WO2013060802A1

WO2013060802A1 - Battery-operated electronic device and method

Info

Publication number: WO2013060802A1
Application number: PCT/EP2012/071190
Authority: WO
Inventors: Erkki Nokkonen; Peter Thomsen
Original assignee: St-Ericsson Sa
Priority date: 2011-10-25
Filing date: 2012-10-25
Publication date: 2013-05-02

Abstract

In a battery-operated device, the current and/or voltage of the battery is continuously monitored and measured. Conditions that will (if unmanaged) result in exceeding battery capability are detected in real-time, and the main peak power consumers (typically CPU, graphics and power amplifiers) are instantly limited ("Throttled") to decrease their power consumption momentarily.

Description

BATTERY-OPERATED ELECTRONIC DEVICE AND METHOD

[0001] The present invention relates generally to battery-operated electronic devices, and in particular to a system and method of managing battery power by adaptively throttling system operations in response to power consumption demands placed on the battery.

BACKGROUND

[0002] Battery-operated devices, such as Smart Phones and Tablets, may contain numerous functions, such as cellular modem & RF system; digital camera with flash; audio amplifiers (for integrated hands free speakers); high-bandwidth dynamic memory; and powerful processors, such as CPU(s) and graphics engines.

[0003] These functions all consume high peak currents from the battery during their operation. The cellular RF transmitter's power level is dictated by the cellular network. The highest peak current can occur during a GSM call, and can be in the order of 1.5-2 Amps, while the peak's duration is -0.57 ms, repeating at 217 Hz rate. Camera flash - especially LED flash - can consume currents up to 2 Amps for -100 ms. Audio amplifiers can consume 1-2 Amps or even more when equipped with a boosted supply (converting battery voltage up to, e.g., 6V level), depending on the volume setting and the music/speech that is being played.

[0004] The device's battery (typically Li-ion) has an impedance on the order of 100-150 mOhm, and thus current drawn from the battery causes a voltage drop (IR drop) at the battery's output. Furthermore, there is some impedance on the device's printed wiring board, causing further voltage drop. Each consumed ampere will cause, e.g., 150 mV drop, which is significant especially in the case of a single cell Li-ion battery (nominal voltage at 3.7 V).

[0005] The battery voltage is typically monitored using an analog to digital converter (ADC). In addition, one or more comparators may monitor the cut-off level, also known as the under voltage lock out, or battery good level. Software decides to switch off the device when the measured battery voltage falls below a predetermined threshold, e.g., 3.1 V. The comparator's threshold is set lower (e.g., 2.9 V) and it may switch off the device without software intervention if battery voltage falls below this level. The cut-off level is chosen so that all functions of the device are functional when battery voltage is higher than this level.

[0006] The battery voltage rail is capable of handling one peak current consumer at a time (i.e., the voltage drops are manageable in this situation). Problems start to occur when two or more peak current occur simultaneously. The sum of currents cause a big voltage drop on the battery voltage rail which can cause an unwanted switch-off of the device, without a pre-warning for the user. Another consequence is that the device switches off while there is still a lot of charge left in the battery, thus resulting in poor operating time.

[0007] The events that trigger the peak currents are independent, and thus difficult to control.

[0008] The TPS 6130x family of LED camera flash drivers, available from Texas

Instruments^®, are an example of prior art attempts to manage battery power consumption. A TPS6130x device controls an LED flash partially in response to a signal from a cellular modem. The signal is activated when the cellular RF is transmitting (or when the RF power level exceeds a certain threshold) and causes the flash driver IC to lower the power (current) delivered to the LED momentarily.

[0009] This prior art approach only addresses one specific case - an LED flash in the face of a cellular modem transmitting. Furthermore, it assumes a very predictive behavior that does not describe a general battery-operated device in which over-current consumption can occur due to unpredictable events, such as a 3^rd party application triggering high CPU and graphics load while coinciding with other events such as WLAN and/or cellular transmission.

[0010] Many battery-operated devices, such as mobile phones, may include a current gauge (or Coulomb counter) for monitoring the battery's state of charge. The gauge uses typically a 10 mOhm sense resistor located in the ground terminal of the battery to measure the current. For battery monitoring purposes a relative slow measurement, possibly with averaging, is used (for example, one known solution uses typically a 250 ms "window"). Instantaneous battery current can not be measured with such a gauge.

[0011] Recent trends in battery-operated devices include the "giga hertz" race toward ever- faster processors, and use of multi-core CPUs. In the next few years, chips on the market may contain four cores, each running at 2-3 GHz. Additionally, a device may include processors dedicated to processing graphics, video, images, cryptography, (de)compression, and the like. The performance, and hence (instantaneous) power consumption of these processors is also increasing. All this will result in very high peak power needs - yet another peak consumer with similar current levels as discussed above, or even higher. It should be noted that the power consumption of the processor is not only dependent on the clock frequency, but also the operations being performed (program code or data), and is thus highly unpredictable.

[0012] The classic engineering approach to dimension a system is to ensure that the worse case situation is within the normal system capability. In the case of battery-operated devices, this would mean that processors and other main power consumers would be limited in maximum performance, so that the sum of worst-case peaks does not exceed the battery capability. The problem with this approach is that performance is limited unnecessarily, as generically the events (or coincidence of events) that actually cause over-current are rare. Hence systematic approaches will unnecessarily deteriorate the user experience.

[0013] Another theoretical approach is to predict the simultaneous operation of processors, transceivers, and other high-power consumption subsystems, and coordinate their operations in software to avoid the sum power requirements exceeding the battery capacity. In practice, however, this approach is not feasible, since on modern systems most of the application software is completely outside the control of the device designer. SUMMARY

[0014] According to embodiments of the present technology, the current and/or voltage of the battery is continuously monitored and measured. Conditions that will (if unmanaged) result in exceeding battery capability are detected in real-time, and the main peak power consumers (typically CPU, graphics and power amplifiers) are instantly limited ("Throttled") to decrease their power consumption momentarily.

[0015] One embodiment relates to a method of momentarily reducing the power consumption of a battery-operated device comprising a plurality of power-consuming subsystems. Battery power consumption is monitored, and a maximum allowed level of battery power consumption is detected. A peak battery power consumption detection signal is generated in response to detecting the maximum allowed level of battery power consumption. The power consumption of one or more subsystems is reduced in response to the peak battery power consumption detection signal. After a predetermined duration, the power consumption level of the subsystems for which power consumption was reduced is restored.

[0016] Another embodiment relates to a battery-operated device. The device includes a battery and a power management unit connected to the battery. The power management unit is operative to monitor battery power consumption; detect a maximum allowed level of battery power consumption; and generate a peak battery power consumption detection signal in response to detecting the maximum allowed level of battery power consumption. The device also includes one or more battery-powered subsystems receiving the peak battery power consumption detection signal. At least one battery-powered subsystem is operative to reduce its power consumption in response to the peak battery power consumption detection signal; and restore its power consumption level after a predetermined duration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a functional block diagram of a battery-operated device having a current- based battery power consumption monitoring circuit.

[0018] Figure 2 is a functional block diagram of a battery-operated device having a voltage- based battery power consumption monitoring circuit.

[0019] Figure 3 are timing diagrams depicting a dynamic method of battery power control based on current sensing.

[0020] Figure 4 are timing diagrams depicting a dynamic method of battery power control based on voltage sensing.

[0021] Figure 5 is a flow diagram illustrating steps in a method of momentarily reducing the power consumption of a battery-operated device.

DETAILED DESCRIPTION

[0022] The present technology comprises two alternative embodiments of detecting when a total system current is about to exceed the battery capability: using a sense resistor of the current gauge to measure instantaneous current, and measuring directly the instantaneous voltage on a battery.

[0023] The embodiments are described with reference to Figures 1 and 2.

[0024] In one embodiment, depicted in Fig. 1 a battery-operated device 10, such as Smart Phones and Tablets, may contain numerous functions, such as cellular modem 20 & RF system 30; digital camera with driver 40 and flash 50; audio amplifiers 60 (for integrated hands free speakers 70); high-bandwidth dynamic memory; and powerful processors 80, 80', such as CPU(s) and graphics engines. Further, the battery operated device 10 includes a battery 100 and a PMU (power management unit) 101 connected to the battery 100. A sense resistor 102 is connected to both the current gauge 103 and a sense amplifier 104, which in turn connects to a set of comparators 105, each having a predefined threshold (reference voltage). [0025] In another embodiment of a battery-operated device 10', depicted in Fig. 2, the battery voltage is monitored using a fast comparator 105'. The voltage is compared to a predefined level which set above the system cut voltage (absolute minimum operating voltage).

[0026] The comparator(s) 105, 105' for the two embodiments are followed by digital logic circuitry 106 which provides selection of the threshold (Vref), glitch filtering, etc.

[0027] Additionally, there are one or more signals towards the processors' clock

generator(s) 107, 107' (usually a PLL). The clock generator(s) 107, 107' and processor(s) 80, 80' can reside on another chip Soc (System on a Chip) 109. As used herein, the term

"processor" refers to any digital processing circuit, and includes, without limitation, a state machine, microprocessor, Digital Signal Processor (DSP), graphics processor, video processor, compression/decompression engine, cryptographic processor, image processor (e.g., camera controller), audio processor, or any combination thereof.

[0028] The predefined thresholds can be set by software (via a control bus 1 10), and can be changed as a function of the battery type, voltage, and temperature. When battery 100 is fully charged (voltage around 4 V) and temperature is normal, larger peak currents can be sustained. On the contrary, when battery 100 is low and/or cold, the threshold should be set lower.

[0029] When the battery current is detected to be higher than the selected threshold (first embodiment, or method 1 ) or when the battery voltage drops below the selected threshold (second embodiment, or method 2), the signal PeakDet 111 is asserted (see Figures 3 and 4, respectively). As a consequence, the clock generator (PLL) 107, 107' divides (e.g., halves) the processor clock frequency (glitch-less switching). The power (current) consumed by the processor 80, 80' is immediately reduced (halved), and thus the demand on the battery current is reduced, avoiding the excessive voltage drop over the battery 100.

[0030] When the clock has been reduced, the current will drop below the threshold again (method 1) and the voltage will rise above the voltage threshold (method 2), and the PeakDet signal 111 will be de-asserted. The PLL frequency is kept after the PeakDet signal de-assertion for a predefined time before returning to its original settings. This is done to avoid repeated throttling (oscillation) - see Figures 3 and 4.

[0031] The threshold setting requires margin to compensate for inaccuracies in detection (sense resistor and amplifier, comparators) and for compensating the detection latency - i.e., there is a delay before the detection and clock generation circuitry 107, 107' will react and thus the battery current will continue to increase meanwhile.

[0032] According to another embodiment, a method of momentarily reducing the power consumption of the battery-operated device 10 is illustrated by the flow diagram in Figure 5. The method comprises monitoring 200 battery power consumption; detecting 201 a maximum allowed level of battery power consumption; generating 202 a peak battery power consumption detection signal 111 in response to detecting the maximum allowed level of battery power consumption; reducing 203 the power consumption of one or more of the subsystems 20, 30, 40, 50, 60, 70, 80, 80', 109 in response to the peak battery power consumption detection signal; and restoring 204, after a predetermined duration, the power consumption level of the subsystems 20, 30, 40, 50, 60, 70, 80, 80', 109 for which power consumption was reduced.

[0033]

[0034] The above-described technology mentions only processor clock speed reduction, but the concept can be extended to provide control to other functions, such as reducing display- backlight momentarily, reducing max power transmission on the cellular RF system 30, reducing audio power amplifier 60 output, reducing memory interface speed (on DDR system), or any other large current consuming subsystem. The design of appropriate subsystem throttling circuits will be readily apparent to those of skill in the art, without undue experimentation, given the teachings of the present disclosure. In many cases, the required power consumption reduction may be achieved by reducing ("throttling") the operative current provided to a subsystem (e.g., the LED cameral flash 50 or LCD display backlight). [0035] Principles of the present technology are explained above in two embodiments for the purpose of complete and enabling disclosure to those of skill in the art. However, the present technology is not limited by the parameters or operation of these embodiments. For example, a plurality of thresholds associated with a plurality of signals (PeakDetl , PeakDet2, ... ) may be used to trigger various current-demand throttling actions in the system (as applied to both embodiments). Additionally, rather than the comparators in the first embodiment, a windowing flash analog-to-digital converter may be used. Furthermore, the two methods described herein may be combined (either can assert PeakDet), or may be used alternatively.

[0036] Embodiments of the present technology provide a way to introduce very high performance processors to battery-operated devices (especially phones and tablets equipped with a single-cell Li-ion battery).

[0037] According to embodiments of the present technology, the system can be

dimensioned so that it gives the maximum performance, but takes care that a battery rail 114 is not overloaded. If the battery capability is about to be exceeded by simultaneous peak consumption on several independent sub-systems, the processors' speed are momentarily reduced (e.g., halved) but return back to "normal" level as soon as the high-current demand situation is over.

[0038] According to embodiments of the present technology, the system automatically takes into account battery charging current. When charging is active, the current taken from the battery will be lower and thus higher peak loads can be allowed.

[0039] Unlike systematic maximum power reductions schemes (such as systematically reduce performance during cellular transmission, or limit performance when maximum backlight is used, etc.) embodiments of the present technology do not impact general performance, as the throttling is enabled only in actual event of excess power consumption.

[0040] Further, embodiments of the present technology are highly flexible as a

programmable threshold level is used to detect the high-current demand condition. The threshold can be adapted to match the exact capability of the battery 100 used on a given product, and may furthermore be adjusted for environmental factors such as temperature.

[0041] The present technology may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the technology. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

1. A method of momentarily reducing the power consumption of a battery-operated device (10) comprising a plurality of power-consuming subsystems (20, 30, 40, 50, 60, 70, 80, 80', 109), comprising:

monitoring (200) battery power consumption;

detecting (201 ) a maximum allowed level of battery power consumption;

generating (202) a peak battery power consumption detection signal (111 ) in response to detecting the maximum allowed level of battery power consumption;

reducing (203) the power consumption of one or more of the subsystems (20, 30, 40, 50,

60, 70, 80, 80', 109) in response to the peak battery power consumption detection signal; and

restoring (204), after a predetermined duration, the power consumption level of the

subsystems (20, 30, 40, 50, 60, 70, 80, 80', 109) for which power consumption was reduced.

2. The method of claim 1 wherein reducing the power consumption of one or more subsystems in response to the peak battery power consumption detection signal comprises reducing the frequency of a clock signal supplied to a processor.

3. The method of claim 1 wherein reducing (203) the power consumption of one or more subsystems (20, 30, 40, 50, 60, 70, 80, 80', 109) in response to the peak battery power consumption detection signal (111 ) comprises reducing the operative current supplied to a subsystem.

4. The method of claim 1 wherein detecting (201 ) a maximum allowed level of battery power consumption comprises comparing the battery power consumption to a predetermined threshold.

5. The method of claim 4 wherein the threshold is adjusted based on a specific battery ( 00) installed in the device.

6. The method of claim 4 further comprising sensing one or more environmental factors, and wherein the threshold is adjusted based on at least one sensed environmental factor.

7. The method of claim 4 wherein

monitoring (200) battery power consumption comprises monitoring battery current; and detecting (201 ) a maximum allowed level of battery power consumption comprises detecting a maximum allowed battery current; and

wherein the predetermined threshold comprises a predetermined battery current.

8. The method of claim 7 wherein detecting (201 ) a maximum allowed battery current comprises

averaging the battery current over a predetermined duration; and

detecting a maximum allowed average battery current over the duration; and wherein the predetermined threshold comprises a predetermined average battery current.

9. The method of claim 4 wherein

monitoring (200) battery power consumption comprises monitoring battery voltage; and detecting (201 ) a maximum allowed level of battery power consumption comprises detecting a maximum allowed battery voltage; and

wherein the predetermined threshold comprises a predetermined battery voltage.

10. The method of claim 9 wherein detecting (201 ) a maximum allowed battery voltage comprises comparing a battery voltage to the predetermined battery voltage using a comparator.

11. The method of claim 9 wherein detecting (201) a maximum allowed battery voltage comprises comparing a battery voltage to the predetermined battery voltage using a windowing flash analog-to-digital converter.

12. A battery-operated device (10,10'), comprising:

a battery (100);

a power management unit (101 ) connected to the battery (100) and operative to

monitor battery power consumption;

detect a maximum allowed level of battery power consumption; and generate a peak battery power consumption detection signal (1 11 ) in response to detecting the maximum allowed level of battery power consumption; and one or more battery-powered subsystems (20, 30, 40, 50, 60, 70, 80, 80', 109) receiving the peak battery power consumption detection signal (111 ) and operative to reduce its power consumption in response to the peak battery power

consumption detection signal (111 ); and

restore its power consumption level after a predetermined duration.

13. The device of claim 12 wherein the battery-powered subsystem (109) comprises a processor (80) and wherein the subsystem is operative to reduce the power consumption of the processor (80) in response to the peak battery power consumption detection signal (11 1 ) by reducing the frequency of a clock signal supplied to the processor. 4. The device of claim 12 wherein a battery-powered subsystem (109) is operative to reduce its power consumption in response to the peak battery power consumption detection signal (111 ) by reducing the operative current consumed by the subsystem.

15. The device of claim 12 wherein the power management unit (101 ) is operative to detect a maximum allowed level of battery power consumption by comparing the battery power consumption to a predetermined threshold.

16. The device of claim 15 wherein the threshold is adjusted based on the specific battery (100) installed in the device (10).

17. The device of claim 15 wherein the power management unit (101 ) is further operative to sense one or more environmental factors, and wherein the threshold is adjusted based on at least one sensed environmental factor.

18. The device of claim 15 wherein the power management unit (101 ) is operative to

monitor battery power consumption by monitoring battery current; and

detect a maximum allowed level of battery power consumption by detecting a maximum allowed battery current; and

wherein the predetermined threshold comprises a predetermined battery current.

19. The device of claim 18 wherein the power management unit (101 ) is operative to detect a maximum allowed battery current by

averaging the battery current over a predetermined duration; and

detecting a maximum allowed average battery current over the duration; and wherein the predetermined threshold comprises a predetermined average battery

current.

20. The device of claim 15 wherein the power management unit ( 01 ) is operative to

monitor battery power consumption by monitoring battery voltage; and

detect a maximum allowed level of battery power consumption by detecting a maximum allowed battery voltage; and

wherein the predetermined threshold comprises a predetermined battery voltage.

21. The device of claim 20 wherein the power management unit (101) comprises a comparator (105, 105') operative to compare the battery voltage to the predetermined battery voltage.

22. The device of claim 20 wherein the power management unit comprises a windowing flash analog-to-digital converter operative to compare the battery voltage to the predetermined battery voltage.