1. Field of the Invention
This invention relates to an in-vehicle electronic control device which is a constant voltage control device built into an in-vehicle electronic control device such as an engine control device and a transmission control device, the in-vehicle electronic control device being so improved as to reduce a fluctuation error in output voltage of a constant voltage control circuit generating a predetermined constant voltage output by the use of power supplied from an in-vehicle battery.
2. Description of the Related Art
In the in-vehicle electronic control device, it is important to enhance a constant voltage control accuracy of the built-in constant voltage power source circuit in view of, for example, improvement in AD conversion accuracy in a multi-channel AD converter and improvements in generation accuracy of various comparison reference voltages.
However, though an individual fluctuation of each component parts is inevitable, an expensive constant voltage power source circuit will undesirably be required for obtaining a very high accuracy constant voltage output.
In order to avoid such problem, the constant voltage control accuracy has been improved by using a constant voltage power source device having a constant voltage control accuracy lower than an expectation value and adding an auxiliary unit for correcting a reduction in constant voltage control accuracy.
For instance, Patent Document 1: Japanese Patent Publication 2002-366238 “Circuit Device and method for Setting Adjustment Data of Circuit Device” (refer to paragraph [0009] and FIG. 5) describes that in a constant voltage generation circuit included in a semiconductor sensor or an engine control unit (ECU) for a vehicle, a reference voltage VBGR which is an output voltage of a reference voltage generation circuit having a band gap regulator is amplified by an operational amplifier to obtain a predetermined constant voltage output Vcc, and, at the same time, a predetermined constant voltage output Vcc is obtained by writing adjustment data to an EPROM memory in order to correct an individual fluctuation in reference voltage VBGR and by changing a gain of the operational amplifier by the adjustment data.
In the invention disclosed in Patent Document 1, functions not only improving the constant voltage control accuracy but also adjusting a threshold value of a reset circuit in tandem with the adjustment data are added to the unit.
Also, Patent Document 2: Japanese Patent Publication 09-297623 “Voltage/Current Regulator Circuit” (refer to FIG. 3 and Abstract) describes that a resistance circuit network deciding a resistance value by the use of ROM data is included as a resistance circuit for deciding a differential amplification ratio in a constant voltage regulator circuit which is used for a temperature compensation oscillator, for example, and outputs signals subjected to differential amplification between a reference voltage source and a detected voltage, and fine regulation of a stabilized voltage is achieved by the use of the ROM data.