DEMO MANUAL DC1812A
LTC2943/LTC2943-1/LTC2944
Multicell Battery Gas Gauge with Temperature,
Voltage and Current Measurement
Description
Demonstration circuit 1812A-A (Figure 1) features the
LTC
®
2943.
Demonstration circuit 1812A-B features the
LTC2944.
Demonstration circuit 1812A-C features the
LTC2943-1.
The LTC2943/LTC2943-1 has an operating
range of 3.6V to 20V, while the LTC2944 has an operating
range of 3.6V to 60V, making all three devices perfectly
suited for multicell battery applications. 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/LTC2943-1 measures
voltage, current and temperature with an internal 14-bit
No Latency ∆∑™ ADC. The LTC2944 measures voltage,
current and temperature with an internal 16-bit No Latency
∆∑ ADC. The measurements are stored in internal registers
accessible via the onboard SMBus/I
2
C interface.
The LTC2943/LTC2943-1/LTC2944 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.
The LTC2943 and LTC2944 require only a single low
value sense resistor to set the measured current range.
The LTC2943-1, however, has an integrated sense resistor
of 50mΩ which sets the maximum current measurement
to 1A. The default value assembled on the DC1812A-A and
DC1812A-B is 100mΩ for a maximum current measure-
ment of 500mA. The DC1812A-C which showcases the
LTC2943-1 has the onboard sense resistor omitted in favor
of the integrated 50mΩ sense resistor. All three parts have
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 or DC2026.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1812A
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.
Figure 1. DC1812A
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DEMO MANUAL DC1812A
Quick start proceDure
Demonstration circuit 1812A is easy to set up to evaluate
the performance of the LTC2943/LTC2943-1/LTC2944.
Refer to Figure 2 for proper measurement equipment
setup and follow the procedure below.
1. Connect a Li-Ion battery across V_BAT and GND. Mul-
tiple Li-Ion batteries can also be used as long as the
total voltage does not exceed the operating voltage of
the device. The LTC2943/LTC2943-1 has a maximum
operating voltage of 20V, so for a 4.2V lithium ion
battery the maximum cell count would be 4 cells. The
LTC2944 has a maximum operating voltage of 60V, so
for a 4.2V lithium-ion battery the maximum cell count
would be 14 cells.
2. Connect a load across V_CHRG/LD and GND for battery
discharge measurement.
3. Connect 3.6V to 20V (LTC2943/LTC2943-1) or
3.6V to 60V (LTC2944) battery charger supply
across V_CHRG/LD and GND for battery charge mea-
surement. Up to 500mA supplied to the battery can
be measured with the board default 100mΩ sense
resistor present on the DC1812A-A and DC1812A-B.
The DC1812A-C can support currents of up to 1A with
its integrated 50mΩ 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 I
2
C bus to
the SDA, SCL and GND test turrets.
5. If a host I
2
C controller is 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/LTC2943-1/LTC2944
through I
2
C.
7. Through I
2
C, configure the
AL/CC
pin. Set JP1 accord-
ingly.
8 If
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
Figure 3. 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/LTC2944 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.
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.
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DEMO MANUAL DC1812A
Quikeval interface
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/LTC2943-1/LTC2944 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.
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
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.
Figure 4. Coulomb Counter Tab
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DEMO MANUAL DC1812A
Quikeval interface
Once the plotted line reaches 300, the x-axis scrolls to
accommodate by 30 second intervals.
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 q
LSB
size smaller than Q
BAT
/2
16
, caus-
ing the 16-bit accumulated charge register to underflow
before the battery is exhausted or overflow during charge.
In such cases, R
SENSE
should be sized according to the
following relationship:
0.340mAh
•
2
16
R
SENSE
≤
•
50mΩ
Q
BAT
where Q
BAT
is in mAh. Similarly, for applications with a small
battery but high maximum current the q
LSB
can get quite
large with respect to the battery capacity causing a loss
in digital resolution in the accumulated charge register. To
address this, the LTC2943/LTC2943-1/LTC2944 includes
a programmable prescalar. Lowering the prescalar factor
M reduces q
LSB
to better match the accumulated charge
Figure 5. Battery Gauge Tab
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PCB Design
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