AN-1014 [CYMBET]

Using the AtmelÂ® picoPower AVR Microcontroller with Cymbet EnerChips; 使用AtmelÂ®的picoPower AVR微控制器与Cymbet的EnerChips


型号：	AN-1014
厂家：	CYMBET CORPORATION
描述：	Using the AtmelÂ® picoPower AVR Microcontroller with Cymbet EnerChips 使用AtmelÂ®的picoPower AVR微控制器与Cymbet的EnerChips 微控制器
文件：	总4页 (文件大小：829K)
中文：	中文翻译
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AN-1014

Application Note

Using the Atmel® picoPower™ AVR® Microcontroller

with Cymbet™ EnerChips™

A Demonstration Vehicle for Cymbet Solid State Thin Film Rechargeable Batteries

Consideration needs to be given to the minimum voltage needed

by the system to run off backup power, on how to switch between

main power and backup power, and on how to signal the

microcontroller that it will be running off backup power. Special

algorithms may be used so that the microcontroller sheds loads

and puts itself into a low-power sleep mode during backup.

The power-fail sensing circuit must not feed power back into the

main power bus when the system switches over to the EnerChip

for backup power. In the Demo Board, a 4.7 MOhm resistor is

used to limit current on the V_REFline to ≈500 nA. A diode would

have eliminated all current leakage and have been an even better

choice.

Figure 1. Cymbet Atmel picoPower AVR Demo Board.

Introduction

The Cymbet EnerChip and Atmel picoPower AVR are combined

in a demonstration board designed to show the advantages of

Cymbet EnerChip rechargeable batteries for embedded processor

applications. Cymbet EnerChips provide virtually unlimited

system life. They are smaller, lighter and environmentally

friendlier than primary lithium coin cells for backup power. The

demo board consists of an Atmel Atmega169P picoPower AVR

microcontroller with integrated LCD controller, Cymbet EnerChip

cells, and a Cymbet charge control circuit.

Figure 2. Charge Controller Block Diagram.

Charge Circuit Description

The charge circuit in Figure 4 meets all key system requirements.

It is powered by two lithium coin cells, so that no boost charge

pump is needed. Charge voltage regulation utilizes a Zetex

ZR40401F41TA shunt voltage regulator, but could also have

used a low I_QLDO, such as a TI TPS715XX regulator.

Current blocking to prevent the EnerChip from being discharged

when main power is off is implemented with transistors Q2, Q3,

and Q5. Transistors Q3 and Q5 are dual packaged devices, with

the two transistors wired in series so that the off-state leakage

current is negligible for a µAh-rated EnerChip.

System Considerations

Cymbet EnerChips are ideal for applications requiring a high

number of charge/discharge cycles, such as backing up

microcontrollers during intermittent power outages. Such systems

will need a charge controller to keep the EnerChip at a full state of

charge without overcharging the battery and thereby reducing its

useful life. The charge circuit will need a source of voltage higher

than the EnerChip charging voltage of 4.1V. This may require a

charge pump. The charge circuit must regulate the charge voltage

and have a means of isolating itself from the EnerChip (current

blocking) to prevent the EnerChip from discharging through the

charge circuit when system power is off. Isolation from the main

power supply and voltage reduction from the battery output to the

load may also be necessary.

PNP transistor Q2 is used as a comparator to shut off the charge

circuit when the input voltage falls below ≈ 4.8V (4.1V plus the

V_BEof the transistor). When Q2 turns off, N-channel FET Q3 is

turned off, which then turns off P-channel FET Q5.

DOC-111014 RevA

Page 1

AN-1014: Atmel picoPower AVR Demo Board

Demonstration Description

Software Description

Two on-board coin cells are used as the primary power source in The software uses an interrupt driven control loop. The processor

lieu of an external power supply. Place the two coin cells in series is normally in the “powersave” mode to conserve power. Timer2

in the coin cell holder, with the negative terminal toward the board is clocked off the external 32.768 KHz crystal and generates an

for both cells. Position the battery-select jumper to select the interrupt at 1 sec intervals. This wakes the processor, which will

correct EnerChip. Close power switch SW1 for charging. Also then update the display as needed, then go back to sleep.

press pushbutton S1 (at bottom left of board) to turn off the LCD

Timer Initialization Routine

display and minimize current drain. The EnerChip will be 80%

charged within 30 minutes and 100% charged after 45 minutes.

See AN-1003 for more details on battery charging times.

void timer2_init(void)

{

#asm("cli")

// clear global interrupt flag

After the battery is fully charged, slide the power switch to Off

and back to On. This will turn on the LCD display. The indicator

caption will be START. The board will wait for an operator input.

TIMSK2 = 0;

ASSR=0x08;

TCNT2=0x00;

TCCR2A = 0x05;

// disable OCIE2A and TOIE2

// use external 32 crystal

// clear counter

// divide by 8

while ((ASSR & 1) | (ASSR & 4));

// wait for tcn2ub and tcr2ub to clear

TIFR2 = 0x7F;

TIMSK2 = 0x01;

#asm("sei")

}

// set overflow limit

// set overflow interrupt enable bit

// reset global interrupt flag

LCD Setup Registers

Display ready for

timing.

Display while timing Display stopped

after pressing S2. after pressing S2.

LCDCRA=0x80;

LCDCRB=0xD7;

LCDCCR= 0x0F;

LCDFRR=0x02;

// normal waveform; buffers on

// now set for external clock 32.768

// contrast control

Press pushbutton S2 (at bottom right of board) to start the timer

function. The LCD will show elapsed minutes and seconds. The

indicator caption will be STOP. Press S2 again to stop timing. The

indicator caption will be CLEAR. Press S2 once more to clear the

display and reset the timer.

// clock divider

Other LCDs might require different settings. Further power

reductions can be obtained by turning off the buffers and using

the ATmega169 “Low Power” LCD waveform; however, this

may reduce the contrast and sharpness of the display. Consult

Atmel, www.atmel.com, for further details and latest information

on the ATmega169P AVR microcontroller.

Turn off power switch SW1 or remove the coin cells to demon-

strate Demo Board operation from the EnerChip alone.

Press pushbutton S1 (at bottom left of board) to toggle the LCD

display on and off. With the LCD off, current draw on the

EnerChip will be ≈ 2 µA. A 50 µAh CBC050 EnerChip will then

provide backup for 25 hours and a CBC012 EnerChip for 6 hours.

With the LCD on, current draw will be ≈ 14 µA, and the above

times will be reduced to 3.6 hours and 51 minutes, respectively.

To measure current draw, insert a micro-Ammeter in place of the

battery-select jumper.

The 3-1/2 digit LCD display will first show minutes and seconds

in MM:SS format. After 19:59 (19 min: 59 sec), it switches to

HH:MM format. After 19:59 (19 hrs: 59 min), the unit stops

counting.

When power switch SW1 is in the Off position, the display is

automatically blanked and the EnerChip is being discharged.

When finished with the evaluation, remove the battery select

jumper to prevent the EnerChip from becoming fully discharged,

possibly reducing its life.

DOC-111014 RevA

Page 2

AN-1014: Atmel picoPower AVR Demo Board

Figure 3. Schematic Diagram, Atmel ATmega169P Microcontroller.

DOC-111014 RevA

Page 3

AN-1014: Atmel picoPower AVR Demo Board

Figure 4. Charge Control Circuit.

Note: Atmel® and AVR® are registered trademarks of Atmel Corporation and picoPower™ is a trademark of Atmel Corporation. All other trademarks

are the property of their respective owners.

DOC-111014 RevA

Page 4

AN-1014 [CYMBET]

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