JAJSMY4 September 2021 UCC14240-Q1
UCC14240-Q1 device is suitable for applications that have limited board space and require more integration. These devices are also suitable for very-high voltage applications, where power transformers meeting the required isolation specifications are bulky and expensive. The low-profile, low-center of gravity, and low weight provides a higher vibration tolerance than systems using large bulky transformers. The device is easy-to-use and provides flexibility to adjust both positive and negative output voltages as needed when optimizing the gate voltage for maximum efficiency while protecting gate oxide from over-stress with its tight voltage regulation accuracy.
The device integrates a high-efficiency, low-emissions isolated DC/DC converter for powering the gate drive of SiC or IGBT power devices in traction inverter motor drives, industrial motor drives, or other high voltage DC/DC converters. This DC/DC converter provides greater than 1.5 W of power across a 3000 VRMS basic isolation barrier.
The integrated DC/DC converter uses switched mode operation and proprietary circuit techniques to reduce power losses and boost efficiency. Specialized control mechanisms, clocking schemes, and the use of an on- chip transformer provide high efficiency and low radiated emissions.
The integrated transformer provides power delivery throughout a wide temperature range while maintaining a 3000-VRMS isolation, and an 850-VRMS continuous working voltage. The low isolation capacitance of the transformer provides high CMTI allowing fast dv/dt switching and higher switching frequencies, while emitting less noise.
The VIN supply is provided to the primary-side power controller that switches the input stage connected to the integrated transformer. Power is transferred to the secondary-side output stage, and regulated to a level set by the resistor divider connected between the (VDD – VEE) pin and the FBVDD pin with respect to the VEE pin. The output voltage is adjustable with external resistor divider allowing a wide (VDD – VEE) range.
For optimal performance ensure to maintain the VIN input voltage within the recommended operating voltage range. Do not exceed the absolute maximum voltage rating to avoid over-stressing the input pins.
A fast hysteretic feedback burst control loop monitors (VDD – VEE) and ensures the output voltage is kept within the hysteresis with low overshoots and undershoots during load and line transients. The burst control loop enables efficient operation across full load and allows a wide VOUT adjustability throughout the whole VIN range. The undervoltage lockout (UVLO) protection monitors the input voltage pin, VIN, with hysteresis and input filter ensuring robust system performance under noisy conditions. The overvoltage lockout (OVLO) protection monitors the input voltage pin, VIN, protects against over-voltage stress by disabling switching and reducing the internal peak voltage. Controlled soft-start timing, provided throughout the full power-up time, limits the peak input inrush current while charging the output capacitor and load.
The UCC14240-Q1 also provides a second output rail, (COM – VEE), that is used as a negative bias for the gate drivers, allowing quicker turn-off switching for the IGBTs, and also to protect from unwanted turn-on during fast switching of SiC devices. (COM – VEE) is a simple, yet fast and efficient bias controller to ensure the positive and negative rails are regulated during the PWM switching. The COM pin can be connected from the source of SiC device or emitter of and IGBT device. An external current limiting resistor allows the designer to program the sink and source current peak according to the needs of the gate drive system.
A fault protection and powergood status pin provides a mechanism for the host controller to monitor the status of the DC/DC converter and provide proper sequencing of power and PWM control signals to the gate driver. Fault protection includes undervoltage, overvoltage, over-temperature shutdown, and isolated channel communication interface watchdog timer.
A typical soft-start ramp-up time is approximately 3 ms, but varies based on input voltage, output voltage, output capacitance, and load. If either output is shorted or over-loaded, the device is not able to power-up within the 16-ms soft-start watch-dog-timer protection time, so the device latches off for protection. The latch can be reset by toggling the ENA pin or powering VIN down and up.
The output load must be kept low until start-up is complete and /PG pin is low. When powering up, do not apply a heavy load to (VDD – VEE) or (COM – VEE) outputs until the /PG pin has indicated power is good (pulling logic low) to avoid problems providing the power to ramp-up the voltage.
TI recommends to use the /PG status indicator as a trigger point to start the PWM signal into the gate driver. /PG output removes any ambiguity as to when the outputs are ready by providing a robust closed loop indication of when both (VDD –VEE) and (COM – VEE) outputs have reached their regulation threshold within ±10%.
Do not allow the host to begin PWM to gate driver until after /PG goes low. This action typically occurs less than 16 ms after VIN > UVLOp and ENA goes high. The /PG status output indicates the power is good after soft-start of (VDD – VEE) and (COM – VEE) and are within ±10% of regulation.
If the host is not monitoring /PG, then ensure that the host does not begin PWM to gate driver until 20 ms after VIN > UVLOp and ENA goes high in order to allow enough time for power to be good after soft-start of VDD and VEE.