This paper presents YELLOWSTONE, a single chip, low-voltage, synchronous Buck DC-DC converter implementing a current mode PWM controller with built-in N & P-channel power MOSFETs. It aims to be used as a Point-of-Load (PoL) switched mode power supply with a maximum output current of 500mA. It generates from a typical +3.3V or +5V voltage input a lower voltage output between +0.9V and +3.3V configurable by an external resistor network. It has been specified and designed for operation at temperatures from −55°C to +225°C. Synchronous rectification increases efficiency and reduces external components count. The circuit achieves power efficiencies in excess of 90%. The chip implements a current mode PWM control which enables a fast response to line and load transient variations. A high switching frequency (1.5MHz typical with internal clock and up to 2MHz with external clock) has been selected enabling a dramatic reduction of the number and size of passive external components. The current mode control made possible to use a simple compensation loop and to integrate it. High integration level, tiny IC package (5mm*5.5mm) and small external passive components, lead to a very small footprint for the complete PoL function, i.e. as small as 0.25inch2 (10mm*15mm).
This paper presents two new tiny high-temperature adjustable voltage regulators. CHT-VEGA can regulate a 5V ±10% input voltage to an output within the range 1.1V to 3.6V and delivering up to 500mA at 225°C (junction). The output voltage is set by an external resistor divider and is maintained within +/−5% total accuracy in all load, line and temperature conditions. The second device, CHT-RIGEL, supports a wide input voltage range up to 30V; its output is adjustable between 1.8V and 24V, with up to 100mA capability at 225°C. Both chips feature a thermal shut-down with a threshold in the 250∼300°C range: the first over-temperature protection of this kind in high temperature devices. CISSOID created a new TDFP SMD package that combines tiny size and good thermal resistance. A detailed thermal characterization is presented, as well as what it means for the operating temperature, and the impact on PCB footprint and system cost. As a conclusion, will be highlighted the benefits of using such ICs rated 225°C at junction level, even if the ambient temperature of the application remains low (e.g. 175°C), and in particular the impact on reduction of the PCB footprint, compared to 175–210°C ratings.
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