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参数资料
| 型号： | ADP3802AR |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | 电源管理 |
| 英文描述： | Secondary Over-Voltage Protection for 2-4 cell in series Li-Ion/Poly (4.50V) 8-SM8 -40 to 110 |
| 中文描述： | 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO16 |
| 封装： | SOIC-16 |
| 文件页数： | 17/20页 |
| 文件大小： | 256K |
| 代理商： | ADP3802AR |
ADP3801/ADP3802
–17–
REV. 0
The 60 second wait period allows the output capacitor to dis-
charge before switching from one battery to the next. Without
this wait period, the capacitor would be fully charged when
switched to an uncharged battery. The current under this condi-
tion is only limited by the ESR of the capacitor, the ON resis-
tance of the FET and diode, and the series resistance of the
battery. These values are typically very small, so current in
excess of 5 amps can flow for a short time period. In most
practical circuits the wait period is not required, but it is good
practice to have it in
μ
C controlled systems. The duration of the
wait period is determined by the RC time constant of C
O
and R
B
and can be adjusted by changing these components.
The two Si4463 switches are turned on by connecting their
gates to ground. In a short circuit or overdischarged battery
condition, the switches could be operated in their linear region.
This may result in high power dissipation and excessive die
temperature rise. In
μ
C controlled chargers a simple monitor
routine can reduce the charge current if the battery voltage is
lower than about 2 V. This should not happen under normal
circumstances as the Li-Ion cells are not discharged below
2.5 V/cell.
Low Overhead Charging
For applications where the input supply is less than 2 V higher
than the final battery voltage, the circuit of Figure 32 can be
used. This circuit adds a resistor divider to the input of the
current sense amplifier to increase its common-mode input
voltage range. The value of this resistor divider should divide
down the battery voltage such that the common-mode voltage at
CS+ and CS– is at least 2 V less than the chip’s VCC. The
formula for the ratio is:
R
+
R
R
VCC
V
VBAT
MIN
MAX
2
1
2
2
≤
For example, if VCC
MIN
= 9 V and VBAT
MAX
= 8.4 V, then the
ratio would be 0.833. To provide some headroom for resistor
tolerances and line drops, the actual ratio should be lowered to
0.8. The resistors should be reasonably large to keep the current
drain low. Values of R1 = 20 k
(0.1%) and R2 = 80 k
(0.1%)
work well. A diode is added between the current sense resistor
and the battery to prevent discharging the battery through these
resistors.
ADP3801/
ADP3802
CS+
CS–
R1
20k
V
R1
20k
V
R2
80k
V
R2
80k
V
430pF
R
CS
0.1
V
430pF
Figure 32. Low Overhead Charging
Because the current sense voltage is divided down by these
input resistors, the current sense programming function also
changes. Remember to adjust the programming function by the
same ratio. In this example, the programming function would
become 0.125 V/V. Also, the
EOC
current detection point changes
by the same factor.
An alternative to adding the resistor divider is to use a low side
current sense. The CS+ and CS– inputs have a common-mode
range that extends approximately 300 mV below ground. The
circuit in Figure 33 shows how a low side current sense would
be configured. The current programming function,
EOC
detec-
tion point, and ac performance do not change from the normal
configuration.
Si4463
VCC
DRV
EOC
CS–
CS+
ISET
BATA
BATB
A/B
PROG
ADJ
COMP
GND
SD
RESET
V
ISET
R
CS
40m
V
4.3k
V
4.3k
V
2.2nF
GND
V
IN
VL
0.1
m
F
0.1
m
F
VL
V
BATPROG
210
m
F
ADP3801/ADP3802
2.2nF
Figure 33. Low Side Current Sensing For Low Overhead
Charging
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