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參數(shù)資料
| 型號： | ADP3802AR |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 電源管理 |
| 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 |
| 封裝： | SOIC-16 |
| 文件頁數(shù)： | 9/20頁 |
| 文件大?。?/td> | 256K |
| 代理商： | ADP3802AR |
ADP3801/ADP3802
–9–
REV. 0
Adjusting the Final Battery Voltage
In addition to the PROG input, the ADP3801/ADP3802 pro-
vides an input (ADJ) for fine adjustment of the final battery
voltage. For example, the ADJ amplifier allows the nominal
4.2 V per cell setting for Li-Ion battery cells to be adjusted to
4.1 V for certain chemistries. An internal amplifier buffers the
ADJ pin and adjusts the internal reference voltage on the input
to GM3. Figure 5 shows a graph of the percent change in final
battery voltage vs. the ADJ voltage. The linear portion between
0.6 V
REF
and 1.4 V
REF
follows the formula below:
V
V
V
V
BAT
AD
REF
REF
%
( )
=
×
J
4
100
The factor of four in the denominator is due to internal scaling.
When V
ADJ
is above 2.5 V, an internal comparator switches off
the ADJ amplifier, giving a 0% change in V
BAT
. Whenever the
ADJ function is not used it should be connected to VL.
The total range of adjustment is
±
10%. For example, the 4.2 V
final battery voltage setting can be adjusted from 3.78 V to
4.62 V. Of course, care must be taken not to adjust the final
battery voltage to an unsafe charging level for Li-Ion batteries.
Follow the battery manufacturers specifications for the appro-
priate final battery voltage. Never charge a Li-Ion battery above
the manufacturers rated maximum!
Voltage Loop Accuracy
The ADP3801/ADP3802 guarantees that the battery voltage be
within
±
0.75% of the setpoint over the specified temperature
range and the specified charge current range. This inclusive
specification saves the designer the time and expense of having
to design-in additional high accuracy components such as a
reference and precision resistors.
To maintain the
±
0.75% specification, the layout and design of
the external circuitry must be considered. The input impedance
of BATA and BATB is typically 265 k
, so any additional im-
pedance on these inputs will cause an error. As a result, do not
add external resistors to the battery inputs. Furthermore, if the
output voltage is being used for other purposes, such as to sup-
ply additional circuitry, the current to this circuitry should be
routed separately from the sense lines to prevent voltage drops
due to impedance of the PC-board traces. In general, route the
sense lines as Kelvin connections as close to the positive termi-
nals of the battery as possible.
The same care must be given to the ground connection for the
ADP3801/ADP3802. Any voltage difference between the bat-
tery ground and the GND pin will cause an error in the charge
voltage. This error includes the voltage drop due to the ground
current of the part. Thus, the GND pin should have a thick
trace or ground plane connected as close as possible to the
battery’s negative terminal. Any current from additional cir-
cuitry should be routed separately to the supply return and not
share a trace with the GND pin.
Dual Battery Operation
The ADP3801/ADP3802 is designed to charge two separate
battery packs. These batteries can be of different chemistries
and have a different number of cells. At any given time, only
one of the two batteries is being charged. To select which bat-
tery is being monitored, and therefore which battery is being
charged, the ADP3801/ADP3802 includes a battery selector
mux. This two-channel mux is designed to be “break-before-
make” to ensure that the two batteries are not shorted together
momentarily when switching from one to the other. The A/B
input is a standard logic input, with a logic low selecting BATA
and a logic high selecting BATB. See the application in Figure
31 for more information.
Overvoltage Comparator
GM3 includes an overvoltage comparator. Its output bypasses
the COMP node to quickly reduce the duty cycle of the PWM
to 0% when an overvoltage event occurs. A second output is
connected to the COMP node and, with slower response, re-
duces the voltage on the COMP cap to provide a soft start re-
covery. The threshold of the comparator is typically 8% above
the final battery voltage. This comparator protects external
circuitry from any condition that causes the output voltage to
quickly increase. The most likely reason is if the battery is
suddenly removed while it is being charged with high current.
Figure 27 shows the transient response when the battery is
removed. Notice that the output voltage increases to the com-
parator trip point, but it is quickly brought under control and
held at the final battery voltage.
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