“But despite the benefits that the LLC topology can offer, including minimal standby power and low audible noise, electric vehicle manufacturers have been hesitant to use the LLC topology because the limited operating input voltage range – automotive dc-dc converters need a wide input, output voltage support, or both, in order to maintain performance during cold-crank, transient or crash-related events,” according to the company. “Technological innovations in LLC controllers are enabling new use cases for the LLC topology in automotive charging applications.”
Called UCC25661x-Q1, the ICs operate across 50 to 750kHz at full-load, and implement ‘input-power proportional control’ (IPPC), a novel analogue-based feed-forward scheme which reduces the control signal’s dependency on switching frequency, thereby minimising the impact of input and output voltage variations.
“IPPC widens the control range of the LLC converter and simplifies the design of wide input applications such as high voltage to low voltage redundant auxiliary, key-off or bias isolated power supplies,” said TI. “IPPC also simplifies the design of wide output applications such as light electric vehicle chargers for scooters, mopeds, golf carts and fork lifts.”
Custom protections include an automatic capacitive region avoidance scheme along with the adaptive soft start with reverse recovery avoidance to ensure that the device does not work in a mode with the potential to damage the power switching FETs. “This scheme makes the controller ideal for working with a pre-biased load,” said TI.
More conventional protections include: 50ns over-current, cycle-by-cycle over-current, over-voltage, internal over-temperature, external over-temperature and under-voltage lock-out.
Additional modes include high frequency pulse skipping for improved light
load efficiency, and low frequency burst mode to lessen stand-by power.
+0.6A and -1.2A are available to drive the gates of the necessary external mosfets.
Three devices are planned: the basic UCC256613-Q1, then UCC256612-Q1 which integrates high voltage start-up, followed by a version, UCC256614-Q1, which further adds ‘extended gain range’ that among other things selectively disables PFC to work with wider input ranges.
Packaging is 9.9 x 3.9mm SOIC with pins removed to improve voltage performance.
Find TI’s e-bike charger designs here:
– Universal input 500W constant current and constant voltage e-bike charger (pictured)
– 750W off-board charger for light electric two-wheelers
Last year Samsung created a 1,000v 22nF COG multi-layer ceramic capacitor specifically for resonant topology on-board vehicle charges, although CLLC in this case.
