Design of a high-voltage three-channel voltage regulator for automotive applications
The paper presents the principles of designing a three-channel voltage regulator. Modern technologies for intelligent power management allow of implementing complex functionality within a single circuit. One of the possible applications of power management systems is their use as voltage regulators. Here, an important role is played by such system parameters as the generated voltage levels and / or currents, real-time temperature monitoring and various types of errors that such a key reports to the central controller in real time. The minimum switching time of such a regulator reduces likelihood of an error associated with noise from the power supply circuits of the microcircuit. Intelligent power management technologies allow the development of a variety of specialized systems such as anti-lock brakes, airbag control or engine management in car electronics. As well as the systems similar in structure in the fields of industrial electronics, telecommunications and data processing. Currently available systems allow to manage power and external systems and analyze systems for errors or hazardous conditions. The proposed solution allows to provide a stable output voltage of 5V in a wide range of input voltages from 5.5 to 45V, with an output current of up to 450mA in the main channel and up to 150mA and 50mA in the auxiliary ones. The paper describes the main functions of the design, such as the function of limiting the output current, protection against reverse polarity, temperature protection, the function of limiting the excess of the output voltage, as well as the digital function of the built-in "watch dog" timer intended for connecting the design to a microcontroller unit.
The integrated circuits for secondary power supplies [1, 2], namely linear voltage regulators that form a stable voltage at the output with extended functionality and interface with the main types of modern microcontrollers (microprocessors) make the basis of the intelligent power management systems.
Intelligent integrated circuits for power management are becoming more common in various branches of microelectronics, especially in those that require system integration. Today’s intelligent power management technologies make it possible to implement complex functionality within a single circuit, providing increased reliability while saving space and weight. Applications for such systems include:
automotive electronics, as its increasing demands for safety and comfort are leading to an increase in the number of electronic components used in modern vehicles;
industrial electronics, namely, intelligent control systems for machines and mechanisms; this includes the control of electric motors of various capacities;
telecommunication systems, where it is necessary to implement systems that combine transmission of high-power signals with reception of signals at milli-watt level.
The developed IC is designed to generate power module supply voltages and will be used in control systems of drives and engines of different power and different types, such as DC commutator,brushless and inverter-fed motors, synchronous and asynchronous AC motors, stepper motors; motors can be one, two and three-phase. Due to their versatility, the above mentioned systems can be used almost anywhere where electric motors are used.
THREE-CHANNEL VOLTAGE REGULATOR ARCHITECTURE
The three-channel voltage regulator (Fig.1) consists of the following units:
- the pre-stabiliser is responsible for creating the start-up condition for the main units of the system;
- the reference voltage source forms the thermostable system reference voltage;
- the source of reference currents forms stable operating currents;
- buffer amplifiers that form part of the local voltage regulators;
- temperature sensor forms the signal when the crystal temperature limit is exceeded;
- reference voltage generator generates stable frequency of 10 kHz;
- 1st "reset" signal generator generates microcontroller reset signal;
- the 2nd "reset" signal generator generates the reset signal of the internal units of the system;
- the output power limitation unit performs the function of protection against excessive supply voltage and limitation of power allocated in the enclosure;
- local regulators and short-circuit current regulator.
The pre-stabiliser unit is designed to create the conditions for starting the main functional blocks to ensure accurate performance of the overall system for a wide range of supply voltages (5 to 40 V). These blocks include a reference voltage source and a reference current source. Presence of a pre-stabiliser provides a high supply voltage suppression coefficient and, consequently, a high accuracy of the reference voltage and current values. This architecture enables to use MOS-transistors with small and low operating drain-source voltages in the main circuitry, which guarantees a high accuracy of the output parameters of the reference voltage source (RVS) and the source of reference currents.
The basic circuit diagram of the pre-stabiliser unit is shown in Fig.2.
OUTPUT POWER LIMITER
schematic diagrams of the in-line switch and the power dissipation limiter (current limiter) are shown in fig.3, 4, respectively. A transmission gate is switched in the inverse mode in order to eliminate current in the reverse polarity mode of the supply voltage.
Of course, it is practical to connect the same transistor in direct connection. However, in this case there would be double voltage drop across the key with a total load current of 0.6 A and it would be difficult to meet the output voltage rating requirement. In active mode the minimum switch resistance is provided by the current limiting unit generating a negative voltage (approx. 5 V) relative to the drain at the control input of the switch. In sleep mode, when this current is not present, minimum consumption will be achieved by removing the load from the stabilisers.
The current-limiting unit has several functions:
- protection of the divider against polarity reversal of the supply voltage;
- creation of the key control current;
- over-voltage protection and power dissipation limitation.
Several mode currents are drawn from the start circuit, in particular the drain current flowing to the gate of the pass-through keys provides key control and protection of the divider against polarity reversal.
The other two functions are performed by:
a comparator that provides over-voltage protection;
two voltage-to-current converters that perform power dissipation limitation).
A schematic diagram of the thermal protection unit is shown in Fig.5. Here, the voltage-to-current converter generates an output current, the nature of which is determined by R1 resistor. The circuit has two operating modes: working and test.
Under typical operating conditions, a high level at the "work" node in the amplifier feedback, we set the block trip at 160 degrees and the value of the hysteresis. The temperature of 160 degrees is outside the temperature range of the chip, which makes thermal protection control undesirable.
In test mode, the unit is actuated at 100 degrees Celsius, which is within the temperature range of the chip and reduces the cost of monitoring the performance of the unit. Trim the unit in test mode by setting triggering at 100 degrees. In this case, in the working mode, it is necessary to set the block actuation at 160 degrees.
LOCAL AND SHORT-CIRCUIT CURRENT REGULATORS
Figure 6 shows a short-circuit current regulator.
To adjust the short-circuit current and output voltage rating, a sensitive single transistor M29 is included in parallel with the output transistor M28.
In short-circuit mode, when the regulator output voltage is near zero, the current-limiting amplifier is enabled. This activates the internal feedback of the amplifier, with a 1.25 V reference voltage applied to the non-inverting input of the amplifier.
Feedback balances the voltages at the amplifier inputs. By changing the rating of the resistors R32 and R24, we control the short-circuit current. So, by decreasing the resistor rating, more current is required from the sensitive transistor, and, hence, from the output transistor, to balance the voltages at the amplifier inputs. Thus, by pumping current through the "ireg" pin into the resistors R32 and R24, we reduce the short-circuit current. The regulators "Q2" and "Q3" are made according to a similar circuit and differ only in the output transistors.
If there is no short circuit, the "amp_ilim_p" is de-energised and external feedback is activated, freeing up internal resources to achieve high accuracy.
The circuit for linear short-circuit current reduction above 22 V supply voltage operates as follows: the output current of the upper voltage-current converter is monitored by a divider and varies linearly with the change in supply voltage. The output current of the lower voltage-current converter is constant.
The output current of the upper inverter continues to increase, while that of the lower inverter remains the same, allowing the difference in these currents to be transferred to the output.
The output current in this case increases linearly with increasing supply voltage.
This current is then fed to the regulator block via the "ireg" pin, increasing the voltage at the inverting input of the "amp_ilim_p" amplifier, which results in a reduction of the short-circuit current. This current can be controlled by trimming, which is carried out by the short-circuit current regulator block.
REFERENCE VOLTAGE SOURCE UNIT
The schematic diagram of the reference voltage source unit, which no automatic control system can do without, is shown in Fig.7 [3, 4] (RVS). It acts as a unit of measurement in the system, the use of which ensures static accuracy of the product and determines the accuracy of output voltages of local regulators, acting as a reference element in local feedback circuits.
The "core" of the circuit is represented by the substrate PNP transistors (Q1, Q2), resistor R1 and transistors M1, M2. Moreover, transistor Q2 represents N transistors of Q1. At the same time a voltage is allocated to resistor R1:
V = (k•T/q) • ln(N)/R1 (1),
where k is Boltzmann constant, q is the electron charge.
The circuit includes a trimmer which receives the drain current of the M5 transistor, which is a part of the core transistor current.
REFERENCE CURRENT SOURCE UNIT
As in the previous unit, the transistors M15 and M18 represent the start circuit. The "core" of the circuit is represented by transistors: M46, M47, M33, Q2, Q3 and resistors: R3, R2, R14, R15. The emitter current density of transistor Q2, in this circuit, is eight times less than the emitter current density of transistor Q3 (Fig.8).
The collector current of transistor Q2 will have a positive temperature coefficient, and a corresponding voltage will be formed in resistor R3 according to expression (1). With the rating of resistor R3 we control the amount of current with a positive temperature coefficient. The sum of the resistors R2, R14 and R15, which are connected in parallel to the emitter base junction of the bipolar transistors, we control the current with a negative temperature coefficient. By adding these currents on the M46 transistor and adjusting one of the currents, we achieve a temperature independent current at the output.
The circuit generates seven currents of 10 µA and one current for the oscillator (about 1.2 µA). The currents are trimmed in the same way as the RVS unit.
The topology  of the three-channel voltage regulator is shown in Fig.9.
The numbers indicate the following blocks:
a buffer amplifier;
source of reference voltage;
source of reference currents;
reference voltage generator;
2nd "reset" signal generator;
1st "reset" signal generator;
short-circuit current regulator;
SIMULATION RESULTS FOR A THREE-CHANNEL VOLTAGE REGULATOR
Plots of the output voltage of the reference voltage source and of each regulator are shown in Fig.11 and Fig.12, respectively.
The output results are shown in Fig.11. Based on these results, it can be said that the scatter of the output voltage by temperature at each output is 0.09 mV/°C.
This chip is intended to be used in two case styles: PSOP and SOIC, which are shown in Fig.12.
As a result of designing a three-channel voltage regulator the following results have been obtained: a schematic circuit diagram of the microcircuit has been developed, circuit modeling with the use of technological libraries and specialized CAD tools has been performed, the topology of the integrated circuit has been developed and verified. Main electrical characteristics are determined: output voltage, maximum output current, and open state key resistance. The measuring equipment was developed and laboratory measurements of key parameters were carried out. In future, additional laboratory measurements and testing of the chip are planned to determine additional parameters of the IC and enter the data into the specification. ■
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.