation at Light Loads
  • Low Shutdown IQ: 20μA
  • VOUT Range: 0.8V to 5.5V
  • Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow SSOP or 3mm × 3mm QFN Package

Typical Application

LTC3851A Typical Application
LTC3851A Typical Application


The LTC3851A is a high performance synchronous step-down switching regulator controller that drives an all N-channel synchronous power MOSFET stage. A constant frequency current mode architecture allows a phase‑lockable frequency of up to 750kHz.

OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The LTC3851A features a precision 0.8V reference that is compatible with a wide 4V to 38V input supply range.

The TK/SS pin ramps the output voltage during start‑up. Current foldback limits MOSFET heat dissipation during short-circuit conditions. The MODE/PLLIN pin selects among Burst Mode operation, pulse-skipping mode or continuous inductor current mode at light loads and allows the IC to be synchronized to an external clock. The LTC3851A contains an improved PLL compared to the LTC3851.

The LTC3851A-1 is a version with a power good output signal instead of adjustable current limit.

LTC3851 Not Recommended For New Designs
LTC3851-1 Not Recommended For New Designs
LTC3851A Adjustable Current Limit
LTC3851A-1 PGOOD Output


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

Part Number Package Code Temp Package
LTC3851AEGN#PBF SSOP-16 GN E 05-08-1641 (GN16) RoHS
LTC3851AEGN#TRPBF SSOP-16 GN E 05-08-1641 (GN16) RoHS
LTC3851AEMSE#PBF MS-16E MSE E 05-08-1667 RoHS
LTC3851AEMSE#TRPBF MS-16E MSE E 05-08-1667 RoHS
LTC3851AEUD#PBF 3x3 QFN-16 UD E 05-08-1691 RoHS
LTC3851AEUD#TRPBF 3x3 QFN-16 UD E 05-08-1691 RoHS
LTC3851AHMSE#PBF MS-16E MSE H 05-08-1667 RoHS
LTC3851AHMSE#TRPBF MS-16E MSE H 05-08-1667 RoHS
LTC3851AIGN#PBF SSOP-16 GN I 05-08-1641 (GN16) RoHS
LTC3851AIGN#TRPBF SSOP-16 GN I 05-08-1641 (GN16) RoHS
LTC3851AIMSE#PBF MS-16E MSE I 05-08-1667 RoHS
LTC3851AIMSE#TRPBF MS-16E MSE I 05-08-1667 RoHS
LTC3851AIUD#PBF 3x3 QFN-16 UD I 05-08-1691 RoHS
LTC3851AIUD#TRPBF 3x3 QFN-16 UD I 05-08-1691 RoHS
LTC3851AMPMSE#PBF MS-16E MSE MP 05-08-1667 RoHS

LTC3851A Package Drawing
LTC3851A Package Drawing
LTC3851A 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
LTC3851AEGN#PBF SSOP-16 E $2.44 $1.71 Yes
LTC3851AEGN#TRPBF SSOP-16 E $1.77 Yes
LTC3851AEMSE#PBF MS-16E E $2.44 $1.71 Yes
LTC3851AEMSE#TRPBF MS-16E E $1.77 Yes
LTC3851AEUD#PBF 3x3 QFN-16 E $2.44 $1.71 Yes
LTC3851AEUD#TRPBF 3x3 QFN-16 E $1.77 Yes
LTC3851AHMSE#PBF MS-16E H $3.20 $2.24 Yes
LTC3851AHMSE#TRPBF MS-16E H $2.30 Yes
LTC3851AIGN#PBF SSOP-16 I $2.77 $1.94 Yes
LTC3851AIGN#TRPBF SSOP-16 I $2.00 Yes
LTC3851AIMSE#PBF MS-16E I $2.77 $1.94 Yes
LTC3851AIMSE#TRPBF MS-16E I $2.00 Yes
LTC3851AIUD#PBF 3x3 QFN-16 I $2.77 $1.94 Yes
LTC3851AIUD#TRPBF 3x3 QFN-16 I $2.00 Yes
LTC3851AMPMSE#PBF MS-16E MP $7.56 $5.29 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
DC1432A-A LTC3851AUED Demo Board with Adj ILIMIT | 4.5V ≤ VIN ≤ 14V, VOUT = 1.5V @ 15A $100.00
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