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How Long Will My Battery Last?
Understanding system design for maximum battery life
NXP Semiconductor

Overview
– Energy efficient “green” products and battery-powered devices are
becoming more common
– Consequently, designing for optimum battery life and power efficiency is
increasingly important.
– How is the life of your battery dependent on far more than just the active
power consumption of your components?
2

Agenda
– Active Power vs. Standby Power
– Understanding power specifications
– Understanding Duty Cycle
– Application Example
– The Arrow Oryx board
– Detailed Power analysis by component type
– MCU
– RF
– Interface
– Logic and discrete
Next Steps: recommendations for next generation Data Collection System
Data Collection System Block Diagram
– Summary
3

Active vs. Standby Power
– All devices specify maximum/typical
– Active power consumption (device fully functioning)
– Standby power consumption (device sleeping/standby and other modes)
– Real power usage (Duty Cycle) measured by ratio of time spent in each
of these modes
– Examples Duty Cycle (Active/Total) for common battery power
applications
– Data collection system:
– Transmitter Nodes: about 1%
– Receiver Node (host): Similar (usually line powered)
– Tablet computer: Varies depending on use
– 100% for video streaming
– Less than 50% for text input
– Note that different components used for different operations
4

Application Example
THE ORYX BOARD
5

Application Example
– System Controller: Arrow Oryx Board
6

ORYX Board Functional Block Diagram
7

ORYX Board Functional Elements
8

Power Supply
How much power is there to work with?
Power Source Options:
– External (e.g. Solar with LTC3105)
– From LPC11U14 USB Interface
– From LPCXpresso pinning interface
– From LPC-Link Debugger USB Interface
Rechargeable Lithium Battery
LIR2032 with 45mAh
Battery
Options
9

Key Components Power Consumption
Component Function Active Modes Low Power Modes
LPC11U14
ADXL345 on I²C Bus*
PCF8523 on I²C Bus*
Cortex-M0 Microcontroller
with USB and Smart Card
IF
3-Axis Accelerometer with
Dual IRQ for MCU wakeup
Real-Time Clock with IRQ
for MCU wakeup
Max. 12mA (50MHz)
Typ. 2mA (12MHz)
Avg. 130µA / MHz
Active Communication on I²C
Bus: 150 µA
Active Communication on I²C
Bus: 200µA
Deep Sleep: 360µA
Power Down: 2µA
Deep Power Down: 220nA
Standby Typ. 100nA
Time Keeping: 150nA
LM75B on I²C Bus* Temperature Sensor Active Measuring: 100µA Shutdown Mode: 200nA
PCF8885 on I²C Bus*
AT45DB041D on SPI Bus
LS013B4DN04 on SPI Bus
8 Channel Capacitive
Touch Sensor with MCU
wakeup
4 MBit serial Flash,
separate Power switch
96x96 memory LCD,
separate Power switch
Active 10µA
Read 13mA (50 MHz)
Page Program 22mA
Erase: 24mA
Sleep Mode: 100nA
Auto Standby: 20µA
Deep Power Down: 1.5 µA
1 Hz Update: 4µA Standby: 2µA
* There is an optional power control on the two I²C pull-up resistors. By disabling these, the power down current consumption of the I²C-pins of the LPC11U14 can be reduced .
10

Min/Max Power Consumption Range
LDO 3.0V
I²C
SPI
All Components Active: 14mA / 42 mW
MCU
Power Switch
Power Down Mode: 6.57µA / 21µW
2µA
Cap
LCD
Flash
– MCU in Power Down
RTC
Accl
2µA
– (Brown Out Detect disabled)
– LCD 0.5 Hz keep alive signal
– RTC Time-keeping 120nA
– Serial Flash OFF
– Capacitive Sense & Accelerometer in Sleep Mode
0.57µA
Note:
MCU Deep Power Down reduces
consumption to 220nA but will Tristate IO-
Pins (so nothing is done)
Duty Cycle = 100%
For Battery LIR2032 with 45mAh → 3.2 hours runtime (worst)
→ 285 days runtime (best)
11

Doing Something Useful:
Analog Data Acquisition
14 mA
1. Read ADC Data
20ms
2. Read I²C Bus Temperature
Sensor
6.57 µA
3. Update Display
1s
4. Go to Power Down Mode
Average Current
=
( µA×
20ms)
14000 + (6.57µA×
980ms)
1000ms
= 286.44µA
Duty Cycle = 20/1000= 2%
For Battery LIR2032 with 45mAh → 6.5 days runtime
12

Doing Something Useful:
Digital Clock
14 mA
1. Read Clock Data via I²C once
per minute
20ms
6,57 µA
2. Update Display
3. Go to Power Down Mode
60s
=
( µA×
20ms)
14000 + (6.57µA×
59980ms)
60000ms
Average Current = 11.23 µA
Duty Cycle = 20/60000= 0.03%
For Battery LIR2032 with 45mAh → 166 days runtime
13

Oryx Power Reduction Tips
– Maximum Display Update Speed is limited by SPI Interface
to 0.75Mbps
– Set MCU speed to match max SPI speed
– Any more performance is wasted
– Only update parts of display that change
– LCD draws most power when state of pixels change
– Less Lines to update = less time to finish and go back to
sleep
– Don‘t blank it and reload each time: just update
– Use external Brown Out detection
– MCU internal BOR consumes +50µA
14

Taking it to the Limits of Battery Life
MCU ANALYSIS
15

LPC11U14 Block Diagram
Up to 40 GPIOs
Power
Profiles
2 SSP
USB
Smart Card
Interface
16

LPC11U14 Feature List
– ARM Cortex-M0 core @ 50 MHz
– Memories:
– Up to 32 kB Flash, 6 kB SRAM
– Boot ROM
– Power Profiles
– Serial interfaces:
– USB, 2 SSP, I 2 C-bus interface with
Fast-mode Plus mode, USART with
Smart Card Interface
– Analog peripherals: 8-ch/10-bit ADC
– Temperature range: −40C to +85C
– Packages: 48-pin LQFP, 33-pin HVQFN,
48TFBGA (4.5x4.5mm)
– Other Peripherals:
– Up to 40 General Purpose I/O
– Four general purpose counter/timers
– Programmable Windowed Watchdog
Timer (WWDT)
– 12 MHz internal Oscillator
– Clock output function with divider
– Brown-Out Detect (BOD) with
4 thresholds
– Boundary Scan
– Unique device serial number for
identification
– Single 3.3V power supply (1.8V to 3.6V)
– Pin-to-pin compatible with LPC134x series
17

Power Profiles of LPC11U14
Embedded ROM code for optimized power control
CPU Performance
Flexible and easy switching
between power profiles
during runtime
~30% Increase in
Default
performance
~20-30% reduction
in active power
CPU Efficiency
Lowest Active Power
Runtime
18

What is CoreMark?
Processors and associated systems are getting increasingly complex requiring
increasingly complex benchmarks to analyze. The current and future EEMBC
benchmarks are aimed at specific embedded market segments and are very
successful at approximating real-world performance of embedded devices.
However, there is also a need for a widely-available, generic benchmark
specifically targeted at the processor core. Introducing CoreMark -- Developed by
EEMBC, this is a simple, yet sophisticated, benchmark that is designed specifically
to test the functionality of a processor core. Running CoreMark produces a
single-number score allowing users to make quick comparisons between
processors.
19

Coremark Scores
20

Current Measurements While Running
CoreMark Can Be Found in NXP Data Sheets
/* set_power mode options */
#define PWR_DEFAULT 0
#define PWR_CPU_PERFORMANCE 1
#define PWR_EFFICIENCY 2
#define PWR_LOW_CURRENT 3
21

Comparison of Data Sheet Current vs. CoreMark
Current for ATMEGA644PA
22

Comparison of Data Sheet Current vs. CoreMark
Current for PIC24FJ64
23

Comparison of Data Sheet Current vs. CoreMark
Current for MSP430FG4618
24

Comparison of Data Sheet Current vs. CoreMark
Current for LPC1114
25

Detailed Power Analysis by Component Type
26

Energy Efficiency
27

The Effect of Input Voltage on Energy
28

The Effect of Duty Cycle
29

But how long will my battery last?
The absolute battery life obviously depends on the application, but
we can compare the three microcontrollers when running a
repetitive CoreMark workload with a period of 10 seconds. All
microcontrollers running at 6 MHz powered by a 240-mAhr CR2032
coin cell battery.
The results are:
• LPC1114:
• MSP430:
• PIC24:
3.6 million iterations or 100 hrs of life
1.2 million iterations or 33 hrs of life
0.432 million iterations or 12 hrs of life
… your results may vary
30

Taking it to the Limits of Battery Life
LOW POWER RF
31

The Wireless Evolution
Power
NXP focus
market
Bluetooth
(short-range voice)
Wi-Fi
(internet)
IEEE802.11x
UWB
(usb2 cable replacement)
WSNs
(hundreds of applications)
IEEE802.15.1
IEEE802.15.4
250 kbps 1 Mbps 11-54 Mbps 200+ Mbps
Speed

RF Comparison Usage and Scenarios
Increasing priority
Implementation
Price
Power
Co-existance with
other networks
Large-scale
Networking stack
Small-scale
Networking stack
Wireless
Microcontroller
design route
Interoperability
Encryption
Datarate
Bluetooth Low High Poor No Yes No Yes Fair High
BT LE Low Low Poor No Yes No Yes Fair High
Proprietary Low Low No No No Yes No No Low
802.15.4 Low Low Good Yes Yes Yes Yes Good Low
WiFi High High Good Yes Yes No Yes Good High
– IEEE802.15.4 offers optimal solution
– Designed to operate in large networks of devices
– Lowest cost. Flexible design solution for many different applications
– No ‘application-profiles’ ensures design flexibility
– Lowest power with prospect of interoperability
– Co-existence with other wireless networks (e.g. Wi-Fi)

JN5148 Single Chip Wireless Microcontroller
– Microcontroller:
– High Performance 32-bit RISC CPU core – programmable clock, 4-32MHz
– 8mm x 8mm sawn QFN 56 leads
– Operating voltage 2.0V to 3.6V
– Rich User Peripherals – mixed digital and analogue
– UARTs, SPI, 2-Wire Serial (I²C), GPIO, Timers, 3 x PWM, 12-bit ADC, DAC, Comparators
– JTAG debug port,
Watchdog timer
RAM
128kB
ROM
128kB
SPI
– Large memory footprint - 128kBytes RAM
– 128kBytes ROM for 15.4 MAC, stacks
– IEEE802.15.4 2.4GHz transceiver
– Time of Flight ranging engine
– 98dB link budget, achieving 30-50m indoors
2.4GHz
Radio
Power
Management
Ranging Engine
O-QPSK
Modem
IEEE802.15.4
MAC
Accelerator
128-bit AES
Encryption
Accelerator
RISC CPU
32-byte
OTP eFuse
2-wire serial
Timers
UARTs
4-Wire Audio
Sleep Counters
12-bit ADC,
comparators
11-bit DACs,
temp sensor
– 128-bit AES encryption, highly secure networking
– System implementation
– Low sleep power consumption - 1.3µA with timer
– Low power - 15mA TX, 18mA RX (35% less than competition)
– External BOM (

Analog Peripherals
• A/D Converter
» 12 bit SAR for excellent precision
» Four (4) open channels
» Internal temperature
» Internal supply voltage
» Single or continuous conversion
» Conversion time 40μsecs
» Offset voltage Section 22.3.8 of
the datasheet
• Comparator (two)
» Rail-to-rail inputs
» Programmable hysteresis
• DAC (two)
» 12 bit
» Min conversion time of 10μsecs
(2MHz clock)

ADC Versus Comparator
• A/D Converter
» Need to wake up and take a
reading
» Consumes 655µA for every
12-bit ADC reading
» Also, power consumed to
wake up processor
• Comparator
» Always on, even if asleep
» Consumes only 0.8µA
» Instant interrupt trigger
» Use for voltage, temperature,
etc.

Power Up Curve
– Key design requirement for most Low Power RF applications
– TX current = 15.0mA
– RX current = 17.5mA
– Green Energy Specification
– Meets requirements for 3 pulses from

Power Management
Feature
In Active Processing
mode: User can trade off
processing power against
current consumption
CPU Speed Power Consumption
4 MHz 2.75mA
8 MHz 3.85mA
16 MHz 6.1mA
32 MHz 10.6mA
Sleep power consumption
Additive Base
Chip
Module
Sleep with I/O wake-up 0.12µA 1.3µA
Sleep with I/O and 32kHz RC timer wakeup 1.3µA 2.6µA
Retain all 128KB of RAM in sleep
+ 2.2µA
Comparator in sleep
+ 1.2µA
32kHz crystal oscillator as an alternative to 32kHz RC
+ 0.4µA
Deep sleep mode wake on reset or I/O event
90nA

Battery Life when Pinging Data Such as RFID
Number of Years
– Battery life depends upon how often Tags transmit data:
12
10
8
6
4
2
0
Battery Life (Years)
0 10000 20000 30000 40000 50000 60000 70000
Ping Interval (mS)
Ping Interval
(ms)
1000
(once a second)
5000
(once every 5
Battery Life (yrs)
seconds)
30000
(once every 30
seconds)
60000
(once a minute)
*Assuming Tag is powered by a 560mAh coin cell (CR2477)
Approximate
Battery
Life*
193 days
2.4 years
7.5 years
9.8 years

Communication Modes
Remote
Node
2
7
8
1
Message
MAC Ack
App Ack
MAC Ack
Router
– MAC acknowledge and application acknowledge
– Assures that command was received
– Remote node has to stay in receive mode for a very long time
– Half of bandwidth is used for application acknowledge
– Used when remote node needs absolute confirmation that message
was received and processed
– Large power consumption
6
3
5
4
Message
MAC Ack
App Ack
MAC Ack
Destination
Node

Communication Modes
Remote
Node
1 3
Message
– MAC acknowledge only
Router
2 4
MAC Ack
Message
MAC Ack
Destination
Node
– Remote node powers off as soon as MAC ack is received
– Much lower power consumption
Remote
Node
1
Message
• No Acknowledge
Router
• Remote node powers off immediately after sending
• Remote node has no idea if data was received
• RFID type of applications
2
3
Message
MAC Ack
Destination
Node

Maximizing Battery Life
– NXP LPRF devices have on board regulator
– Apply voltage between 3.3V and 2.0V
– Coin cells or alkaline can meet this requirement
– No Super Cap required
– Even works if external serial flash for code storage
– Internal ADC measures battery voltage
– Do not waste user ADC channels
– Can send battery measurement to destination node
Alkaline
or coin
cell
+
Regulator
Super
cap
JN5168
Serial flash

Taking it to the Limits of Battery Life
INTERFACE ANALYSIS
43

Capacitive Proximity Sensor Family
Switching and detecting as from ghost hands
Value proposition of NXPs Cap Sensors:
• Lowest power Sensor in the market (typ. 3µA … 10µA)
• Extended battery voltage operating range (VDD = 2.5V to 9V)
• Auto (self) calibration disregards contamination
• Adjustable sensitivity and response time for each channel
separate
Part PCF8883T/1 PCF8885T/1 /2 ; PCA8885T/Q900/1 PCA8886T/Q900/1
Key
Features
• Single channel
• 3uA (typ.)
• Touch and proximity
• Does not require a microcontroller
• 8 channel
• 10µA (typ); Sleep Mode:

F
PC 8885 8-Channel Capacitive Proximity Sensor
A
Block Diagram
CPC 8
Sensor logic
Function description
For each sensor location a pair of “contact plates” are needed.
Matrix with 28 sensors can be controlled with a single device, 80 with 2
devices
When a key is touched 2 things happen:
the key# pressed is written to the sense register
generate an interrupt
The interrupt will alert the microcontroller and the switch code can be
read out. With accessing the I²C-bus the interrupt is cleared and the
circuit is ready for the next touch.
CPC 2
VSS VDD SCL SDA SA0 INT
OSC
Supply
Interrupt
Sense register 1
Sense register 2
I 2 C-bus interface
Contact plates
Key Features
• Based on the EDISEN patented algorithm
• I 2 C-bus interface
• One sub address to enable up to 80 keys with two devices
• Sleep mode, activated via I 2 C-bus or external input
• Three sensing modes: one key, two keys and N-keys
• Two event handling modes: direct mode and latching mode
• Adjustable scan frequency
• Channel masking feature
• Fast start up mode
• AEC-Q100 compliant automotive qualification (PCA8885)
45

NXP Real-Time Clock Families
Low-Power RTC Family (PCF85063, PCF2123, PCF8523):
Main Features / Value Proposition:
‣ Industry lowest power consumption (

NXP Ultra Low Power RTCs
Key Features:
• Accurate time based on 32kHz quartz
oscillator, electrical tuned
• Time from seconds ... Years
• Timer, Counter, Watchdog,
• Low power: 100nA operating current
• SPI-bus (PCF2123), I 2 C-bus (PCF8523)
Applications:
Card readers
Metering (gas, water, electric)
Handheld, battery operated
Medical, home blood-pressure, diabetes
Smart cards with one-time-password
Cut system power, by just running the
RTC to wake-up the controller periodically
47

NXP Small Footprint Low Power RTCs
Available Versions:
– PCF85063TP: I 2 C-bus, Limited feature set, 8-pin package
– PCF85063ATL: I 2 C-bus, Full feature set, 8-pin package
– PCF85063BTL: SPI-bus, Full feature set + CLKOUT, 10-pin package
Features
– Low power consumption: at
V DD =2.0V,T AMB =25°C, no bus activity, and
CLKOUT active, I DD =260 nA (typ.)
– Very small footprint packages
o HXSON8, 2.1mm x 3.1mm x 0.5mm;
0.5-mm pitch
o HXSON10, 2.7mm x 2.7mm x 0.5mm;
0.5-mm pitch
– Two interfaces supported; I 2 C and SPI
– Two integrated programmable oscillator
capacitors
o For 7 pF load and 12 pF load
Target Applications
– Printers
– Copy Machines
– Digital Still Cameras
– Digital Video Cameras
Function PCF85063TP PCF85063ATL PCF85063BTL
Electronic tuning Yes Yes Yes
I 2 C-bus
SPI interface
Sampling
P
1 min interrupt No Yes Yes
Alarm facility
Timer
CLK out
CLK enable
Interrupt output
Package
SOT number
No
No
Yes
No
Yes
HXSON-8 †
SOT1052
† 0.5-mm pitch
P
Yes
Yes
Yes
No
Yes
HXSON-8 †
SOT1052
P
Yes
Yes
Yes
Yes
Yes
HXSON-10 †
SOT1197
48

Taking it to the Limits of Battery Life
LOGIC ANALYSIS
49

The Power of Logic
– 12 primary logic families (ranked by standby current)
Logic
Family
Operating
Voltage
Standby
Current
µA
Max Drive
mA
AUP 0.8-3.6 0.9 4
LV 1.0-3.6 20 8
LVC 1.2-3.6 20 24
AVC 1.2-3.3 20 8
AHC 2.0-6.0 40 8
ALVC 1.2-3.6 40 24
HC 2.0-6.0 80 8
ALVT 2.3-3.6 90 64
FAST 4.5-5.5 90 24
LVT 2.7-3.6 120-190 64
ABT 4.5-5.5 250 64
HEF4000 5.0-15.0 600 3
50

Load Switches
The ultimate power saving device
Select the Active Devices based on specific application running. If the
device is not needed, turn off its power!
Low cost, distributed Load Switches allow highly granular control of
power to every device in the system
Ex: NX3P190
– 1.1-3.6V supply voltage
– 95mohms ON resistance
– Maximum switch current: 500mA
– Low ground current = 2 µA (Active)
– Power off leakage current = 2 µA (Standby)
– Note: if a device already has a standby mode LESS than 2 µA
consider grouping several together on one load switch
51

Load Switches
More than just a FET
Operating Voltage: up to 6.5V
Drive Current: up to 3A
Reverse Voltage
Comparator
IN
Current
Sense
OUT
Charge
Pump
EN
Driver
Logic
Current
Limiter
UVLO
R
discharge
Thermal
Sense
Fault
Logic
FAULT
ILIMIT
52

Load Switches
Feature Examples
Product Overview
Part
Input
voltage
(V)
Ron @1.8 V
(mW)
Feature
Max Current
(A)
Enable Pin
Package
(mm)
Target
Applications
NX3P190UK 1.1 to 3.6 95 Slew rate 0.5 Active high
WSCP4
0.8X0.8,0.4p
Mobile,
computing
NX3P191UK
1.1 to 3.6 95
SR, Load
discharge
0.5 Active high
WSCP4
0.8X0.8,0.4p
Mobile,
computing
NX5P198UK 2.0 to 5.5 28
SR, Reverse
polarity
3.0 Active high
WCSP6
1.0X1.5,0.5p
Mobile,
computing
NX5P1039 1.8 to 5.5 20 Slew Rate 3.0 Active high
WCSP6
0.8x1.2,0.4p
1.0X1.5, 0.5p
Mobile,
computing
NX3P2553 2.5 to 6.5 85
Constant
current limit,
UVLO, temp
SD
3.0
Active high
QFN:6 2.0x2.0
PG: 3.0x3.0
TV / LCD,
computing
53

Improving Oryx
Going for ultimate power savings
Load
Switch
* Load
Switch
Load
Switch
Load
Switch
Load
Switch
•Note: since Load Switch requires external enable control one
device such as RTC interrupt or MCU (in standby mode) will not be
controlled by Load Switch
•Group several low power devices together on single Load Switch
54

Example: “rotating globe” (with Load Switch)
– Devices needed
– Devices not needed
Device
Power
Saved (uA)
LPC-Link 2
X
O
X
Accelerometer 0.1
Temp Sensor 0.2
RTC 0.15
FLASH 1.5
X
O X
Load Switch - 2
Total 1.95
X
O
Extra life expected from Battery → x.x hours Little savings due to CPU intensive app
55

Example: Real Time Clock (with Load Switch)
– Devices needed
– Devices not needed
•Only the RTC has power:
all other devices disabled
via single load switch
•RTC interrupt connects to
load switch EN
•At power up, MCU updates
display then powers down
X X
X O
Extra life expected from Battery → x.x days runtime
X
O
X
56

Taking it to the Limits of Battery Life
ANALYSIS OF OTHER DEVICES
57

Non-NXP Device Analysis (1)
• LTC4071: Shunt Charger with
Low Battery Disconnect
• Standby Current (

Non-NXP Device Analysis (2)
– Ultra Low Power Consumption
– 1.35’’ Type LS013B4DN01: 6µW static content / 12 µW up-date at 1 Hz
– < 1% compared to backlit TFT LCD of same size
– app. 10% compared to HR TFT LCD of same size
– suitable for energy self-sustaining applications
– Excellent readability
– Very thin: 0.55 - 1.53 mm depending on model
Basic Working Principle
Power Supply OFF
LC is in scattered state
Pixel color is white, same as scattered light
Power Supply ON
LC is in transparent state
Pixel color same as reflective backplate
59

For Future Thought:
Application Example
– Data Collection System
1 2 3 4
Temp sensor
Solar Cell
Oryx
Oryx
Oryx
Oryx
Interface
Temp sensor Solar Cell board
Light sensor
Interface
board
Temp sensor Solar Cell
Light sensor
Zigbee RF (Transmit)
Interface
Motion sensor
board
Temp sensor Solar Cell
Light sensor
Zigbee RF (Transmit)
Motion sensor
Interface
Remote board Unit (x4)
Light sensor
Zigbee RF (Transmit)
Motion sensor
Zigbee RF
(Receiver)
Oryx
Motion sensor
Zigbee RF (Transmit)
4 identical nodes
60

Conclusion
– The device specification is only the starting point for ultra-lowpower
design
– Duty cycle is often more critical than max power consumption
– System may run multiple applications each with unique power
curves and duty cycles
– Start optimization with the largest power users and work towards
the point of diminishing returns
– “Power off” is the ultimate low power state: look for those
opportunities
61