ST STEVAL-ISQ008V1 User manual

September 2010 Doc ID 15176 Rev 1 1/28
UM0612
User manual
STEVAL-ISQ008V1, fuel gauge implementation
based on the STM32F103x
Introduction
This user manual describes the functions of a single cell Li-Ion battery fuel gauge
technology using an MCU within the STM32 (ARM Cortex™-M3 core) family. The fuel gauge
demonstration board is used to show the capability of an STM32 microcontroller to be used
for battery fuel capacity monitoring. The fuel gauge implementation is based on the STM32
microcontroller; the MCU is used for monitoring the capacity of a single cell Li-Ion battery.
An on-chip 12-bit ADC from the STM32 family is used for battery capacity calculation.
The fuel gauge technology is a smart system which monitors battery capacity, predicts
remaining capacity, and displays its status. The basic ideology used for battery capacity
measurements is Coulomb counting, in which the current flowing through the battery is
continuously monitored and integrated to calculate the capacity. Current measurement is
done when the battery is both discharging and charging. Therefore both the IN and OUT
current are taken into account to calculate the remaining capacity of the battery. Battery
capacity is measured in mAh.
Figure 1. STEVAL-ISQ008V1, fuel gauge demonstration board
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Contents UM0612
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Contents
1 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1 Package contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Power supply unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1 Battery supplied block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2 External supplied block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Fuel gauge application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 Demonstration board sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Microcontroller section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.2 Operational amplifier section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.3 Battery charger section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.4 LCD display section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Starting the fuel gauge application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Battery state of health not known . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Battery state of health is known . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.3 Alarm condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.4 LCD messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Compensations in fuel gauge calculations . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.1 Temperature compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.2 Self-discharge compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3 Flow chart for fuel gauge demonstration board . . . . . . . . . . . . . . . . . . 15
4 The STM32 as fuel gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1 ADC error minimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1.1 Dual polarity measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1.2 Amplification of low voltage values . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5 Demonstration board schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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7 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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List of tables UM0612
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List of tables
Table 1. Power selection jumper positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 2. Jumper J4 connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 3. Battery capacity variation due to temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 4. Self-discharge rate of Li-Ion battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 5. BOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 6. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Table 7. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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UM0612 List of figures
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List of figures
Figure 1. STEVAL-ISQ008V1, fuel gauge demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figure 2. Connector for battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 3. External supply selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 4. Charging and discharging path selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 5. Capacity learning for the first time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 6. Flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 7. Microcontroller section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 8. Power section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 9. OP-AMP-section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 10. USB section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 11. LCD section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 12. JTAG-CONN section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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Getting started UM0612
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1 Getting started
1.1 Package contents
The fuel gauge package comes with hardware and supporting documentation.
●Hardware: one demonstration board (along with onboard battery charger)
●Documentation: user manual for operating the demonstration board
1.2 Hardware description
The fuel gauge demonstration board has onboard charging and discharging capabilities.
Major onboard components are:
●STM32F103C8, 32-bit microcontroller
●TS941B, operational amplifier
●L6924D, battery charger
●LD1086XX33, voltage regulator
●STLQ50XX25, voltage reference
●STT5PF20V, P-channel MOSFET
●16 x 2 alphanumeric LCD
●Mini USB connector
●External power supply adapter jack
●100 mΩsense resistor
1.3 Power supply unit
The power supply unit for the demonstration board is divided into two blocks:
1.3.1 Battery supplied block
This block is powered up using the battery supply.
The battery used for capacity monitoring is also used for supplying the load (if resistance
connected at J8).
There is a jumper connection (J3) used for connecting the positive and negative terminal of
the battery. Battery connections are shown in Figure 2. Therefore during the charging of the
battery the current is flowing from the charger to the battery and then through the 100 mΩ
sense resistor. During discharge, current is flowing from the battery through the externally
connected resistance connected at J8 and through the 100 mΩsense resistor.
Voltage drop across the 100 mΩsense resistor is used to evaluate the capacity of the
battery.This voltage drop is measured by ADC of the STM32 MCU and from this measured
voltage, the battery current is calculated.
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UM0612 Getting started
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Figure 2. Connector for battery
1.3.2 External supplied block
External 5 V of power is used for supplying the following components:
●Battery charger
●Back light of LCD
●LCD display.
Note: 1 The DC adapter used for external power should be of 5 V
2 The USB Connector is used for external power supply source only.
Table 1. Power selection jumper positions
Switch jumper SW2 Action
PIN 1 and 2 shorted USB power supply selected
PIN 2 and 3 shorted External DC power source selected
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Getting started UM0612
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Figure 3. External supply selection
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UM0612 Fuel gauge application
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2 Fuel gauge application
This fuel gauge demonstration board is based on the calculation of current flowing through
the 100 mΩsense resistor using the on-chip 12-bit ADC of the STM32 32-bit MCU. The
voltage drop across the sense resistor is measured by the on-chip 12-bit ADC at periodic
intervals of 1 second and this voltage is used for current calculation from which battery
capacity is derived. The current accuracy for this solution is up to +/- 3 mA.
2.1 Demonstration board sections
The fuel gauge demonstration board is split into 4 sections:
●Microcontroller
●Operational amplifier
●Battery charger
●LCD display.
2.1.1 Microcontroller section
The STM32 microcontroller is used for fuel gauge calculations. The features of the STM32
used for this application are:
1. On-chip ADC used for voltage, current, and temperature measurements
2. On-chip RTC used for the time base for fuel gauge computations
3. Input/output ports used for the LCD display
NTC is also connected to one ADC channel of the microcontroller for monitoring battery
temperature.
2.1.2 Operational amplifier section
The TS941BIDT operational amplifier is used as an amplifier and for dual polarity detection
of current flowing through the battery. Input to the operational amplifier is the voltage drop
across the 100 mΩsense resistor and output of the operational amplifier is connected to the
ADC input channel of the microcontroller. Both positive current (in case of battery charging)
and negative current (in case of battery discharging) is measured using this operational
amplifier.
2.1.3 Battery charger section
The L6924 present on the demonstration board is used for charging the battery. Jumper J4
is used for connecting the battery to the resistive load or to the battery charger, as described
in Ta b l e 2 .
Table 2. Jumper J4 connections
Jumper J4 Action
PIN 1 and 2 shorted Battery connected to battery charger
PIN 2 and 3 shorted Battery connected to load at jumper J8
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Fuel gauge application UM0612
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The charger supplies current to the microcontroller circuit and also to the battery, maximum
charging time is fixed at 4 hours. The charger can be powered up either from an external DC
adapter (5 V) or using USB power (shown in Figure 3). Jumper J5 is used for the shutdown
pin of the charger, it should be shorted using the jumper to enable the charger. There are 2
LED's present on the demonstration board (D4 and D5). When charging, the ongoing D4 is
in the OFF state and D5 is in the ON state.
If charging time has lapsed or the battery is not connected to the charger then both D4 and
D5 are in the ON state. Figure 4 shows jumper J4 for selecting the charging and discharging
path.
Figure 4. Charging and discharging path selection
2.1.4 LCD display section
An alphanumeric (16 x 2) LCD is present on the demonstration board. It displays the voltage
of the battery and current flowing through (in/out) the battery. Also the capacity of the battery
is shown as a percentage of full capacity.
If the battery voltage goes below 3.1 V, the “Battery Low” message is displayed on the LCD
and the D2 LED starts blinking.
2.2 Starting the fuel gauge application
The demonstration board has the provision of learning the capacity of a new battery (if not
previously known) or if the user is confident that the new battery is fully charged then the
capacity learning phase can be skipped, but in this case the battery state is considered as
fully charged with a remaining capacity of 900 mAh.
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