Linear Technology DC1812A Guida rapida alla configurazione

dc1812af

DEMO MANUAL DC1812A

Description

LTC2943

Multicell Battery Gas Gauge with Temperature,

Voltage and Current Measurement

Demonstration circuit 1812A(Figure 1) features the

LT C

2943. The LTC2943 has an operating range of 3.6V

to 20V making it perfectly suited for multicell battery ap-

plications. A precision analog coulomb counter integrates

current measured through a sense resistor between the

battery’s positive terminal and the load or charger. The

LTC2943 measures voltage, current and temperature with

aninternal14-bitNoLatency∆∑™ADC.Themeasurements

are stored in internal registers accessible via the onboard

SMBus/I2C interface.

The LTC2943 has programmable high and low thresholds

for all measured quantities. If a programmed threshold

is exceeded, the device reports an alert using either the

SMBus alert protocol or by setting a ﬂag in the internal

status register.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and No

Latency ∆∑ and QuikEval are trademarks of Linear Technology Corporation. All other trademarks

are the property of their respective owners.

The LTC2943 requires only a single low value sense resis-

tor to set the measured current range. The default value

assembled on the DC1812A is 100mΩ for a maximum

current measurement of 500mA. The LTC2943 has a

software-conﬁgurable charge complete/alert pin. When

the pin is set for charge complete, a jumper connects

the pushbutton which simulates a logic low input at the

AL/CC pin. This sets the ACR register to FFFFh which

indicates a full battery. When the pin is conﬁgured for

alert, the same jumper is used to connect a red LED that

indicates an alert is present.

The DC1812A is a part of the QuikEval™ system for quick

evaluation with a host controller through a PC using the

DC590.

Design files for this circuit board are available at

http://www.linear.com/demo/DC1812A

Figure 1. DC1812A

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DEMO MANUAL DC1812A

Quick start proceDure

Demonstration circuit 1812A is easy to set up to evalu-

ate the performance of the LTC2943. Refer to Figure 2

for proper measurement equipment setup and follow the

procedure below.

1. ConnectaLi-Ion battery across V_BAT andGND.Multiple

Li-ion batteries can also be used as long as the total

voltage does not exceed the operating voltage of the

device. The LTC2943 has a maximum operating voltage

of 20V, so for a 4.2V lithium ion battery the maximum

cell count would be 4 cells.

2. Connect a load across V_CHRG/LD and GND for battery

discharge measurement. Up to 500mA supplied from

the battery can be measured with the board default

100mΩ sense resistor. Use SENSE+and SENSE–test

points to read voltage across the sense resistor.

3. Connect a 2.7V to 5.5V battery charger supply across

V_CHRG/LD and GND for battery charge measurement.

Up to 500mA supplied to the battery can be measured

with the board default 100mΩ sense resistor. Use

SENSE+and SENSE–test points to read voltage across

the sense resistor.

4. Connect a DC590 to 14-pin connector J1 for evaluation

with QuikEval, or connect a host controller I2C bus to

the SDA, SCL and GND test turrets.

5. Ifahost I2Ccontrolleris used, then provide a bus pull-up

voltage to the +5V turret, else start QuikEval software

on PC.

6. Read and write to the LTC2943 through I2C.

7. Through I2C, configure the AL/CC pin. Set JP1 accord-

ingly.

8If AL/CC is set for charge complete, use pushbutton

switch S1 to simulate a logic low from a controller to

indicate a fully charged battery.

Figure 2. DC1812A Basic Setup

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DEMO MANUAL DC1812A

Quikeval interface

The DC1812A can be connected to a DC590 and used

with the QuikEval software. The DC590 connects to a PC

through USB. QuikEval automatically detects the demo

board and brings up the LTC2943 evaluation software

interface (Figure 3).

Interface Design

The QuikEval interface consists of three tabs along with a

column that displays accumulated charge since the start of

the scan, voltage, current and temperature. A start button

allows convenient polling of the registers.

Figure 3. LTC2943 QuikEval Interface

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DEMO MANUAL DC1812A

Quikeval interface

INFO COLUMN

Accumulated Charge Since Start (ACR Display)

The “Accumulated Charge Since Start” text box displays

the change in accumulated charge since the start of a scan.

The initial data in the ACR registers (registers C and D)

is first stored at the start of a scan and then any change

in charge is reported in the ACR text box. This data can

be displayed in one of two formats: coulombs and mAh.

Voltage and Current Display

Data from the voltage ADC (registers I and J) and the

current ADC (registers O and P) is displayed here in volts

and amperes, respectively. If the current falls into the mA

range then the interface automatically updates the units

accordingly. The display indicates the current as seen

from the battery. Hence, if a negative value is displayed,

the battery is discharging. If a positive value is displayed,

the battery is charging.

Temperature Display

Data from the temperature ADC (register U and V) is dis-

played here. It can be displayed in two formats: Celsius

and Kelvin.

Start Button

Click on start to begin a polling routine that is based on

the selected ADC mode. By default the ADC mode is set to

automatic mode which updates the interface every 60ms.

If the scan ADC mode is selected from the “Registers and

Control” tab, then the interface would update every 10s.

The ADC mode can be switched in real time during a scan

and the interface will respond accordingly.

The interface recognizes when it is scanning and replaces

the start button with a stop button during a polling routine.

Similarly, for a single update, select the manual mode

and click start. The LTC2943 will take a snapshot of the

charge, voltage, current and temperature after which it

will immediately go into sleep mode in which only the

charge accumulator is running. For convenience the GUI

will hold the values of the snapshot for 2 seconds before

updating the interface and displaying “ADC Off” in the

current, voltage and temperature text box.

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DEMO MANUAL DC1812A

COULOMB COUNTER TAB

This tab contains time based graphical plots of charge

and current. The charge plot displays the change in ac-

cumulated charge since the start of a scan with respect to

time in mAh or coulombs depending on user input. The

current plot displays the change in current with respect

Quikeval interface

to time in mA. If the current exceeds 1A, then the graph

auto scales to display the current in units of amperes. If

a scan is restarted, the plots start from the beginning. If

manual mode is selected, only the charge plot is active.

Once the plotted line reaches 300, the x-axis scrolls to

accommodate by 30 second intervals.

Figure 4. Coulomb Counter Tab

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DEMO MANUAL DC1812A

Quikeval interface

BATTERY GAUGE TAB

This tab contains controls to set up the battery gas gauge

and consists of two sections: User Input and Initialization.

User Input

For applications that have low current and a large battery, it

is possible to get a qLSB size smaller than QBAT/216, caus-

ing the 16-bit accumulated charge register to underflow

before the battery is exhausted or overflow during charge.

In such cases, RSENSE should be sized according to the

following relationship:

RSENSE ≤0.340mAh •2

QBAT

•50mΩ

Figure 5. Battery Gauge Tab

where QBAT is in mAh. Similarly, for applications with a

small battery but high maximum current the qLSB can get

quite large with respect to the battery capacity causing a

lossindigitalresolution in the accumulated charge register.

To address this, the LTC2943 includes a programmable

prescalar. Lowering the prescalar factor M reduces qLSB

to better match the accumulated charge register to the

capacity of the battery. M can be chosen between 1 and

its default value of 4096. The charge LSB then becomes:

qLSB =0.34mAh •

50m

SENSE

•

4096

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DEMO MANUAL DC1812A

Quikeval interface

To avoidunnecessarycalculation,theinterface conveniently

suggests a prescalar value to use based on the entered

battery capacity and sense resistor value. This prescalar

can be overridden by the user with the help of the prescalar

dropdown box. In the case of an override, the prescalar

dropdown box will be colored red giving a visual cue that

the prescalar chosen is not the suggested one.

The interface also warns the user in case the current is

too small with respect to the battery capacity by giving

an error message similar to the one shown in Figure 6.

Figure 6. Low Current Warning

Figure 7. Battery Gas Gauge

Initializing the Accumulated Charge Register

By default, the ACR register has the initial value of 0x7FFF.

The ACR register can be initialized to full, empty or set to

a user defined level based on battery capacity.

The “From Voltage (Li-ion Only)” button gives an estimate

of the initial ACR value by sensing the voltage and ambient

temperature of the battery being used. It compares the

voltage and temperature values to the discharge curves of

a Panasonic CGR18650CG lithium ion battery to estimate

the battery’s state of charge. Due to the fact that the dis-

charge curve for each lithium ion battery is different, the

state of charge calculated this way might not be accurate.

It is strongly advised to use a characterized battery whose

state of charge is already known and to initialize the ACR

value accordingly.

Battery Gas Gauge

The gas gauge shows the battery’s state of charge. The

upper battery limit is always 0xFFFF while the lower limit

is dependent on the battery capacity and qLSB size. This

lower limit is calculated based off of RSENSE and prescalar

M, and displayed in hexadecimal in the lower right corner

of the gas gauge. Battery charge percentage as well as the

ACR register value is shown alongside the gas gauge. The

amount of charge left is also represented in mAh under

the battery widget.

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DEMO MANUAL DC1812A

Quikeval interface

Figure 8. Register and Control Tab

The register and control tab provides a detailed view of the

LTC2943 device registers as well as provides convenient

means to read and write to them.

Address/I2C Status

The write address for the LTC2943 is C8h and the read

address is C9h. If an error occurs while reading from

the LTC2943, the I2C status will display an error and the

corresponding LED will turn red. Otherwise, the status is

good and the LED remains green.

Sense Resistor

By default, the demo board is populated with a 100mΩ

sense resistor to measure a maximum full-scale current of

500mA. If a different full-scale value current is desired, the

sense resistor can be easily replaced and the correspond-

ing resistor value can be set in the interface. Every time a

new resistor value is entered, the interface will recalculate

a suggested prescalar and qLSB automatically and display

it in the “LSB Information” section.

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DEMO MANUAL DC1812A

Quikeval interface

LSB Information

LSB information for charge, voltage, current and tem-

perature registers as well as for all threshold registers is

displayed here. The ACR LSB updates depending on the

sense resistor and prescalar value chosen.

Status Register (A)

The individual status bits A[0:7] and their states are shown

here. A red indicator next to bits A[6:0] indicates the re-

spective alert is currently present and will latch the alert

pin if conﬁgured for alert. Bit A[7] is reserved.

The demo board alert pin indicator indicates the status of

the AL/CC pin. If the LTC2943 AL/CC pin is set for alert

mode and an alert has been latched, the device will pull

down this pin which will light up the LED indicator on the

board as well as on the GUI. Click on ARA to send out an

SMBus alert on to the bus lines and the device will respond

with its address. The LED indicator on the demo board

and GUI alert pin indicator will then be cleared if the alert

is no longer present.

Control Register (B)

Configurations done in the control register section write

to the control register (register B). The control bits B[7:6]

set the LTC2943 ADC mode. The LTC2943 defaults to

automatic mode which enables full-time voltage, current

and temperature ADC conversions. Selecting scan mode

enables voltage, current and temperature conversions

cycles every 10s. After each conversion cycle the ADC

goes into sleep mode until it is time for the next conver-

sion cycle. Selecting manual mode initiates the ADC for

a snapshot of voltage, temperature, current and charge

once after which it returns to sleep mode. In sleep mode,

the LTC2943 continues to accumulate charge while the

ADC turns off.

Select a prescalar M value to scale the ACR according

to battery capacity and maximum current. M cannot be

changed during a scan.

The AL/CC pin can be conﬁgured for alert mode, charge

complete mode, or disabled. Select the corresponding

settings on the DC1812 jumper JP1.

The shutdown analog section is checked to disable the

analog portion of the LTC2943 and set the device in a

low current state. For normal operation leave unchecked.

Data in the internal registers of the LTC2943 is displayed

here in hexadecimal format. Data can also be entered and

written to the write registers. Enter data to be written in

hexadecimal, or select unit and enter data in decimal form.

Then click on the corresponding register button to write

to that register. Data is auto corrected if the maximum or

minimum full-scale is exceeded.

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DEMO MANUAL DC1812A

parts list

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

1 1 C2 CAP., CHIP X7R, 0.1µF 0603 AVX, 06033C104KAT2A

2 1 C3 CAP., X7R, 1.0µF, 100V, 10%, 1206 MURATA, GRM31CR72A105KA01

3 1 D1 LED, RED, LIGHT EMITTING DIODES PANASONIC, LN1251CTR

4 1 D2 DIODE, BAT54C SOT23 DIODES INC.,BAT54C-7-F

5 4 E1-E4 TURRET, TESTPOINT .094" MILL-MAX, 2501-2-00-80-00-00-07-0

6 5 E5-E9 TURRET, TESTPOINT .064" MILL-MAX, 2308-2-00-80-00-00-07-0

7 1 JP1 HEADER, 3 PIN 1 ROW .079CC SAMTEC, TMM-103-02-L-S

8 1 XJP1 SHUNT, .079" CENTER SAMTEC, 2SN-BK-G

9 1 J1 HEADERS, VERTICAL DUAL 2×7 .079CC MOLEX, 87831-1420

10 1 RSENSE RES., CHIP, 0.1Ω 1/8W 1% 1206 IRC, LRC-LR1206LF-01-R100-F

11 3 R6, R7, R8 RES., CHIP, 4.99k, 1%, 0603 NIC, NRC06J4991TRF

12 4 R2, R3, R4, R9 RES., CHIP, 10k, 5%, 0603 NIC, NRC06J103TRF

13 1 R5 RES., CHIP, 1k, 5%, 0603 VISHAY, CRCW06031K00JNEA

14 1 S1 SWITCH, SMT PUSH BUTTON PANASONIC, EVQPE105K

15 1 U2 I.C., SERIAL EEPROM TSSOP8 MICROCHIP, 24LC025-I/ST

16 1 FOR (J1) CABLE ASSY., 8" STRIP LINEAR RIBBON CABLE CA-2440

17 1 U1 I.C., BATTERY GAS GAUGE WITH I2C LINEAR TECH., LTC2943CDD

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