Features Typical APPLICATIO U1.5A, 500kHz Buck Switching Regulator

■Constant 500 khz switching frequency ■■All surface mount components use inductor size reduced to 5µh ■Easy Synchronizable ■Saturated switching design: 0.4? ■Effective supply current: 2.5ma ■Off current: 20µa

■Portable computers, battery powered systems, battery chargers, distributed power

The LT?1375/LT1376 are 500kHz monolithic step-down mode switching regulators. A 1.5A switch is mounted on the die along with all necessary oscillators, control circuits and logic circuits. The high switching frequency greatly reduces the size of external components. topology

It is a current type, with fast transient response and good loop stability. There are fixed output voltages and adjustable parts. A special high-speed bipolar process and new design techniques achieve high efficiency at high switching frequencies. Efficiency can be maintained over a wide range of output currents by using an output bias circuit and saturating the power switch with a power-supply boost capacitor. Turning off the signal will reduce the supply current by 20µA in two parts. The LT1375 can be externally synchronized from 580kHz to 900kHz via logic stage inputs. The LT1375/LT1376 are available in standard 8-pin PDIP and SO packages, as well as fused-lead 16-pin SO with lower thermal resistance. Provides full cycle short circuit protection and thermal shutdown. Use standard surface mount external components, including inductors and capacitors. For low input voltage applications with 3.3V output, see the LT1507. This is a functionally identical part that can operate between 4.5V and 12V from the input voltage.

This is the collector of the on-chip power NPN switch. When the bias pin is not present, this pin powers the internal circuitry and internal regulator. During NPN switching, a high dl/dt edge appears on this pin. Keep external bypass and capture diodes close to this pin. Any tracking inductance on this path will generate a voltage spike when the switch is off, increasing the VCE voltage of the internal NPN. Bias (LT1376 only): Bias pins are used to improve efficiency when operating at higher input voltages and lower load currents. Connecting this pin to the specified output voltage forces most internal circuits to draw operating current from the output voltage rather than the input supply. This is a more efficient way to handle if the input voltage is much higher than the output voltage. The minimum output voltage for this mode of operation is set to 3.3V. Efficiency increases by more than 10% at VIN = 20V, VOUT = 5V, IOUT = 25mA. SYNC (LT1375 only): The SYNC pin is used to synchronize the internal oscillator to an external signal. It is directly logic compatible and can be driven with any signal between 10% and 90% duty cycle. The synchronization range is equal to the initial operating frequency, up to 900kHz. For more information, see the Synchronization section in Application Information. FB/SENSE: The feedback pin is used to set the output voltage, using an external voltage divider to produce the desired output voltage of 2.42V at the pin. Fixed voltage (-5) section includes on-chip voltage divider and FB

The pin acts as a detection pin and connects directly to the 5V output. The FB pin performs two other functions. When the pin voltage drops below 1.7V, the switch current limit is reduced. Below 1V, the switching frequency also decreases.