Do you know how important low Iq LDO is for wearable devices to achieve long battery life
Time:2022-10-30
Views:1530
Using a linear low dropout voltage regulator (LDO) with low quiescent current (Iq) can prolong the battery life of wearable devices and wireless Internet of Things (IoT) devices, but there are performance tradeoffs, including transient response, noise performance and output power range. In addition, quiescent current is sometimes confused with turn off or disable current (Id). These are two different currents and need to be balanced between them. Of course, if the whole system design is not optimized for low power consumption operation, it is useless to simply optimize the IQ and Id.
In this paper, we will distinguish between Iq and Id, and briefly discuss the impact of each current on power dissipation. Then, we will review several performance tradeoffs, and finally introduce some typical LDOs and demonstration boards of Microchip and Texas Instruments.
Difference between static and shutdown
Ready is the difference between static and shutdown. In static state, the system is in low power consumption and active state, and can be put into operation at any time. During shutdown (sometimes referred to as disable mode), the system is in a sleep state and cannot run immediately. This difference is particularly important in battery powered systems. For example, the wireless lock is in standby mode for a long time (usually>99% of the time), and the difference between standby and activation current consumption is large (Figure 1). The quiescent current can be used to calculate the power under light load, while the turn off current can be used to determine the long-term life of the battery.
Figure 1: For many wireless IoT devices such as wireless locks, the current consumption in the active and standby modes is very different. (Image source: Texas Instruments)
In devices such as LDO, there may be a big difference between Iq and Id. For example, Iq of LDO is 25 nA and Id is 3 nA. In another case, Iq of LDO is 0.6 μ A. Id is 0.01 μ A。 Of course, it‘s not that simple:
·The operating temperature affects Iq and Id. This may be an important consideration for devices that are used at higher temperatures for a long time.
·The response time of low Iq devices to dynamic load changes may be longer. This factor varies greatly between different LDOs.
·Low Iq devices may generate internal noise, which may be an important consideration in noise sensitive applications.
·Even LDOs can get very hot, so the guidelines in the data book must be followed in terms of layout and thermal management. Otherwise, the performance of Iq and Id may be affected.
·The lowest IQ is not necessarily the best choice. If the difference between Iq and conduction current consumption is greater than two orders of magnitude, LDO with lower cost and higher Iq may be a good choice.
150 mA Low Iq LDO and Demo Board
When designing a system using a single lithium ion battery, if you need an LDO with a rated input voltage of 1.4 V to 6.0 V and an output current up to 150 mA, you can consider LDO devices such as MCP1711 provided by Microchip Technology. Typical Iq of the device is 0.6 μ A. Id is 0.01 μ A。 When the off mode is enabled, the output capacitor discharges through the special switch in MCP1711 to quickly reduce the output voltage to zero. The ambient operating temperature range of MCP1711 is - 40 ℃ to+85 ℃.
In order to explore the operation of MCP1711 in a wide range of input voltage and load, designers can use ADM00,672 demonstration board, which includes two voltages and two packaging options.
·1.8 Vout, input range 3.2 V to 6.0 V, five lead SOT-23 package
·3.3 Vout, the input range is 4.0 V to 6.0 V, and the four lead 1x1 UQFN package is adopted.
The demonstration board contains two isolation circuits that can be independently tested (Figure 2).
Figure 2: MCP1711 demonstration board includes two independent circuits, which provide 1.8 V (top) and 3.3 V (bottom) respectively. (Image source: Microchip Technology)
Fast transient response and low Iq
If fast transient response and low Iq are beneficial to the system, the designer can use Texas Instruments TPS7A02. The rated current of the device is 200 mA, Iq is 25 nA, and Id is 3 nA. The device supports 0.8 V to 5.0 V output voltage and can be set in 50 mV steps. The typical transient response of this LDO is less than 10 μ S Establish time with 100 mV down rush for step load changes from 1 mA to 50 mA. As shown in Figure 3, its response characteristics are different when the load increases and decreases. The specified junction temperature of TPS7A02 is - 40 ° C to+125 ° C.
Figure 3: The dynamic load response characteristics of TPS7A02 are different when the load increases (left) and decreases (right). (Image source: Texas Instruments)
epilogue
Iq is an important parameter to be considered when designing long battery life, but it is only one of several factors to be considered. According to the working condition and power consumption mode of the device, Id is also an important consideration. There are many factors, such as operating temperature, that affect Iq and Id, and these two values have an optimal range. Small is not always a good thing.
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