Design Considerations
The challenges faced by Telecom DC/DC power supply
developers today include achieving high efficiency, high integration
(reduction in physical solution size), low system cost, ease of
development. Power topologies such as active-clamp forward, half
bridge, and full bridge are commonly employed in today’s designs to
addressing these needs. A Telecom DC/DC power supply usually converts
-48V to some intermediate voltage. Designs are typically comprised of a
PWM controller geared toward a specific topology and MOSFET drivers.
Certain PWM Controllers may integrate the MOSFET drivers.
The Telecom DC/DC market is usually dictated by brick size (full, half, quarter, eighth or sixteenth). The emergence of eighth and sixteenth bricks have resulted in new demand for the half-bridge converter, since the power levels in these packages are more in tune with those at which the half bridge topology excels. Along with reduction in physical size and an increase in power density, there is also an increasing number of features being added to the DC/DC converters that are required from a system level. These features include prebias startup, tracking, controlled startup and controlled shutdown capabilities. TI’s PWM controllers provide complete control functionality for each of the above requirements.
The center of the power supply is the controller, and it can be referenced to either the primary or secondary side ground. Both configurations can use a scheme where bias power for the controller is initially derived from a startup circuit; prior to a more efficient auxiliary winding of the transformer taking over once steady state operation is reached. A problem with the secondary side controller is that the bias power must come from the primary side (which has the wrong ground), upon power up. This problem can be overcome by using a separate isolated bias power converter to supply the current needed by the controller. This separate power supply can guarantee proper startup under all conditions.
Primary and Secondary side control each has advantages and disadvantages. In primary side control, the feedback signal must go from secondary side to primary side via isolation. This feedback will suffer from phase delay, which will hinder the control loop bandwidth and ultimately the response of the converter. Many converters use FETs for Synchronous Rectification and these require carefully managed gate drive. Hence, secondary side control has advantages in that it can directly drive these synchronous rectifiers, leading to improved response and higher performance over primary side control. Primary side control has advantages in that many designers are familiar with it, and that it is less complex.
Texas Instruments' portfolio of MOSFET drivers includes both primary side drivers as well as synchronous rectifier drivers. The UCC2720x family is recommended as a 120V primary side MOSFET driver. For applications that require greater efficiency and density, Synchronous Rectification is recommended to improve the efficiency of the power-subsystems' secondary-side circuitry. The TPS2822x driver family is recommended for Synchronous Rectification.
TI’s Integrated Hot Swap Power Controllers are optimized for nominal -48V systems. The devices provide load current slew rate control and peak magnitude limiting. Most of the Hot Swap Controllers have digital interface for precise programming and monitoring and also have Power good and fault outputs.
Other high-performance analog parts are also available to provide critical system functions and features such as sensor feedback, isolation, communication transceivers.(Telecom DC/DC Module. Analog circuits)
The Telecom DC/DC market is usually dictated by brick size (full, half, quarter, eighth or sixteenth). The emergence of eighth and sixteenth bricks have resulted in new demand for the half-bridge converter, since the power levels in these packages are more in tune with those at which the half bridge topology excels. Along with reduction in physical size and an increase in power density, there is also an increasing number of features being added to the DC/DC converters that are required from a system level. These features include prebias startup, tracking, controlled startup and controlled shutdown capabilities. TI’s PWM controllers provide complete control functionality for each of the above requirements.
The center of the power supply is the controller, and it can be referenced to either the primary or secondary side ground. Both configurations can use a scheme where bias power for the controller is initially derived from a startup circuit; prior to a more efficient auxiliary winding of the transformer taking over once steady state operation is reached. A problem with the secondary side controller is that the bias power must come from the primary side (which has the wrong ground), upon power up. This problem can be overcome by using a separate isolated bias power converter to supply the current needed by the controller. This separate power supply can guarantee proper startup under all conditions.
Primary and Secondary side control each has advantages and disadvantages. In primary side control, the feedback signal must go from secondary side to primary side via isolation. This feedback will suffer from phase delay, which will hinder the control loop bandwidth and ultimately the response of the converter. Many converters use FETs for Synchronous Rectification and these require carefully managed gate drive. Hence, secondary side control has advantages in that it can directly drive these synchronous rectifiers, leading to improved response and higher performance over primary side control. Primary side control has advantages in that many designers are familiar with it, and that it is less complex.
Texas Instruments' portfolio of MOSFET drivers includes both primary side drivers as well as synchronous rectifier drivers. The UCC2720x family is recommended as a 120V primary side MOSFET driver. For applications that require greater efficiency and density, Synchronous Rectification is recommended to improve the efficiency of the power-subsystems' secondary-side circuitry. The TPS2822x driver family is recommended for Synchronous Rectification.
TI’s Integrated Hot Swap Power Controllers are optimized for nominal -48V systems. The devices provide load current slew rate control and peak magnitude limiting. Most of the Hot Swap Controllers have digital interface for precise programming and monitoring and also have Power good and fault outputs.
Other high-performance analog parts are also available to provide critical system functions and features such as sensor feedback, isolation, communication transceivers.(Telecom DC/DC Module. Analog circuits)
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