Fast Synchronous Step-Down DC/DC Controller
Linear Technology Corporation introduces the LTC3833, a high frequency controlled on-time synchronous step-down DC/DC controller with differential output voltage sensing and clock synchronization. The controlled on-time, valley current-mode architecture forces a very fast transient response by increasing its operating frequency during a transient event, allowing the LTC3833 to recover from a large load step in only a few cycles. Its 4.5V to 38V input range encompasses a wide variety of applications including most intermediate bus voltages. Strong onboard N-channel MOSFET gate drivers allow the use of high power external MOSFETs for high load current, up to 25A in applications with output voltages ranging from 0.6V to 5.5V, making it ideal for point-of-load requirements. The LTC3833's differential amplifier provides true remote output voltage sensing of both the positive and negative terminals, enabling high accuracy regulation independent of IR losses (up to ±500mV) in trace runs, vias and interconnects. A low 20ns minimum on time allows for a high step-down ratio power supply at high frequency operation. The operating frequency is selectable from 200kHz to 2MHz or can be synchronized to an external clock. The output current is monitored by sensing the voltage drop across the output inductor (DCR) for highest efficiency or by using a sense resistor. Additional features include an onboard bias voltage LDO, soft-start or tracking, adjustable current limit, overvoltage protection, current limit foldback and external VCC control. The LTC3833 offers superior total differential regulation accuracy and is specified to account for all error sources including line, load and differential sensing. The LTC3833 total differential output voltage accuracy is +/-0.25% at 25°C, +/-0.67% from 0°C to 85°C and ±1% over the full -40°C to 125°C operating junction temperature range. Summary of Features: LTC3833
Linear Technology Corporation announces the LTC3852, a low/wide input voltage (2.7V to 5.5V or 4V-38V) synchronous step-down DC/DC controller. The device's onboard charge pump provides 5V bias to drive low RDS(ON) and standard logic-level power MOSFETs from a 3.3V nominal supply. Since the LTC3852's internal charge pump and DC/DC controller are independent, the charge pump output can provide 5V to power the internal gate drivers, and the DC/DC converter power stage can draw power from another source (up to 38V maximum). Output currents up to 25A can be supplied over an output voltage range from 0.8V to 99% of VIN (2.7V-5.5V), making the LTC3852 ideal for 3.3V-powered point-of-load applications. A constant-frequency, current-mode architecture allows a selectable fixed or phase-lockable (PLL) frequency from 250kHz to 750kHz. Selectable Burst Mode® operation, pulse skip or forced continuous mode is user controlled to optimize light load efficiency. OPTI-LOOP® compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values, including all ceramic input and output capacitors. Output current sensing is accomplished by measuring the voltage drop across the output inductor (DCR) for highest efficiency, or by using an optional sense resistor in series with the inductor for highest accuracy. Current foldback limits MOSFET heat dissipation during short-circuit and overload conditions. In addition, the LTC3852 has adjustable soft-start or tracking to control the turn-on characteristics of the supply, and features a precision 0.8V reference with an accuracy of ±1.25% over a -40°C to 125°C operating temperature range. With a maximum duty cycle of 99%, the LTC3852 has a very low dropout voltage, a useful feature for extending run times in battery-powered applications. Summary of Features: LTC3852
Linear Technology Corporation announces the LT3748H, a high input voltage isolated flyback DC/DC controller with guaranteed operation for junction temperatures as high as 150°C. This device significantly simplifies the design of an isolated DC/DC converter since there is no requirement for an opto-isolator, third winding or signal transformer for feedback, as the output voltage is sensed from the primary-side flyback signal. The LT3748 operates over a 5V to 100V input voltage range and drives an external N-channel power MOSFET, making it well suited for a wide variety of automotive, industrial, telecom and datacom applications. The LT3748 operates in a boundary mode, current-mode control switching scheme, resulting in +/-5% typical regulation over the full line, load and temperature range. Boundary mode also permits the use of a smaller transformer compared to equivalent continuous conduction mode designs. The output voltage is easily set by two external resistors and the transformer turns ratio. Several off-the-shelf transformers identified in the data sheet can be used for numerous applications. The high level of integration and the use of boundary mode operation results in a simple, clean application solution to the traditional challenge of isolated power delivery. Additional features include an onboard low drop regulator for IC power, programmable soft start, undervoltage lockout, adjustable current limit and output voltage temperature compensation. Summary of Features: LT3748H
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