参数资料
型号: LTC4071IMS8E#PBF
厂商: Linear Technology
文件页数: 8/18页
文件大小: 0K
描述: IC LI-ION/POLY BATT CHRGR 8-MSOP
标准包装: 50
功能: 充电管理
电池化学: 锂离子(Li-Ion)、锂聚合物(Li-Pol)
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 8-TSSOP,8-MSOP(0.118",3.00mm 宽)裸露焊盘
供应商设备封装: 8-MSOP-EP
包装: 管件
LTC4071
OPERATION
In cases where the input supply may be shorted to GND
when not supplying power, for example with a solar cell, add
a diode in series with R IN to prevent the input from loading
the battery. For more information, refer to the photovoltaic
charger example in the Applications Information section.
Adjustable Float Voltage, V FLOAT
A built-in 3-state decoder connected to the ADJ pin pro-
vides three programmable float voltages: 4.0V, 4.1V, or
4.2V. The float voltage is programmed to 4.0V when ADJ
is tied to GND, 4.1V when ADJ is floating (disconnected),
and 4.2V when ADJ is tied to V CC . The state of the ADJ
pin (and NTC pins) is sampled for about 36μs about once
every 1.2 seconds when HBO is high, and when HBO is
low the sampling rate reduces to about once every 3.6
seconds with the same duty cycle. If V CC falls below
V LBD , the sampling stops. When it is being sampled, the
LTC4071 applies a relatively low impedance voltage at the
ADJ pin. This technique prevents low level board leakage
from corrupting the programmed float voltage.
NTC Qualified Float Voltage, ?V FLOAT(NTC)
The NTC pin voltage is compared against an internal
resistor divider tied to the NTCBIAS pin. This divider has
tap points that are matched to the NTC thermistor resis-
tance/temperature conversion table for a Vishay curve 2
thermistor at temperatures of 40°C, 50°C, 60°C, and 70°C.
The curve 2 thermistor is also designated by a B25/85
value of 3490.
Battery temperature conditioning adjusts the float voltage
down to V FLOAT_EFF when the NTC thermistor indicates
that the battery temperature is too high. For a 10k curve 2
thermistor and a 10k NTCBIAS resistor, each 10°C increase
in temperature above 40°C causes the float voltage to drop
by a fixed amount, ?V FLOAT(NTC) , depending on ADJ. If ADJ
is at GND, the float voltage steps down by 50mV for each
10°C temperature increment. If ADJ is floating, the step
size is 75mV. And if ADJ is at V CC , the step size is 100mV.
Refer to Table 1 for the range of V FLOAT_EFF programming.
Table 1 . NTC Qualified Float Voltage
V NTC AS % OF
ADJ ?V FLOAT(NTC) TEMPERATURE NTCBIAS V FLOAT_EFF
GND 50mV T < 40°C V NTC > 36.5 4.000
40°C ≤ T < 50°C 29.0 < V NTC ≤ 36.5 3.950
50°C ≤ T < 60°C 22.8 < V NTC ≤ 29.0 3.900
60°C ≤ T < 70°C 17.8 < V NTC ≤ 22.8 3.850
70°C < T V NTC ≤ 17.8 3.800
Floating 75mV T < 40°C V NTC > 36.5 4.100
40°C ≤ T < 50°C 29.0 < V NTC ≤ 36.5 4.025
50°C ≤ T < 60°C 22.8 < V NTC ≤ 29.0 3.950
60°C ≤ T < 70°C 17.8 < V NTC ≤ 22.8 3.875
70°C < T V NTC ≤ 17.8 3.800
V CC 100mV T < 40°C V NTC > 36.5 4.200
40°C ≤ T < 50°C 29.0 < V NTC ≤ 36.5 4.100
50°C ≤ T < 60°C 22.8 < V NTC ≤ 29.0 4.000
60°C ≤ T < 70°C 17.8 < V NTC ≤ 22.8 3.900
70°C < T V NTC ≤ 17.8 3.800
For all ADJ pin settings the lowest float voltage setting is:
3.8V = V FLOAT_MIN = V FLOAT – 4 ? ?V FLOAT(NTC) .
This occurs at NTC thermistor temperatures above 70°C,
or if the NTC pin is grounded.
To conserve power in the NTCBIAS and NTC resistors, the
NTCBIAS pin is sampled at a low duty cycle at the same
time that the ADJ pin state is sampled.
High Battery Status Output: HBO
The HBO pin pulls high when V CC rises to within V HBTH
of the programmed float voltage, V FLOAT_EFF , including
NTC qualified float voltage adjustments assuming V CC
has risen above V LBC_VCC .
If V CC drops below the float voltage by more than V HBTH +
V HBHY the HBO pin pulls low to indicate that the battery is
not at full charge. The input supply current to the LTC4071
drops to less than 550nA (typ) as the LTC4071 no longer
shunts current to protect the battery. And the NTCBIAS
sample clock slows to conserve power.
For example, if the NTC thermistor requires the float voltage
to be dropped by 100mV (ADJ = V CC and 0.29 ?V NTCBIAS
< V NTC < 0.36 ?V NTCBIAS ) then the HBO rising threshold
is detected when V CC rises past:
V FLOAT – ?V FLOAT(NTC) – V HBTH
= 4.2V – 100mV – 40mV = 3.96V.
4071fc
8
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