This paper presents a novel circuit implementation for overcurrent protection of low-dropout voltage regulators, that is able to limit the maximum current the regulator can source into the load to a value set by the user and to keep the... more
This paper presents a novel circuit implementation for overcurrent protection of low-dropout voltage regulators, that is able to limit the maximum current the regulator can source into the load to a value set by the user and to keep the current limit value fairly independent of process variation and output voltage, as well as maintaining its temperature drift over the wide temperature range of −50°C to +185°C to below 15%. This is achieved by using an open loop Widlar bandgap structure supplied by an additional current branch, placed in parallel with the power transistor. Design equations are presented in the paper along with electro-thermal simulations that identify the hot spots of the power transistor, thus optimizing the placement of the sense transistor and improving the current sensing accuracy. The proposed circuit is implemented in a standard bipolar junction transistor process. Measurement results — including thermal test scenarios are in good correlation with simulations, thus validating the design.
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This paper presents an over-temperature protection (OTP) circuit for a DC-DC converter based on switching capacitors (SC DC-DC). The circuit was designed by using a two-step approach that encompasses running both electrical and... more
This paper presents an over-temperature protection (OTP) circuit for a DC-DC converter based on switching capacitors (SC DC-DC). The circuit was designed by using a two-step approach that encompasses running both electrical and electro-thermal simulations. The die temperature distribution was analyzed for two critical operational scenarios in order to identify the worst case and to provide design data for implementing a robust and precise OTP. Finally, a design example of a SC DC-DC with OTP is presented in some detail, complete with the key electrical and electro-thermal simulation results.
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This paper presents an over-temperature protection (OTP) circuit for a DCDC converter based on switching capacitors (SC DC-DC). A two-steps design methodology was employed: a first-pass circuit was obtained by using standard,... more
This paper presents an over-temperature protection (OTP) circuit for a DCDC converter based on switching capacitors (SC DC-DC). A two-steps design methodology was employed: a first-pass circuit was obtained by using standard, electrical-only simulations; next, electro-thermal simulations were employed to ascertain the best location of the thermal sensor and the resulting thermal coupling, thus allowing for the fine-tuning of the final circuit. The die temperature distribution was analyzed for two critical operational scenarios in order to identify the worst case and to provide design data for implementing a robust and precise OTP. The key electrical and electro-thermal simulation results are presented in some detail. Finally, results of measurement performed on the actual silicon are presented, to validate the design. Key-words: Over-temperature protection; switched-capacitor DC-DC converter; controlled charging current, thermal shutdown; electro-thermal simulations.
This paper presents an intuitive analysis of a class of conditionally stable feedback circuits, that are stable although the Bode stability criteria indicates otherwise: at the frequencies their loop gain phase characteristics first reach... more
This paper presents an intuitive analysis of a class of conditionally stable feedback circuits, that are stable although the Bode stability criteria indicates otherwise: at the frequencies their loop gain phase characteristics first reach -180°, the magnitudes of their magnitude characteristics are far larger than unity. An easy-to-use stability criterion is introduced by means of two circuit examples. Only the usual loop gain Bode plots are required to apply this criterion, but it suits only conditionally stable systems with no right-hand plane (RHP) poles in the open loop transfer function, T(s), and no integrators. A separate, three-step method for assessing the stability of feedback circuits with RHP poles and integrators is also proposed. It applies to all conditionally stable circuits and involves extracting the poles and zeros of T(s) and plotting the corresponding Nyquist contour.
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ICs designed for automotive applications should withstand accidental reverse polarity caused by misconnection of their supply lines to the car battery. The reverse protection circuitry should avoid damages to both the IC and the system... more
ICs designed for automotive applications should withstand accidental reverse polarity caused by misconnection of their supply lines to the car battery. The reverse protection circuitry should avoid damages to both the IC and the system the IC is connected to. In particular, a large power dissipation while in reverse polarity situation is to be avoided. A simple solution is to insert diodes between the supply lines and the IC supply pins but this cannot be applied to linear low dropout regulators (LDOs)This paper presents two reverse polarity protection solutions for LDOs with NMOS power transistors. Starting from a circuit based on bipolar transistors, the proposed solutions can be implemented in low-cost CMOS processes. One of them also requires far less die-area Simulation results presented in the paper validate both proposals.
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This paper presents novel circuitry for protection of the power transistor in LDOs with adjustable output voltage implemented in BJT technologies. First, an improvement is proposed to ...
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This paper presents several design options for implementing a thermal shutdown circuit with hysteretic characteristic, which has two special features: a programmable activation tempera ...
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This paper presents a design methodology based on electro-thermal simulations for the over-temperature protection (OTP) of low drop-out voltage regulators (LDO). The OTP monitors the die temperature developed within the LDO and shuts down... more
This paper presents a design methodology based on electro-thermal simulations for the over-temperature protection (OTP) of low drop-out voltage regulators (LDO). The OTP monitors the die temperature developed within the LDO and shuts down the circuit when the temperature reaches a set maximum level (the OTP trigger point). The proposed methodology involves running iteratively electrical, thermal and electro-thermal simulations. It addresses two major issues: first, it allows the designer to identify the suitable location of the OTP sensor by considering the temperature distribution within the LDO's power-stage. Second, the OTP trigger point can be set accurately taking into account coupled electro-thermal phenomena, so that the circuit is shut down when any section of the die reaches the maximum allowable temperature. The proposed methodology is validated by measurements performed on an LDO designed using it.
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This paper compares the performance of four popular design environments for analog and mixed-signal applications - Virtuoso from Cadence Inc., SIMetrix/SIMPLIS, Simulink and CppSim - when used for system level analysis of a standard... more
This paper compares the performance of four popular design environments for analog and mixed-signal applications - Virtuoso from Cadence Inc., SIMetrix/SIMPLIS, Simulink and CppSim - when used for system level analysis of a standard switched capacitor DC-DC converter. Virtuoso is the most expensive of the four but it has the best user interface and its Spice-level circuit simulators provide very good accuracy. Also, it allows complete top-down design, from system- to circuit-level within the same environment. However, it may not be best suited for first-pass system-level analysis of switching circuits such as DC-DC converters due to its long simulation time and convergence issues. Numerical solvers such as MATLAB - Simulink and CppSim represent functional blocks by input-state-output relationships, thus avoiding the solving of large sets of simultaneous equations. This reduces dramatically the simulation time at the expense of poorer accuracy. SIMetrix/SIMPLIS converts non-linear models to a piecewise linear straight-line model achieving a fast simulation time for switching circuits. For a fair comparison, the same circuit was analyzed under the same conditions by using the four design environments; the trade-offs between cost, accuracy and simulation time are highlighted.
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This paper presents novel circuit solutions for two issues related to the Enable control of low-dropout (LDO) voltage regulators: setting precise voltage thresholds for the ON/OFF states of the LDO and ensuring that in the OFF state the... more
This paper presents novel circuit solutions for two issues related to the Enable control of low-dropout (LDO) voltage regulators: setting precise voltage thresholds for the ON/OFF states of the LDO and ensuring that in the OFF state the LDO output is not affected by fast variations of the supply voltage. First, an Enable circuit with hysteresis and temperature compensated thresholds is described: the accuracy of its threshold voltages - including their low temperature coefficients - are predicted by analytical analysis and validated by measurements performed on a silicon implementation. Second, a simple yet effective comparator is proposed, able to significantly reduce the effect the supply voltage variations have on the output voltage when the regulator is in OFF state. Simulation results show that, when the supply voltage varies from 0 to 28V in 28μs, the overshoot of the output voltage is reduced from 5.5V to under 200mV, that is by a factor of 35.