How to extend battery life with NCP171 from ON Semi
I was one of those people, who desperately wanted to buy Samsung Galaxy Note 7 when it first came out in 2016. However, due to a number of unfortunate events (several phones caught fire on the plane) followed by a flight ban by major airline companies, its production has been suspended. Samsung has claimed that overheating and explosions of Note 7 happened because of battery malfunction. Although exploding phones rarely make news headlines, there are more and more devices coming out every day that rely on one or another type of battery. Lithium-ion is the most well-known, but apparently you can make a battery from all the elements in the periodic table. However, our constant race for the smartest devices is causing yet another environmental crisis throughout the continents. From dead yaks floating down Tibetian rivers to a water shortage in South America, the minerals are being over-extracted to meet the demands of battery manufacturers. Cobalt, which is generally used in lithium-ion batteries, is not only dangerous and toxic, but it has also been placed as a “conflict material” due to the use of child labour for mining.
Along with the search for more sustainable and non-toxic materials to produce batteries, it is in our hands to try to extend battery life in our devices. On an individual level, shutting down the device when it is not on use (I am guilty of having my laptop on sleep mode for days occasionally). In broader terms, electronics manufacturing companies need to make it a priority to optimise the designs to ensure the prolonged shelf-life of batteries.
When it comes to battery-powered devices, one of the parameters that affect how long the battery can last is the quiescent current. This is specifically important for applications such as wearable devices or IoT, where the device is not used in full operation for most of the time (duty cycle is about 0.001 percent). Figure 1 shows the power profile for a typical battery-powered IoT node with Active Mode and Low Power Modes. During the Active Mode, the device could be performing sensing or transmitting, while in Low Power Mode corresponds to when the device is “sleeping” while being ready to wake up anytime.
Figure 1. Battery-powered devices in Active and Low Power Modes
Figure 2. Battery life versus duty cycle
So, what is quiescent current? Quiescent current, Iq is defined as a current drawn by the internal IC when there is no load and switching is not taking place. This means that there is no current flowing from the output pin, but the device is still on. If the device has control switches, they need to be closed. These two conditions imply that Iq is not coming from the input current that is transferred to the output or to the gate drivers. The Iq travels to the ground consuming the power provided by the connected battery or power source. The value of Iq solely depends on the IC and not the external components. In fact, Iq is used to power the IC to cover its basic functionalities such as an oscillator, internal precision voltage reference and thermal shutdown circuit.
NCP171 is a dual-mode LDO regulator from ON Semi with the output current up to 80mA in Active Mode and quiescent current in the range of tens of nA (50nA) in Low Power Mode. The device follows ON Semi’s previous Ultra-Low Power LDO regulator, NCP170 at 500nA IQ, resulting in the 10X improvement in the quiescent current from one generation to another. This significant reduction in IQ makes NCP171 ideal for battery-powered applications.
Some of the main features of NCP 171 include:
- Input voltage range: 1.7V to 5.5V
- Output voltage range: 0.6V to 3.3V
- Low dropout voltage: 41mV at 80mA (Vout = 3.3 V)
- Output voltage can be lowered by an internally programmed value of 50 mV, 100 mV, 150 mV, and 200 mV
- ±2% Output Voltage Accuracy in Active Mode
- High PSRR: 65 dB at 1 kHz in Active Mode
- Active Output Discharge for Fast Output Turn−Off
- Current Limitation, Thermal Shutdown
- Available in Small XDFN4 1.2x1.2 Package
Figure 3. The operation of NCP171
Figure 3 demonstrates the dual-mode operation of NCP171. The dynamic switching between Active and Low Power Modes is controlled through an ECO pin. The optimal operation based on the customer’s application can be selected by programming one of the microcontroller’s pins to output two-state logic and connecting that to the ECO pin. In Low Power Mode, the quiescent current is typically 50nA, which is more than 1000 times lower compared to Active Mode. In Active Mode, the value of the quiescent current is up to 100µA. The transition time from one mode to another is usually up to 100 µs.
Figure 4. Transitioning from Low Power Mode to Active Mode (left) and vice versa (right)
Let’s have a look at the load transient response of NCP171 (Figure 5), which is another parameter that describes the dynamic behaviour of the LDOs. This graph explains how the output voltage reacts to the sudden rise and drop in the load current value. Rise and drop time is usually in the order of a few milliseconds. The load current has changed from a few mA to maximum value for Low Power (5mA) and Active Power Mode (80mA). It can be noticed that both voltage waveforms experience fluctuations, but the undershoot is lower and voltage returns to the regulated value significantly faster in Active Mode.
Figure 5. Load transient response in Low Power (left) and Active Modes (right)
When it comes to battery-powered applications, switching regulators are generally preferred due to their higher efficiency. However, for cases when devices operate in Active and Low Power Modes, the battery could be extended for longer by using linear voltage regulators with low IQ. Table 1 below compares NCP170 and NCP171 to typical low IQ buck regulator. Here, we assume that in Low Power Mode the load current is in µA level.
Table 1. Calculating battery life for Low Iq LDO versus Buck regulator
ON Semi offers the STR-NCP171-EVK evaluation board to support designers in the prototyping stage (Figure 6). The board can be used in Strata environment GUI allowing to test out functionalities such as switching it between Active and Low Power Mode. Other parameters that can be monitored on Strata are input/output voltage, power dissipation, temperature, etc.
Figure 6. STR-NCP171-EVK evaluation board
Quiescent current of the regulator is one of the first parameters you have to look at if you have battery-powered applications in mind. The NCP171 LDO regulator could be ideal for this job since it draws a very low quiescent current (50nA) and has a very good dynamic performance. It even outperforms conventional buck regulators in terms of battery life in applications where the device consumes low power for an extended period of time. For more information on the NCP171 and evaluation board, you can refer to the attached datasheet.
The NCP171 evaluation board and LDO regulators will be available from soon, check back here for updates.