Linear Technology DC1812A Quick setup guide

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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
16
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
Ω
R
SENSE
•
M
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
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.
Register Read/Write
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