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参数资料
| 型号： | DC1496B-B |
| 厂商： | Linear Technology |
| 文件页数： | 11/18页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL LTC2942 |
| 软件下载： | QuikEval System |
| 设计资源： | DC1496B Design Files |
| 标准包装： | 1 |
| 系列： | QuikEval™ |
| 主要目的： | 电源管理，燃料量计 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | LTC2942 |
| 主要属性： | I²C、SMBus 接口 |
| 次要属性： | LED 状态指示器 |
| 已供物品： | 板，线缆 |
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LTC2942
APPLICATIONS INFORMATION
q LSB = 0.085mAh ?
50m ? M
Q BAT R SENSE
M ≥ 128 ? ?
? 0.085mAh 50m ?
2
ChoosingCoulombCounterPrescalerMB[5:3]
If the battery capacity (Q BAT ) is very small compared to
the maximum current (I MAX ) (Q BAT < I MAX ? 0.1 Hours)
the prescaler value M should be changed from its default
value (128).
In these applications with a small battery but a high
maximum current, q LSB can get quite large with respect
to the battery capacity. For example, if the battery capacity
is 100mAh and the maximum current is 1A, the standard
equation leads to choosing a sense resistor value of
50mΩ, resulting in:
q LSB = 0.085mAh = 306mC
The battery capacity then corresponds to only 1176 q LSB s
and less than 2% of the accumulated charge register is
utilized.
To preserve digital resolution in this case, the LTC2942
includes a programmable prescaler. Lowering the pres-
caler factor M allows reducing q LSB to better match the
accumulated charge register to the capacity of the battery.
The prescaling factor M can be chosen between 1 and its
default value 128. The charge LSB then becomes:
?
R SENSE 128
To use as much of the range of the accumulated charge
register as possible the prescaler factor M should be
chosen for a given battery capacity Q BAT and a sense
resistor R SENSE as:
16
M can be set to 1, 2, 4, 8, … 128 by programming B[5:3] of
the control register as M = 2 (4 ? B[5] + 2 ? B[4] + B[3]) . The default
value after power up is M = 128 = 2 7 (B[5:3] = 111).
In the above example of a 100mAh battery and an R SENSE
of 50mΩ, the prescaler should be programmed to M = 4.
The q LSB then becomes 2.656μAh and the battery capacity
corresponds to roughly 37650 q LSB s.
Note that the internal digital resolution of the coulomb
counter is higher than indicated by q LSB . The digitized
charge q INTERNAL is M ? 8 times smaller than q LSB . q INTERNAL
is typically 299μAs for a 50mΩ sense resistor.
ADC Mode B[7:6]
The LTC2942 features an ADC which measures either
voltage on SENSE – (battery voltage) or temperature via
an internal temperature sensor. The reference voltage and
clock for the ADC are generated internally.
The ADC has four different modes of operation, as shown
in Table 3. These modes are controlled by bits B[7:6] of
the control register. At power-up, bits B[7:6] are set to
[00] and the ADC is in sleep mode.
A single voltage conversion is initiated by setting the bits
B[7:6] to [10]. A single temperature conversion is started
by setting bits B[7:6] to [01]. After a single voltage or
temperature conversion, the ADC resets B[7:6] to [00]
and goes to sleep.
The LTC2942 also offers an automatic scan mode where
the ADC converts voltage, then temperature, then sleeps
for approximately two seconds before repeating the voltage
and temperature conversions. The LTC2942 is set to this
automatic mode by setting B[7:6] to [11] and stays in this
mode until B[7:6] are reprogrammed by the host.
Programming B[7:6] to [00] puts the ADC to sleep. If
control bits B[7:6] change within a conversion, the ADC
will complete the current conversion before entering the
newly selected mode.
A conversion of either voltage or temperature requires 10ms
conversion time (typical). At the end of each conversion,
the corresponding registers are updated. If the converted
quantity exceeds the values programmed in the threshold
registers, a flag is set in the status register and the AL /CC
pin is pulled low (if alert mode is enabled).
During a voltage conversion, the SENSE – pin is connected
through a small resistor to a sampling circuit with an
equivalent resistance of 2MΩ, leading to a mean input
current of I = V SENSE– /2MΩ.
2942fa
11
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| DC1496B-B | 制造商:Linear Technology 功能描述:EVAL BOARD, LTC2942 BATTERY FUEL GAUGE |
| DC1496B-C | 制造商:Linear Technology 功能描述:BOARD EVAL FOR LTC2941-1 制造商:Linear Technology 功能描述:LTC2941-1 BATTERY GAS GAUGE 制造商:Linear Technology 功能描述:DEMO BOARD, LTC2941IDCB-1 BATTERY GAS GAUGE; Silicon Manufacturer:Linear Technology; Silicon Core Number:LTC2941; Kit Application Type:Power Management; Application Sub Type:Fuel Gauge; Kit Contents:Demo Board LTC2941 |
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