图5。带SMBus 功能的PWM 输出电路图
Again, the PWM mode needs to be written as the POR default in EEPROM. Then for PWM operation the SCL line can be high impedance, forced high, or even not connected. The pull-up resistor R1 will ensure there is a high level on the SCL pin and the PWM POR default will be active. SMBus is still available (for example – for further reconfiguration of the MLX90614, or sleep mode power management) as there are pull-up resistors on the SMBus lines anyway.
PWM can be configured as open drain NMOS or a push-pull output. In the case of open drain external pull-up will be needed. This allows cheap level conversion to lower logic high voltage. Internal pull-ups present in many MCUs can also be used.
4．热告警/自动调温器
图6。MLX90614热告警/自动调温器应用电路图
The MLX90614 can be configured in EEPROM to operate as a thermal relay. A non contact freezing or boiling prevention with 1 mA quiescent current can be built with two components only – the MLX90614 and a capacitor. The PWM/SDA pin can be programmed as a push-pull or open drain NMOS, which can trigger an external device, such as a relay (refer to electrical specifications for load capability), buzzer, RF transmitter or a LED. This feature allows very simple thermostats to be built without the need of any MCU and zero design overhead required for firmware development. In conjunction with a MCU, this function can operate as a system alert that wakes up the MCU. Both object temperature and sensor die temperature can also be read in this configuration.
5．高压电源应用电路
As a standard, the module MLX90614Axx works with a supply voltage of 5Volt. In addition, thanks to the integrated internal reference regulator available at pin SCL/Vz, this module can easily be powered from higher voltage source (like VDD=8…16V). Only a few external components as depicted in the diagram below are required to achieve this.
图7。12V电源应用电路图
With the second (synthesized Zener diode) function of the SCL/Vz pin used, the 2-wire interface function is available only if the voltage regulator is overdriven (5V regulated power is forced to Vdd pin).
MLX90614的评估板EVB90614
图8。评估板EVB90614外形图
The EVB90614 is designed to support MLX90614 infrared thermometer modules.
The communication between PC and the evaluation board is accomplished by USB.
The Demonstration Kit contains the following items:
1. FS USB demonstration board, pre-programmed with USB bootloader and demonstration firmware.
2. A standard USB cable for use in communicating with the board.
3. 1 pc. MLX90614AAA (single zone 5V)
4. 1 pc. MLX90614BAA (single zone 3V)
5. CD-ROM, containing the USB HID driver and EVB90614 software
The EVB90614 is designed to allow OEMs to configure the MLX 90614 IR thermometer for virtually any application quickly. OEMs can quickly experiment with temperature ranges, optics, etc. to find the best IR configuration to meet the application needs. Once the best configuration is established, low volume OEMs can easily configure IR modules
for their own use. For high volume OEMs, Melexis can supply special configured
modules, ready to install into the customer’s application. Please contact IR Sales at
Melexis for quotations.
The EVB90614 allows engineers to customize the MLX90614 for high accuracy IR
measurements in an R&D or Laboratory setting.
图9。评估板EVB90614电路图
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本文关键字：测量 红外温度 电工文摘，电工技术 - 电工文摘
