Download How to Operate bq20z7x/8x/9x Fuel Gauge and

Application Report
SLUA608 – August 2011
How to Operate bq20z7x/8x/9x Fuel Gauge and
bq24707/25/26 Charger Without Host Controller
Tahar Allag/Wang Li
...................................................................................... PMP BMS Battery Charge
ABSTRACT
The bq24707/26/25 chargers and the bq20z7x/8x/9x gas gauges are both SBS-compliant integrated
circuits. In this application report, both of these chargers and gas gauges are used together as a
nonhost-control, battery charging system. An external regulator, TPS7A49xx, is added to the system to
prevent shutting down the system during a deeply discharged state of the battery cells. It provides a
wake-up current to charge the discharged battery cells and power up the system. This document
describes the system in detail and provides the test results.
1
Descriptions
1.1
bq24707/25/26
The bq24707/25/26 is a highly efficient, synchronous, battery-charger family designed for multichemistry
batteries. The integrated circuit (IC) operates as a slave, where it receives control inputs externally from
the embedded controller host through the SMBus interface. The SMBus-controlled input current, charge
voltage, and charge current provide high regulation accuracies that can be programmed externally using a
system power management microcontroller. In this application report, the gas gauge is used to operate as
a master, and the charger receives the controlled input from the gas gauge through the SMBus.
1.2
bq20z7x/8x/9x
The bq20z7x/8x/9x, SBS-compliant gas gauge IC, incorporating patented Impedance Track™ technology,
is designed for battery-pack or in-system installation. It measures and maintains an accurate record of
available charge in Li-ion or Li-polymer batteries using its integrated high-performance analog peripherals.
It monitors capacity change, battery impedance, open-circuit voltage, and other critical parameters of the
battery pack, and reports the information to the system host controller over a SMBus.
1.3
TPS7A49xx
The TPS7A49xx is a series of devices that is positive, high-voltage (up to 36 V), ultralow-noise, linear
regulator that is capable of sourcing a load of 150 mA. It is suited for post dc-dc converter regulation. It
has an option to adjust the output voltage from 1.194 V to 33 V using external resistors tied in series with
the output and the feedback pin. One of the primary uses of this linear regulator is to provide ultralow
noise on a voltage rail at a fixed output voltage. In this application report, the TPS7A49xx is used to revive
the deeply discharged battery cell to allow proper operation of the gas gauges and the entire system.
2
Implementations
The charge IC (bq24707/25/26) and gas gauge IC (bq20z7x/8x/9x) are both SBS compliant. The charger
IC operates as a slave. Control input is received from the gas gauge IC through the SMBus. The gas
gauge IC operates as master with broadcasts enabled. It broadcasts the ChargeCurrent() and
ChargeVoltage() command to the charger IC. The ChargeCurrent() register address is 0x14 and the
ChargerVoltage() register address is 0x15. When the charger IC gets the two commands, it starts the
Impedance Track is a trademark of Texas Instruments.
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How to Operate bq20z7x/8x/9x Fuel Gauge and bq24707/25/26 Charger Without
Host Controller
Copyright © 2011, Texas Instruments Incorporated
1
Implementations
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charger. In this system, no extra host controller is required for the charger IC. It saves the total cost of the
total system software resource. However, an external linear regulator is required for keeping the system
on during low state of charge of the battery cells. When the battery cells are deeply discharged, the linear
regulator provides a wake-up current to bring the cell voltage up and power up the bq20z90/80/70 gas
gauge.
This application report gives an example of using bq24707 and bq20z90 together as a nonhost-control,
battery-charging system solution with a combination of linear regulator TPS7A49xx. The bq24726
evaluation module (HPA3558), and the bq20z90 evaluation module (HPA155) are used for this
demonstration.
Figure 1. bq24726, TPS7A49xx and bq20z90 EVMs Constitute a Nonhost-Control, SMBus Charger System
Figure 1 shows a two-EVM connection for the nonhost control SMBus charger system. The following steps
show how the Figure 1 test setup can be constructed.
Step 1. bq24726EVM Setup:
2
How to Operate bq20z7x/8x/9x Fuel Gauge and bq24707/25/26 Charger Without
Host Controller
Copyright © 2011, Texas Instruments Incorporated
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Test Result
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1.
2.
3.
4.
Connect ACDET to BAT in JP1.
Connect VCC to BAT in JP3.
Connect EXT to DPM in JP2.
The 3.3-V output of the TPS7A4901 must be connected to the J3-3V3 of the bq24726EVM.
Step 2. bq20z90EVM Configuration:
1. Enable the bcast bit in DF. This bit is in one of the Operation CFG DF locations.
2. Ensure that HPE or CPE bits are set in the in DF because the charger does not use PEC.
3. Add a short jumper between TB4-SYS PRES and TB3-GND.
4. Add three battery cells in series among 1N, 1P, 2P, and 3P. Also, short jumper between 3P and 4P.
Step 3.
The TPS7A4901 needs to be adjusted to output 3.3 V and 6 V. Then connect bq24726, bq20z90,
TPS7A4901, and the power supply together as follows:
1. Connect input power supply only to bq24726EVM J1, and adjust the power supply from 18 V to 24 V.
2. Connect the power supply to the input of the TPS7A4901EVM.
3. Connect the 3.3-V output of the TPS7A4901 to J3-3V3 on the bq24726EVM.
4. Connect the other 6-V TPS7A4901 to a Schottky diode; the output of the diode must be connected to
Pack+-TB4.
5. Connect the SMbus wires between the bq24765EVM and the bq20z80EVM.
bq24726EVM
J4-GND
J4-SCL
J4-SDA
bq20z90EVM
J1-Vss
J1-SMBC
J1_SMBB
6. Connect the bq24726EVM’s BAT output to bq20z90 EVM’s pack termination.
bq24726EVM
J10-GND
J10-BAT
3
bq20z90EVM
TB4-PACK–
TB1-PACK+
Test Result
A 19-V power supply is used to supply both the bq24726 charger and the TPS7A49 regulators. Three
battery cells are connected in series to the gas gauge bq29z726EVM. Figure 2 shows the controlled
signals; the controlled battery voltage is regulated to the desired level.
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How to Operate bq20z7x/8x/9x Fuel Gauge and bq24707/25/26 Charger Without
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Test Result
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Figure 2. SMBUS Control Signal With a Regulated V-bat and System Output
Figure 3 shows the test result for the combined gas gauge with the charger but without the additional
3.3-V and 6-V regulator. As the battery voltage drops below 6 V, the gas gauge shuts down. This causes
the entire system to fail because no control signal is sent from the bq20x90 to the charger. To avoid such
scenarios, an additional regulator is added to the system to prevent the system from failing during deeply
discharged battery cells. Also the bq24726 requires a 3.3-V reference source; another 3.3-V regulator is
added as shown in Figure 1.
4
How to Operate bq20z7x/8x/9x Fuel Gauge and bq24707/25/26 Charger Without
Host Controller
Copyright © 2011, Texas Instruments Incorporated
SLUA608 – August 2011
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Test Result
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Figure 3. Test Result for System Without TPS7A49 6-V Regulator
Conclusion
This application report explains the use of a TI nonhost-control, SMBus, battery-charging system solution.
This solution consists of using the bq24707/25/26 and bq20z90/80/70 together with a combination of linear
regulator TPS7A49xx.
References
1. How to Operate Fuel Gauge bq20z7x/8x/9x and the SMBus-Like Smart Chargers bq24747/765 Without
a Host Controller application report (SLUA533)
2. TPS7A49xx, +36V, +150mA, Ultralow-Noise, Positive LIinear Regulator data sheet ( SBVS121)
3. bq20z80EVM-001 SBS1.1 Impedance Track™ Technology Enabled Battery Management Solution
Evaluation Module user's guide (SLUU234)
SLUA608 – August 2011
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How to Operate bq20z7x/8x/9x Fuel Gauge and bq24707/25/26 Charger Without
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Copyright © 2011, Texas Instruments Incorporated
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