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參數資料
| 型號： | bq2945 |
| 廠商： | Benchmark Technology Group |
| 英文描述： | Gas Gauge IC with SMBus Interface(Gas Gauge芯片（帶SMBus 接口）) |
| 中文描述： | 氣體計IC，帶有SMBus接口（電量監(jiān)測計芯片（帶的SMBus接口）） |
| 文件頁數： | 6/32頁 |
| 文件大?。?/td> | 256K |
| 代理商： | BQ2945 |
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Voltage Thresholds
In conjunction with monitoring V
SR
for charge/discharge
currents, the bq2945 monitors the battery potential
through the SB pin.
The voltage potential is deter-
mined through a resistor-divider network per the fol-
lowing equation:
R
R
2.25
4
MBV
5
1
=
where MBV is the maximum battery voltage, R
5
is con-
nected to the positive battery terminal, and R
4
is con-
nected to the negative battery terminal. R
5
/R
4
should be
rounded to the next higher integer. R
5
and R
4
should be
sized so that the voltage at the SB pin (V
SB
) should
never exceed 2.4V.
The battery voltage is monitored for the end-of-
discharge voltages (EDV1 and EDVF) and for alarm
warning conditions. EDV threshold levels are used to de-
termine when the battery has reached an “empty” state.
The bq2945 generates an alarm warning when the bat-
tery voltage exceeds the maximum charging voltage by
5% or if the voltage is below EDVF. The battery voltage
gain, the two EDV thresholds, and the charging voltage
are programmable in the EEPROM.
If V
SB
is below either of the two EDV thresholds, the associ-
ated flag is latched and remains latched, independent of
V
SB
,until the next valid charge.
EDV monitoring may be disabled under certain condi-
tions. If the discharge current is greater than approxi-
mately 6A, EDV monitoring is disabled and resumes af-
ter the current falls below 6A.
Reset
The bq2945 is reset when first connected to the battery
pack. On power-up, the bq2945 initializes and reads the
EEPROM configuration memory. The bq2945 can also
be reset with a command over the SMBus. The software
reset sequence is the following: (1) write MaxError
(0x0c) to 0x0000; (2) write the reset register (0x64) to
0x8009. A software reset can only be performed if the
bq2945 is in an unlocked state as defined by the value in
location 0x3d of the EEPROM (EE 0x3d) on power-up.
Temperature
The bq2945 monitors temperature sensing using an in-
ternal sensor. The temperature is used to adapt charge
and self-discharge compensations as well as to monitor
for maximum temperature and
T/
t during a bq2945
controlled charge. Temperature may also be accessed
over the SMBus with command 0x08.
Layout Considerations
The bq2945 measures the voltage differential between
the SR and V
SS
pins. V
OS
(the offset voltage at the SR
pin) is greatly affected by PC board layout. For optimal
results, the PC board layout should follow the strict rule
of a single-point ground return. Sharing high-current
ground with small signal ground causes undesirable
noise on the small signal nodes. Additionally, in refer-
ence to Figure 1:
The capacitors (C1 and C2) should be placed as close as
possible to the SB and V
CC
pins, and their paths to V
SS
should be as short as possible. A high-quality ceramic
capacitor of 0.1
μ
f is recommended for V
CC
.
The sense resistor capacitor (C3) should be placed as
close as possible to the SR pin.
The bq2945 should be in thermal contact with the
cells for optimum temperature measurement.
An optional zener (D9) may be necessary to ensure that
V
CC
is
not
above
the
operation.
maximum
rating
during
Gas Gauge Operation
The operational overview diagram in Figure 2 illus-
trates the operation of the bq2945. The bq2945 accumu-
lates a measure of charge and discharge currents, as
well as an estimation of self-discharge. Charge currents
are compensated for temperature and state-of-charge of
the battery. Self-discharge is temperature-compensated.
The main counter, RemainingCapacity (RM), represents
the available battery capacity at any given time. Battery
charging increments the RM register, whereas battery dis-
charging and self-discharge decrement the RM register
and increment the internal Discharge Count Register
(DCR).
The Discharge Count Register is used to update the
FullChargeCapacity (FCC) register only if a complete
battery discharge from full to empty occurs without any
partial battery charges. Therefore, the bq2945 adapts
its capacity determination based on the actual condi-
tions of discharge.
The battery's initial full capacity is set to the value stored
in EE 0x60-0x61. Until FCC is updated, RM counts up to,
butnotbeyond,thisthresholdduringsubsequentcharges.
1.
FullChargeCapacity or learned-battery
capacity:
FCC is the last measured discharge capacity of the
battery. On initialization (application of V
CC
or reset),
FCC is set to the value stored in the EEPROM. Dur-
ing subsequent discharges, FCC is updated with the
6
bq2945
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相關代理商/技術參數 |
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| BQ294502 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Overvoltage Protection for 2-Series and 3-Series Cell Li-Ion Batteries |
| BQ294502DRVR | 功能描述:電池管理 Overvltg Prot Device RoHS:否 制造商:Texas Instruments 電池類型:Li-Ion 輸出電壓:5 V 輸出電流:4.5 A 工作電源電壓:3.9 V to 17 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:VQFN-24 封裝:Reel |
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