PIC Microcontroller Low Power Tips ‘n Tricks CHAPTER 2 PIC ...

1 PIC Microcontroller Low Power tips n Tricks CHAPTER 2. PIC Microcontroller Low Power tips n Tricks Table Of Contents tips N Tricks INTRODUCTION. Microchip continues to provide innovative products that are smaller, faster, easier to GENERAL LOW Power tips N Tricks . use and more reliable. The Flash-based PIC . TIP #1 Switching Off External Circuits/ microcontrollers (MCUs) are used in an wide Duty 2-2. range of everyday products, from smoke TIP #2 Power 2-3 detectors, hospital ID tags and pet containment TIP #3 Configuring Port 2-4 systems, to industrial, automotive and medical TIP #4 Use High-Value Pull-Up 2-4 products. TIP #5 Reduce Operating 2-4. TIP #6 Use an External Source for PIC MCUs featuring nanoWatt technology CPU Core 2-5 implement a variety of important features which TIP #7 Battery Backup for PIC MCUs.

2 2-6 have become standard in PIC microcontrollers . Since the release of nanoWatt technology, DYNAMIC OPERATION tips N Tricks changes in MCU process technology and TIP #8 Enhanced PIC16 Mid-Range 2-6 improvements in performance have resulted in TIP #9 Two-Speed 2-7 new requirements for lower Power . PIC MCUs TIP #10 Clock 2-7 with nanoWatt eXtreme Low Power (nanoWatt TIP #11 Use Internal RC 2-7 XLP ) improve upon the original nanoWatt TIP #12 Internal Oscillator 2-8 technology by dramatically reducing static TIP #13 Idle and Doze 2-8 Power consumption and providing new flexibility TIP #14 Use NOP and Idle 2-9 for dynamic Power management. TIP #15 Peripheral Module Disable The following series of tips n' Tricks can be (PMD) 2-9.

3 Applied to many applications to make the most STATIC Power REDUCTION tips N Tricks of PIC MCU nanoWatt and nanoWatt XLP. TIP #16 Deep Sleep 2-10 devices. TIP #17 Extended WDT and Deep Sleep 2-10 GENERAL LOW Power tips N. TIP #18 Low Power Timer1 Oscillator Tricks . and 2-10. TIP #19 Low Power Timer1 Oscillator 2-11 The following tips can be used with all PIC. TIP #20 Use LVD to Detect Low 2-11 MCUs to reduce the Power consumption of TIP #21 Use Peripheral FIFO and 2-11 almost any application. TIP #22 Ultra Low- Power Wake-Up 2-12. 2009 Microchip Technology Inc. DS01146B-Page 2-1. PIC Microcontroller Low Power tips n Tricks TIP #1 Switching Off External Example: Circuits/Duty Cycle The application is a long duration data recorder.

4 All the low Power modes in the world won't help It has a sensor, an EEPROM, a battery and a your application if you are unable to control microprocessor. Every two seconds, it must the Power used by circuits external to the take a sensor reading, scale the sensor data, microprocessor. Lighting an LED is equivalent store the scaled data in EEPROM and wait for to running most PIC MCUs at 5V-20 MHz. the next sensor reading. When you are designing your circuitry, decide what physical modes or states are required and partition the electronics to shutdown unneeded circuitry. Figure: 1-1. C2. F. U1. VDD. 100k R2. R4. 10k 10k R5. MCLR. RA0 RB0/INT. U2. R3. RA1 RB1 VCC A0.

5 1k RA2 RB2 WP A1. F. C1. RA3 RB3 SCL A2. RA4/TOCKI RB4 SDA GND. RB5. Serial EEPROM. OSC1/CLKIN RB6 Y1. 22 pF. R1 OSC2/CLKOUT RB7. C3. 100k VSS kHz 33 pF. 33 pF. C5. C4. PIC16F819. The system shown above is very simple In Figure 1-2, I/O pins are used to Power the and clearly has all the parts identified in the EEPROM and the sensor. Many PIC MCU. requirements. Unfortunately, it has a few devices can source up to 20 mA of current problems in that the EEPROM, the sensor, and from each I/O, so there is no need to provide its bias circuit, are energized all the time. To additional components to switch the Power . get the minimum current draw for this design, If more current than can be sourced by the PIC.

6 It would be advantageous to shutdown these MCU is required, the PIC MCU can instead circuits when they are not required. enable and disable a MOSFET to Power Figure: 1-2 the circuit. Refer to the data sheet for drive capabilities for a specific device. C2. F. U1. VDD. 100k R5. R4. 10k R2. 10k MCLR. RA0 RB0/INT. U2. R3. RA1 RB1 VCC A0. 1k RA2 RB2 WP A1. F. C1. RA3 RB3 SCL A2. RA4/TOCKI RB4 SDA GND. RB5. Serial EEPROM. OSC1/CLKIN RB6 Y1. 22 pF. R1 OSC2/CLKOUT RB7. C3. 100k VSS kHz 33 pF. 33 pF. C5. C4. PIC16F819. Page 2-2-DS01146B 2009 Microchip Technology Inc. PIC Microcontroller Low Power tips n Tricks TIP #2 Power Budgeting Computing Battery Life Power budgeting is a technique that is critical to Using the average current from the calculated predicting current consumption and battery life.

7 Power budget, it is possible to determine Power budgeting is performed by calculating how long a battery will be able to Power the the total charge for each mode of operation application. Table 2 shows lifetimes for typical of an application by multiplying that mode's battery types using the average Power from current consumption by the time in the mode Table 1. for a single application loop. The charge for Life each mode is added, then averaged over the Battery Capacity (mAh). total loop time to get average current. Table 1 Hours Days Months Years calculates a Power budget using the application CR1212 18 4180 174 .48. from Figure 2 in Tip #1 using a typical nanoWatt CR1620 75 17417 726 XLP device.

8 CR2032 220 51089 2129 Time Current (mA) Charge Alkaline AAA 1250 290276 12095 in Current *. Mode By Mode Alkaline AA 2890 671118 27963 Mode Time (mS) Device Total (mA * Sec) Li-ion* 850 197388 8224 Sleep NOTE: Calculations are based on average current draw only and MCU Sleep do not include battery self-discharge. Sensor Off 1989 0 EEPROM Off 0 *Varies by size; value used is typical. Initialize MCU Sleep After completing a Power budget, it is very easy Sensor On 1 to determine the battery size required to meet EEPROM Off 0 the application requirements. If too much Power Sample Sensor is consumed, it is simple to determine where MCU Run Sensor On 1 additional effort needs to be placed to reduce EEPROM Off 0 the Power consumption.

9 Scaling MCU Run Sensor Off 1 0 EEPROM Off 0. Storing MCU Run Sensor Off 8 0 +00 EEPROM On 1. Total 2000 Average Current = mA*Sec 2000e-3 Sec = mA. Peak Current mA. 2009 Microchip Technology Inc. DS01146B-Page 2-3. PIC Microcontroller Low Power tips n Tricks TIP #3 Configuring Port Pins TIP #4 Use High-Value Pull-Up All PIC MCUs have bidirectional I/O pins. Some Resistors of these pins have analog input capabilities. It It is more Power efficient to use larger pull-up is very important to pay attention to the signals resistors on I/O pins such as MCLR, I2C . applied to these pins so the least amount of signals, switches and for resistor dividers. For Power will be consumed.

10 Example, a typical I2C pull-up is However, Unused Port Pins when the I2C is transmitting and pulling a line low, this consumes nearly 700 uA of current for If a port pin is unused, it may be left each bus at By increasing the size of the unconnected but configured as an output pin I2C pull-ups to 10k, this current can be halved. driving to either state (high or low), or it may The tradeoff is a lower maximum I2C bus be configured as an input with an external speed, but this can be a worthwhile trade in for resistor (about 10 k ) pulling it to Vdd or Vss. many low Power applications. This technique is If configured as an input, only the pin input especially useful in cases where the pull-up can leakage current will be drawn through the be increased to a very high resistance such as pin (the same current would flow if the pin 100k or 1M.)