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High-Temperature Versatile Voltage-Mode PWM Controller
Keywords: PWM controller, high efficiency, multi architecture
A high temperature versatile voltage mode PWM controller has been developed, with in-specification performance achieved from -60degC to 230degC and above using a hitemp SOI process technology for long term reliability. The circuit features a voltage-mode PWM controller optimized for Buck-mode converters but it can also be advantageously used for other DCDC architectures such as Boost, Buck-boost, Push-pull and Flyback. Several functional features are implemented, including tunable hiccup short-circuit protection and complex functionalities for improved efficiency at low load currents (automatic synchronous-asynchronous mode switching in Buck-mode, pulse skipping logic with adjustable threshold). A reliable and low usage-cost soft-start ramp is integrated as well as a tunable maximum duty cycle limitation. The circuit can operate with input voltages from 4.5V to 50V. The PWM frequency can be boosted up to 800kHz in order to deal with high temperature compact inductor and capacitor constraints. It can also be synchronized on an external clock. The internal linear regulator (LDO) is also able to provide the supply of external drivers. Using external drivers such as the X-Rel XTR20411 (power nMOSFET with driver on a single die), a buck converter demonstration board has been developed. By default, it operates at 400kHz with an output LC of 10uH and 10uF respectively and able to provide output voltages from 1.2V to 90%Vin (5V nominal). Obtained efficiencies for load currents above 500mA are above 90% at 2V dropout. The demonstration board provides outstanding efficiencies of more than 70% and 50% at 10mA load current for dropouts of 2V and 15V, respectively. The efficiency at low load current can even be further improved by feeding back the nominal 5V output of the converter to a dedicated PWM terminal. In this case, after startup, the internal LDO goes off and the controller is self powered by the DCDC output voltage.
Fabien Laplace, Design Expert
X-REL Semiconductor
Grenoble, Isere

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