Dual Output High Efficiency Converter Produces 3.3V and 8.5V Outputs from a 9V to 60V Rail

2010-07-01

745.31 K

The LTC3890 dual output DC/DC controller brings a unique combination of high performance features to applications that require low voltage outputs from high voltage inputs. It can produce two output voltages ranging from 0.8V to 24V from an input voltage of 4V to 60V. It is also very efficient, with a no-load quiescent current of only 50µA.

Many high-input-voltage step-down DC/DC converter designs use a transformer-based topology or external high side drivers to operate from up to 60V_IN. Others use an intermediate bus converter requiring an additional power stage. However, the LTC3890 simplifies design, with its smaller solution size, reduced cost and shorter development time compared to other design alternatives.

Feature Rich

The LTC3890 is a high performance synchronous buck DC/DC controller with integrated N-channel MOSFET drivers. It uses a current mode architecture and operates from a phase-lockable fixed frequency from 50kHz to 900kHz. The device features up to 99% duty cycle capability for low voltage dropout applications, adjustable soft-start or voltage tracking and selectable continuous, pulse-skipping or Burst Mode operation with a no-load quiescent current of only 50µA. These features, combined with a minimum on-time of just 95ns, make this controller an ideal choice for high step-down ratio applications. Power loss and supply noise are minimized by operating the two output stages out-of-phase.

Dual Output Application

Figure 1 shows the LTC3890 operating in an application that converts a 9V to 60V input into 3.5V/5A and 8.5V/3A outputs. The transient response for the 3.3V output with a 4A load step is less than 50mV (as shown in Figure 2).

Figure 1. High efficiency dual 8.5V/3.3V output step-down converter.

Figure 2. Transient response of 3.3V channel.

Figure 3 shows the efficiency of the 8.5V channel with a 36V input voltage.

Figure 3. Efficiency of the converter in Figure 1 for the V_OUT2 8.5V channel.

Single Output Application

The LTC3890 can also be configured as a 2-phase single output converter by simply connecting the two channels together. For example, a 9V to 60V input can be converted to an 8.5V output at 6A. Figure 4 shows the efficiency of this configuration at input voltages of 10V, 30V and 60V.

Figure 4. Efficiency of the LTC3890 configured as a 2-phase single output of 8.5V at up to 6A.

Current mode control provides good current balance between the phases.

Less than 10% mismatch can be achieved, as shown in Figure 5.

Figure 5. The inductor current in a 2-phase single output converter. Currents in both inductors shown with a 24V Input and 8.5V at 6A output.

Conclusion

Although there are many choices in dual-output controllers, the LTC3890 brings a new level of performance with its high voltage operation, high efficiency conversion and ease of design.

关于作者

Victor Khasiev

Victor Khasiev曾是ADI公司的高级应用工程师，在AC/DC和DC/DC转换的电力电子领域拥有丰富的经验。他拥有两项专利，并撰写了多篇文章。这些文章涉及ADI半导体器件在汽车和工业应用中的使用，涵盖了升压、降压、SEPIC、正-负、负-负、反激式、正激式转换器和双向备用电源。他持有高效功率因数校正解决方案和先进的栅极驱动器相关专利。Victor乐于为ADI公司客户提供技术支持解答有关ADI产品、电源原理图设计和验证、印刷电路板布...