Texas Instruments

The UCC3921 family of negative floating hot swap power managers provides complete power management, hot swap, and fault handling capability. The IC is referenced to the negative input voltage and is powered through an external resistor connected to ground, which is essentially a current drive as opposed to the traditional voltage drive. The onboard 10V shunt regulator protects the IC from excess voltage and serves as a reference for programming the maximum allowable output sourcing current during a fault. All control and housekeeping functions are integrated and externally programmable. These include the fault current level, maximum output sourcing current, maximum fault time, selection of Retry or Latched mode, soft start time, and average power limiting. In the event of a constant fault, the internal timer will limit the on time from less than 0.1% to a maximum of 3% duty cycle. The duty cycle modulation depends on the current into PL, which is a function of the voltage across the FET, thus limiting average power dissipation in the FET. The fault level is fixed at 50mV across the current sense amplifier to minimize total dropout. The fault current level is set with an external current sense resistor, while the maximum allowable sourcing current is programmed with a voltage divider from VDD to generate a fixed voltage on IMAX. The current level, when the output acts as a current source, is equal to VIMAX/RSENSE. If desired, a controlled current start up can be programmed with a capacitor on IMAX. When the output current is below the fault level, the output device is switched on. When the output current exceeds the fault level, but is less than the maximum sourcing level programmed by IMAX, the output remains switched on, and the fault timer starts charging CT. Once CTcharges to 2.5V, the output device is turned off and performs a retry some time later (provided that the selected mode of operation is Automatic Retry Mode). When the output current reaches the maximum sourcing current level, the output acts as a current source, limiting the output current to the set value defined by IMAX. Other features of the UCC3921 include undervoltage lockout, 8-pin Small Outline (SOIC) and Dual-In-Line (DIL) packages, and a Latched Operation Mode option, in which the output is latched off once CTcharges to 2.5V and stays off until either SDFLTCH is toggled (for greater than 1ms) or the IC is powered down and then back up. The UCC3921 family of negative floating hot swap power managers provides complete power management, hot swap, and fault handling capability. The IC is referenced to the negative input voltage and is powered through an external resistor connected to ground, which is essentially a current drive as opposed to the traditional voltage drive. The onboard 10V shunt regulator protects the IC from excess voltage and serves as a reference for programming the maximum allowable output sourcing current during a fault. All control and housekeeping functions are integrated and externally programmable. These include the fault current level, maximum output sourcing current, maximum fault time, selection of Retry or Latched mode, soft start time, and average power limiting. In the event of a constant fault, the internal timer will limit the on time from less than 0.1% to a maximum of 3% duty cycle. The duty cycle modulation depends on the current into PL, which is a function of the voltage across the FET, thus limiting average power dissipation in the FET. The fault level is fixed at 50mV across the current sense amplifier to minimize total dropout. The fault current level is set with an external current sense resistor, while the maximum allowable sourcing current is programmed with a voltage divider from VDD to generate a fixed voltage on IMAX. The current level, when the output acts as a current source, is equal to VIMAX/RSENSE. If desired, a controlled current start up can be programmed with a capacitor on IMAX. When the output current is below the fault level, the output device is switched on. When the output current exceeds the fault level, but is less than the maximum sourcing level programmed by IMAX, the output remains switched on, and the fault timer starts charging CT. Once CTcharges to 2.5V, the output device is turned off and performs a retry some time later (provided that the selected mode of operation is Automatic Retry Mode). When the output current reaches the maximum sourcing current level, the output acts as a current source, limiting the output current to the set value defined by IMAX. Other features of the UCC3921 include undervoltage lockout, 8-pin Small Outline (SOIC) and Dual-In-Line (DIL) packages, and a Latched Operation Mode option, in which the output is latched off once CTcharges to 2.5V and stays off until either SDFLTCH is toggled (for greater than 1ms) or the IC is powered down and then back up.

The UCC2946 is designed to provide accurate microprocessor supervision, including reset and watchdog functions. During power up, the device asserts a reset signalRESwith VDD as low as 1 V. The reset signal remains asserted until the VDD voltage rises and remains above the reset threshold for the reset period. Both reset threshold and reset period are programmable by the user. The UCC2946 is also resistant to glitches on the VDD line. OnceREShas been deasserted, any drops below the threshold voltage need to be of certain time duration and voltage magnitude to generate a reset signal. These values are shown in. An I/O line of the microprocessor may be tied to the watchdog input (WDI) for watchdog functions. If the I/O line is not toggled within a set watchdog period, programmable by the user,WDOis asserted. The watchdog function is disabled during reset conditions. The UCC2946 is available in 8-pin TSSOP (PW) package to optimize board space. The UCC2946 is designed to provide accurate microprocessor supervision, including reset and watchdog functions. During power up, the device asserts a reset signalRESwith VDD as low as 1 V. The reset signal remains asserted until the VDD voltage rises and remains above the reset threshold for the reset period. Both reset threshold and reset period are programmable by the user. The UCC2946 is also resistant to glitches on the VDD line. OnceREShas been deasserted, any drops below the threshold voltage need to be of certain time duration and voltage magnitude to generate a reset signal. These values are shown in. An I/O line of the microprocessor may be tied to the watchdog input (WDI) for watchdog functions. If the I/O line is not toggled within a set watchdog period, programmable by the user,WDOis asserted. The watchdog function is disabled during reset conditions. The UCC2946 is available in 8-pin TSSOP (PW) package to optimize board space.

The UCC3961 advanced primary-side startup controller is a unique solution that provides all the primary-side functions required for a single-ended, isolated, switch-mode power converter incorporating secondary-side PWM control. It is usable with a wide range of secondary control circuits and is especially well suited for systems where sophisticated handling of overload conditions is required. Secondary-side control assumes that output voltage and current measurements are interfaced directly to an output ground-referenced PWM stage that develops the power switch command for the supply. This digital PWM command can then be transmitted to the primary-side power switch through a simple and low-cost isolating pulse transformer. With secondary-side control, it is much easier to monitor and control the system load with tightly coupled analog control loops. Load-oriented features such as output current sharing and synchronous rectification are implemented more easily. The UCC3961 provides all the circuitry required on the primary side of a secondary-side controlled power supply. It features a free running 60-kHz to 360-kHz oscillator which is synchronizable to the secondary-side PWM signal and also has the ability to accept start/stop PWM commands from the isolating pulse-edge transformer (PET). The use of an extremely small and low-cost pulse transformer allows for higher converter bandwidth. This also eliminates the loop-gain variations due to initial accuracy and aging of an opto-coupler feedback element or the size penalty of a gate transformer. It also includes an undervoltage lockout circuit with 2-V hysteresis, a low-current startup with active low during UVLO, a soft-start capability, a 5-V reference and a high-current power output. Advanced features of UCC3961 allows implementation of initial startup with optional high-voltage disconnect after starting, and input voltage monitoring with turnoff for either undervoltage or overvoltage conditions. Other features include power-switch current protection, pulse-by-pulse current limiting, shutdown after a programmable delay and continuous input volt*second clamp. The UCC3961 also provides a multi purpose, bidirectional shutdown pin (SD), that can be used in conjunction with the devices on the START pin, to modify the converters behavior in overload conditions. The possible configurations include continuous-peak current limiting, delayed or immediate shutdown with full cycle soft restart or fully latched overcurrent shutdown. In a non-typical use, the UCC3961 can accommodate an analog feedback signal through an opto-isolator where the UCC3961 then can operate in voltage-mode control mode with primary-side peak current limiting. The UCC3961 and the UCC2961 are available in the 14-pin SOIC (D) and PDIP (P) packages. For applications where only startup and control are desired, a simplified version of this product is offered in an 8-pin package as the UCC2960 and UCC3960. The UCC3961 advanced primary-side startup controller is a unique solution that provides all the primary-side functions required for a single-ended, isolated, switch-mode power converter incorporating secondary-side PWM control. It is usable with a wide range of secondary control circuits and is especially well suited for systems where sophisticated handling of overload conditions is required. Secondary-side control assumes that output voltage and current measurements are interfaced directly to an output ground-referenced PWM stage that develops the power switch command for the supply. This digital PWM command can then be transmitted to the primary-side power switch through a simple and low-cost isolating pulse transformer. With secondary-side control, it is much easier to monitor and control the system load with tightly coupled analog control loops. Load-oriented features such as output current sharing and synchronous rectification are implemented more easily. The UCC3961 provides all the circuitry required on the primary side of a secondary-side controlled power supply. It features a free running 60-kHz to 360-kHz oscillator which is synchronizable to the secondary-side PWM signal and also has the ability to accept start/stop PWM commands from the isolating pulse-edge transformer (PET). The use of an extremely small and low-cost pulse transformer allows for higher converter bandwidth. This also eliminates the loop-gain variations due to initial accuracy and aging of an opto-coupler feedback element or the size penalty of a gate transformer. It also includes an undervoltage lockout circuit with 2-V hysteresis, a low-current startup with active low during UVLO, a soft-start capability, a 5-V reference and a high-current power output. Advanced features of UCC3961 allows implementation of initial startup with optional high-voltage disconnect after starting, and input voltage monitoring with turnoff for either undervoltage or overvoltage conditions. Other features include power-switch current protection, pulse-by-pulse current limiting, shutdown after a programmable delay and continuous input volt*second clamp. The UCC3961 also provides a multi purpose, bidirectional shutdown pin (SD), that can be used in conjunction with the devices on the START pin, to modify the converters behavior in overload conditions. The possible configurations include continuous-peak current limiting, delayed or immediate shutdown with full cycle soft restart or fully latched overcurrent shutdown. In a non-typical use, the UCC3961 can accommodate an analog feedback signal through an opto-isolator where the UCC3961 then can operate in voltage-mode control mode with primary-side peak current limiting. The UCC3961 and the UCC2961 are available in the 14-pin SOIC (D) and PDIP (P) packages. For applications where only startup and control are desired, a simplified version of this product is offered in an 8-pin package as the UCC2960 and UCC3960.