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Robust True Low-dropout Linear Voltage Regulator and Digitally Tunable Buffered Precision Voltage Reference for High-Temperature, Low-Voltage Applications
Keywords: Low-dropout Regulator, Bandgap Voltage Reference, Point-of-load (POL)
Power supplies and voltage references are key elements in electronics systems. As efficiency is particularly critical in high-temperature environments (small self-heating margin together with high price of batteries), more and more systems use point-of-load (POL) architectures. With multi output POL DC-DC converters, line and load regulation are usually quite poor due to transformer’s leakage inductors together with the fact that there is not a feedback network on each output voltage. It is then often required to add a low dropout linear regulator after each POL output in order to obtain a clean and stable regulated voltage without losing too much efficiency. If versatile and efficient high temperature PWM controllers are available for implementing DC-DC converters, so far there was no true low-dropout, high current linear regulators available. This is even truer for output voltages bellow 1.2V. In this paper we present two innovative devices with guaranteed operation from -65C to +230C for systems with reduced supply voltages. These devices are manufactured on an extremely robust high-temperature SOI CMOS process. The first part of this paper presents an original implementation of such a monolithic low dropout regulator (XTR70010), able to deliver up to 1A at 230C with only 0.5V of dropout (1.5A with 1V dropout). This new voltage regulator can operate with input voltages from 2.8V to 5.5V while sourcing a high output current level. The regulator presents several selectable discrete output voltage values ranging from 0.5V up to 3.6V in steps of 100mV. Also, an external resistor divider can be used for a customer selected output voltage. The circuit integrates complex analog and digital control blocks providing state of the arts features, such as UVLO protection, chip enable control, soft start-up and shut-down, hiccup short-circuit protection, customer selectable thermal shut-down, input power supply protection (in case of poorly bypassed input), output overshoot remover and stability over an extremely wide range of load capacitances. The circuit offers a fair 4% absolute accuracy and is guaranteed latch-up free. The second part of this paper presents an advanced high-temperature, low-power, digitally trimmable voltage reference (XTR75020). Thanks to a custom, 1-wire serial interface, the absolute precision and the temperature coefficient can be adjusted in order to obtain an accuracy better than 0.25% with a temperature coefficient bellow +-20ppm/C. On-chip trimming OTP memory coupled with chopping techniques make the circuit extremely accurate and almost insensitive to internal offset drifts over time and temperature. Besides its precision, the circuit presents a class AB output buffer able to source or sink up to 5mA while most existing products can only source current. The new voltage reference is stable on any load capacitance up to 50µF, latch-up free and it can be disabled by a shutdown pin. The input voltage range is 2.8V up to 5.5V while several selectable discrete output voltages are available between 0.5V and 4V. The source and sink short circuit current always remains bellow 25mA. The quiescent current consumption is 300uA typical at 230C while the standby current is, in all cases, under 20uA.
Yoann Duse,
X-REL Semiconductor
Grenoble, Isère

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