A high temperature (>200 °C), quad-output, buck type switched-mode power supply (SMPS) IC capable of operating over a wide input supply range of 6 V to 15 V is described. The IC is a compact power supply solution for multi-voltage microprocessors, sensors, and actuators. The SMPS topology is a 112 kHz fixed-frequency, synchronous buck converter with slope compensation. A novel internal feedback design enables the output voltages to be pin-programmed to one of three common supply voltages—5 V, 3.3 V, or 1.8 V—while an external resistor divider can also be used for arbitrary voltage programming. Integrated power supply output MOSFET switches minimize the external part count and synchronous rectification reduces power dissipation and improves current capacity. The IC was fabricated in a conventional, low-cost, 0.5 μm bulk CMOS foundry process. Patented circuit design techniques allow the IC to operate in excess of 200 °C and circuit operation was demonstrated at ambient temperatures up to 225 °C. The foundry process is optimized for 5 V applications, however, the IC accepts input voltages up to 15 V and can produce outputs up to 10 V by utilizing extended drain single- and double-sided NMOS and PMOS transistors for the linear regulator pass transistor, error amplifier, and SMPS switches. The high-side FETs are controlled through capacitive coupled level shift circuits to ensure the gate-oxide voltage limits are not exceeded while still maintaining fast signal transitions. The IC also includes a tunable, 25 MHz monolithic oscillator that is programmable over a SPI serial interface. The oscillator bias current is comprised of a programmable constant-gm bias current and a programmable PTAT bias current. The programmability can be used to set the oscillation frequency, but can also be used together with a calibration curve on a microcontroller to achieve a more stable oscillation frequency over temperature. The output current of the quad SMPS was limited to 70 mA by a lower than expected saturation current of the extended-drain PMOS switch devices. The system showed good line regulation (<0.1%) and 50% load step response stability (+/− 100 mV) at a nominal output current of 50 mA when tested at 200 °C ambient.
Stacked Buck Converter: Current Ripple Elimination Effect and Transient Response
