Part5 CMOS Operational Amplifier for Automotive Use S-19630AB, supporting fuel-efficient and comfortable driving

TechanaLye12/10/2018
Techanalye Co.,Ltd.

This time, I introduce the S-19630AB, a Zero-drift Operational Amplifier for Automotive Use which is launched on Sep. 7, 2018. A zero-drift operational amplifier always monitors its offset voltage to automatically adjust it to zero. When the difference between the plus and minus input pins is 0 volts, there is an error voltage present at its output. The offset voltage is an input corresponding value to make the output voltage zero. The S-19630AB is featuring low offset voltage of 50uV max., low offset voltage drift of 25nV/°C, current consumption of 250uA and is capable of operating at 125°C. Figure 1 is an appearance and main features of the S-19630AB.

Figure 1 Appearance and main features of the S-19630AB
Figure 1 Appearance and main features of the S-19630AB
Table 1 Main features of S-19630AB
Operation power supply voltage range 4.0~36.0V
Input offset voltage ±10μV typ.
±50μV max.
Input offset voltage drift ±25nV/℃ typ.
±120nV/℃ max.
(VDD=30.0V)
Operation temperature range Ta=-40~+125℃
(Tj=+150℃ max.)

How and where the operational amplifier is used in the automobiles and what it can do? Let us consider a transmission as an example. In short, a transmission is a component that transmits power from the engine to the wheels while changing the rotation speed and direction. As shown in Figure 2, power is transmitted from the engine through the clutch to the wheels by mean of a hydraulic pressure control circuit which adjust the hydraulic pressure based on rotation information and shift gears. One of the parts in the hydraulic pressure control circuit for changing the flow of the hydraulic pressure circuit is a solenoid valve. 

Figure 2 Role of the transmission
Figure 2 Role of the transmission

Figure 3 shows the solenoid valve and its peripheral circuit. When a solenoid current set value is entered, the circuit operates to take the solenoid current which is same as the value. If the solenoid current is detected with high accuracy, the hydraulic control in the solenoid valve is performed with high precision, and mechanical behavior of a clutch and other parts can be freely controlled. In other words, it provides the ideal gear changing and supports comfortable and fuel-efficient driving.

Figure 3 Solenoid valve and its peripheral circuit
Figure 3 Solenoid valve and its peripheral circuit

By the way, a voltage across the solenoid current detection resistor is small (tens of millivolt level) and it requires a high-precision amplifier. Traditionally, bipolar operational amplifiers which have relatively lower offset voltages were used but higher precision operations are possible by using the S-19630AB which is introduced in the beginning. The left of the Figure 4 shows the offset voltage comparison between the S-19630AB and a bipolar amplifier. The right figure is the offset voltage drift comparison including a bipolar amplifier stored the offset voltage in a memory in the shipment process and corrected. Both show the performance of the S-19630AB has improved 100 times better than existing bipolar amplifier. That is, by using the S-19630AB, a conventional problem of the offset voltages caused by a power supply voltage change and a temperature change can be reduced and you can control an automobile transmission with higher accuracy. Furthermore, a calibration which has done with a bipolar amplifier and a memory in the past is no longer needed. Therefore, no work needed to correct, number of components can be reduced and BOM area also be reduced.

Figure 4 Performance comparison between S-19630AB and bipolar amplifier
Figure 4 Performance comparison between S-19630AB and bipolar amplifier

There are still other parts that solenoid valve is used in a vehicle. And beside the above, the S-19630AB has additional features which are not included in the existing CMOS operational amplifier. In the next article, let us consider another use case of the S-19630AB in the field of automobiles and its future plan.

Next: S-19630AB and beyond,
future plan of the automotive CMOS operational amplifier

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