LTC1267 LTC1267-ADJ/LTC1267-ADJ5 Dual High Efficiency Synchronous Step-Down Switching Regulators OBSOLETE: FOR INFORMATION PURPOSES ONLY Contact Linear Technology for Potential Replacement DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ U ■ The LTC®1267 series are dual synchronous step-down switching regulator controllers featuring automatic Burst ModeTM operation to maintain high efficiencies at low output currents. The LTC1267 is composed of two separate regulator blocks, each driving a pair of external complementary power MOSFETs at switching frequencies up to 400kHz. The LTC1267 uses a constant off-time currentmode architecture to provide constant ripple current in the inductor and provide excellent line and load transient response. Dual Outputs: 3.3V and 5V, Two Adjustables or Adjustable and 5V Wide VIN Range: 4V to 40V Ultra-High Efficiency: Up to 95% Low Supply Current in Shutdown: 20µA Current Mode Operation for Excellent Line and Load Transient Response High Efficiency Maintained Over a Wide Output Current Range Independent Micropower Shutdown Very Low Dropout Operation: 100% Duty Cycle Synchronous FET Switching for High Efficiency Available in Standard 28-Pin SSOP APPLICATI A separate pin and on-board switch allow the MOSFET driver power to be derived from the regulated output voltage, providing significant efficiency improvement when operating at high input voltage. The output current level is user-programmable via an external current sense resistor. S UO ■ ■ ■ ■ The LTC1267 series is ideal for applications requiring dual output voltages with high conversion efficiencies over a wide load current range in a small amount of board space. Notebook and Palmtop Computers Battery-Operated Digital Devices Portable Instruments DC Power Distribution Systems , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. TYPICAL APPLICATI UO + CIN3 100µF 50V + VIN 5.4V to 25V + 3.3µF 1N4148 VOUT3 3.3V 2A L3 20µH 0.1µF 4 5 0.15µF VCC3 3 CAP3 1 2 VCC VIN PGATE 3 PDRIVE 3 14 SENSE + 3 13 12 SENSE – 3 1000pF D3 MBRS140T3 + COUT3 220µF 10V ×2 6 N-CH Si9410DY + 1N4148 8 P-CH Si9435DY RSENSE3 0.05Ω 0.15µF SHDN3 NGATE 3 PGND3 SGND3 CT3 7 11 9 27 26 28 1 MSHDN CAP5 EXT VCC VCC5 25 PGATE 5 24 PDRIVE 5 + 5 18 SENSE LTC1267 17 SENSE – 5 19 SHDN5 23 NGATE 5 ITH3 10 ITH5 15 CT5 SGND5 PGND5 16 20 22 P-CH Si9435DY 0.1µF L5 33µH 3.3µF RSENSE5 0.05Ω RC3 1k RC5 1k SHDN3, SHDN5, MSHDN 0V = NORMAL, >2V = SHDN VOUT5 5V 2A 1000pF D5 MBRS140T3 N-CH Si9410DY + CC3 CC5 CT3 CT5 270pF 3300pF 3300pF 270pF RSENSE3: KRL SL-1R050J L3: COILTRONICS CTX20-4 CIN5 100µF 50V COUT5 220µF 10V ×2 RSENSE5: KRL SL-1R050J L5: COILTRONICS CTX33-4 LTC1267 • F01 Figure 1. High Efficiency Dual 3.3V, 5V 1