Application of ME2175 Chip in Preheating Thermometers

Ear thermometers have become common household medical devices, especially for infants and young children. Accuracy and convenience are the key factors in improving these products. One significant challenge faced by traditional ear thermometers is the cold shock effect when the probe enters the ear, which can lead to inaccurate readings. The ME2175 chip, applied in preheating ear thermometers, provides a solution to this problem by using sensor preheating technology to ensure more accurate measurements.

Working Principle of Preheating Ear Thermometers

The preheating ear thermometer uses the ME2175 chip to step up the voltage from two AA batteries to 3.3V, powering the heating element. This preheats the probe to a temperature close to that of the human body before it enters the ear. Unlike traditional ear thermometers, which are affected by the temperature of the environment, the preheating ear thermometer reduces the cold shock impact and ensures accurate temperature readings through the use of thermopile sensor preheating technology.

Advantages of the ME2175 Chip in Application

1. High Efficiency: The ME2175 is capable of stepping up from 3V to 3.3V with an efficiency of up to 91.2% when driving a 1A load. The maximum load current it can handle is 1.7A. This high efficiency minimizes energy loss and extends battery life.

2. Current Limiting Protection: The ME2175 features current limiting protection. When the peak current exceeds 3A, the chip automatically limits the current to prevent damage to the circuit.

3. PWM/PFM Switching: The ME2175 can automatically switch between Pulse Width Modulation (PWM) and Pulse Frequency Modulation (PFM) modes depending on the load. In high-load conditions, the chip operates in PWM mode, producing low output ripple. In low-load conditions, the chip switches to PFM mode, which reduces current loss and improves efficiency.

Design Considerations for Application

1. Inductor Selection: In DC-DC boost converters, the inductor value affects both the peak current and the output stability. A smaller inductance results in higher peak current and increased output current, but can also increase ripple current. A larger inductance helps reduce ripple and improves stability. It is essential that the inductor has a low DC resistance and high current capacity to avoid reaching magnetic saturation during operation.

2. Capacitor Selection: The output current in a boost converter is discontinuous, and if the output capacitance is too small, it can cause high output ripple. The capacitor should have good frequency characteristics. ME2175 recommends a 44µF output capacitor. For mitigating voltage overshoot during no-load startup, a 100µF electrolytic capacitor should be added at the Vout terminal to minimize the overshoot.

3. PCB Design Considerations: To reduce electromagnetic interference (EMI) caused by high-frequency switching, it is recommended to keep the traces from the chip to external components as short as possible, especially for the LX (inductor) trace. Using thicker PCB copper and adding additional heat dissipation holes will help enhance both the thermal management and overall efficiency of the system.

Read more: STMicroelectronics' next generation of smart wearable medical devices

Conclusion

The ME2175 chip in preheating ear thermometers plays a crucial role in improving measurement accuracy and extending battery life. Its high efficiency, current limiting protection, and automatic PWM/PFM switching ensure reliable performance in demanding applications. As technology advances, preheating ear thermometers powered by the ME2175 chip offer consumers an enhanced and more accurate measurement experience, addressing key challenges in medical devices.