Low power consumption, is an extremely important concept in all things interconnection. Most of the Internet of Things nodes need to use battery power, and only correctly measure the power consumption of the wireless module, to accurately estimate how large batteries need to be used in the end of 5 years. This article will explain the detailed measurement method for you.
In many applications in the Internet of Things, the terminal device is usually battery powered, and the amount of power available is limited. Since there is self-discharge, the actual use is only about 70% of the nominal power, such as a common CR2032 button battery, and the battery nominal capacity is 200mAh, and only 140mAh can be used.
Since the battery's power is so limited, it is very important to reduce product power consumption! Let's first understand the means of commonly used measurement power consumption, only the methods of these measurement power consumption can be made to optimize product power consumption.
First, power consumption measurement
The power consumption test of the wireless module is mainly measured, and there are two different tests of static current and dynamic current. When the module is in a sleep or standby, the current does not change, maintain a stationary value, we call it static current. At this time, we can use a traditional multimeter to measure, and you can get the values you need to measure in the power pins, as shown in Figure 1.
Figure 10 million Test
When the transmission current of the module is normal, since the time required for the signal emission is very short, the entire current is in a changing state, we call the dynamic current. The multimeter response time is slow, it is difficult to capture the changed current, so you can't use the multimeter measurement. For the change current, you need to use an oscilloscope and current probe to measure, and the measurement results are shown in Figure 2.
Figure 2 Current probe measurement results
Second, the battery use timecore calculation
Wireless modules often have two working modes, operating modes, sleep modes, as shown in Figure 3 below.
Figure 3 average current
The above data is based on our company's LM400TU product. According to the above figure, the transmission interval between the two sending packets is 1000ms, and the average current is calculated:
That is, the average current in 1 second is approximately 2.4mA, and if the CR2032 is powered, it is ideally for approximately 83 hours, about 3.5 days. If we extend the working time is 1 hour? Similarly, it can be calculated by the above formula, and the average current of 1 hour is only 1.67uA. The same section of the CR2032 battery can support equipment for 119760 hours, about 13 years! It is seen from the above two examples that increase the time interval between the sending packets, extend the sleep time, and reduce the power consumption of the whole machine, so that the equipment can work longer. This is also why the products in the wireless meter reading industry are very long because they only send data every day.
Third, common power consumption problems and reasons
In order to ensure the low power consumption of the product, in addition to increasing the package interval, it is to reduce the current consumption of the product itself, which is iWork and ISLEP mentioned above. Under normal circumstances, these two values should be consistent with the chip data manual, but if the user is improper, there may be problems. When we test the emission current of the module, we found that the installation antenna has a great impact on the test results. When the antenna measurement is measured, a product current is 120mA, but if the antenna is removed, the test current is raised to nearly 150mA. In this case, the power consumption is mainly mounted by the module radio frequency, causing an exception in the internal PA working. Therefore, we recommend that customers must carry test when assessing the wireless module.
In the previous calculation, when the transmission interval is getting longer, the working current duty cycle is getting smaller and smaller, and the factor affecting the power consumption of the whole machine is isleep. The smaller Isleep, the longer the product life is. This value is generally close to the chip data manual, but we often encounter the sleeping current of the customer feedback test, why?
This problem is often caused by the configuration of the MCU, and the general MCU single IO downs can reach the MA level. In other words, if you accidentally miss or miss the status of an IO port, it is possible to destroy the previous low-power design. The following is a small experiment with a product as an example to see how much this problem has.
Figure 4 Low Power IO Configuration Test Results of Product A
Figure 5 IO configuration improper test results
During the test of Figures 4 and 5, the test object is the same product, which is equally configured to sleep mode, which can be clearly seen that the test results are different. In Fig. 4, all IO is configured to input pull-down or pull-up, the test current is only 4.9ua, and in Fig. 5, only two IO are configured to float input, and the test result is 86.1ua.
If the operating current and the time length of Fig. 3 are constant, the transmission interval is 1 hour, which is brought into different sleep current calculations. According to the results of Fig. 4, the average current of an hour is 5.57ua, and it is 86.77ua according to Fig. 5, which is about 16 times the phase difference. Also using a 200mAH CR2032 battery, the product can be used in accordance with the configuration of Figure 4, and the normal working time is about 4 years, and according to Figure 5, this result is only about 3 months!
As can be seen from the above example, the following design principles should be followed as much as possible to extend the use of wireless modules:
1. Under the conditions that meet the customer application requirements, the sending package interval as much as possible, reducing the working current during the work cycle;
2, must correctly configure the MCU IO status, different manufacturers' MCU may have different configurations, detailed reference materials.
Reprinted from Verid Electronic Market Network.
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