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參數(shù)資料
| 型號(hào)： | ADP3801 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | High Frequency Switch Mode Dual Li-Ion Battery Chargers(高頻開關(guān)模式雙鋰離子充電器) |
| 中文描述： | 高頻開關(guān)雙鋰離子電池充電器（高頻開關(guān)模式雙鋰離子充電器） |
| 文件頁數(shù)： | 10/20頁 |
| 文件大小： | 278K |
| 代理商： | ADP3801 |
ADP3801/ADP3802
–10–
REV. 0
Current Sense Amplifier
A differential, high side current sense amplifier (GM1 in Figure
20) amplifies the voltage drop across a current sense resistor
R
CS
. The input common-mode range of GM1 extends from
ground to VCC – 2 V. Sensing to ground ensures current regu-
lation even in short circuit conditions. To stay within the com-
mon-mode range of GM1, VCC must be at least 2 V greater
than the final battery voltage or a circuit such as shown in Fig-
ure 32 must be used. RC filters are included to filter out high
frequency transients, which could saturate the internal circuitry.
The filter’s cutoff is typically set at half the switching frequency
of the oscillator.
The charge current is controlled by the voltage on the ISET pin
according to the following formula:
I
V
R
CHARGE
ISET
×
CS
=
10
The factor of 10 is due the GM1’s gain of 10 V/V. To set a charge
current of 1.5 A with R
CS
= 0.1
, V
ISET
must be 1.5 V. Figure
22 shows the linearity of the charge current control as the volt-
age is increased from 0 V to the programmed final battery volt-
age (12.6 V in this case). It is important to state that this curve
is taken with an ideal, zero impedance load. An actual Li-Ion
battery will exhibit a more gradual drop in charge current due to
the internal impedance of the battery as shown in Figure 25.
V
OUT
– Volts
0
2
3
I
C
4
5
6
7
8
9
10
0.5
11
12
13
1.0
1.5
2.0
2.5
3.0
3.5
Figure 22. CCCV Characteristic with Ideal Load
Overcurrent Comparator
Similar to the voltage loop, the current loop includes a com-
parator to protect the external circuitry from an overcurrent
event. This comparator trips when GM1’s differential input
voltage exceeds 185 mV. Like the overvoltage comparator, it has
two outputs to quickly reduce the duty cycle to 0% and to pro-
vide a soft-start recovery. The response time of the internal
comparator is approximately 1
μ
s; however, the filter on the
input of GM1 may slow down the total response time of the
loop.
End-of-Charge Output
The ADP3801/ADP3802 provides an active low, end-of-charge
(
EOC
) logic output to signal when the battery has completed
charging. The typical Li-Ion charging characteristic in Figure 25
shows that when the battery reaches its final voltage the current
decreases. To determine
EOC
, an internal comparator senses
when the current falls below 6% of full scale, ensuring that the
battery has been fully charged. The comparator has hysteresis to
prevent oscillation around the trip point.
To prevent false triggering (such as during soft-start), the com-
parator is only enabled when the battery voltage is within 5% of
its final voltage. As the battery is charging up, the comparator
will not go low even if the current falls below 6% as long as the
battery voltage is below 95% of full scale. Once the battery has
risen above 95%, the comparator is enabled.
There are two important reasons for this functionality. First,
when the circuit is initially powered on, the charge current is
zero because of the soft start. If the comparator is not gated by
the battery voltage, then
EOC
would go low erroneously. Sec-
ond, a provision must be made for battery discharge. Assume
that a battery has been fully charged.
EOC
goes low, and the
charger is gated off. When the battery voltage falls to 95%, due
to self-discharge for example,
EOC
will return high. Then the
charger can start up and top off the battery, preventing the
battery from “floating” at the end-of-charge voltage.
The
EOC
output has many possible uses as shown in Figure 23.
One simple function is to terminate the charging to prevent
floating (Figure 23a). It can be used as a logic signal to a
microcontroller to indicate that the battery has finished charg-
ing. The microcontroller can then switch to the next battery if
appropriate or shutdown the ADP3801/ADP3802. It can also be
used to turn on an LED to signal charge completion (Figure
23b). Using a flip-flop,
EOC
can control the switching from
BATA to BATB (Figure 23d). The RC filter delays switching
between the two batteries to ensure that the output capacitor is
discharged.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADP38010001RR | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADP3801AR | 制造商:Analog Devices 功能描述: |
| ADP3801AR-REEL | 制造商:Rochester Electronics LLC 功能描述:SWITCH MODE DUAL CHARGER/LDO REGULATOR - Tape and Reel |
| ADP3802 | 制造商:AD 制造商全稱:Analog Devices 功能描述:High Frequency Switch Mode Dual Li-Ion Battery Chargers |
| ADP3802AR | 制造商:AD 制造商全稱:Analog Devices 功能描述:High Frequency Switch Mode Dual Li-Ion Battery Chargers |
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