参数资料
型号: MAX1894-MAX1924
厂商: Maxim Integrated Products, Inc.
元件分类: 数字信号处理
英文描述: Fixed-Point Digital Signal Processor 288-FCBGA
中文描述: 先进的锂电池,包保护器
文件页数: 12/16页
文件大小: 308K
代理商: MAX1894-MAX1924
M
Advanced Li+ Battery-Pack Protectors
where N
S
is the number of cells in series, N
P
is number
of cells in parallel, and V
CELL
is the cell voltage.
Dissipation during pack-short current fault condition is
given by:
The R
SENSE
chosen should be able to withstand P
PS
dissipation. Verify power dissipation in normal operation
and other current fault conditions as well.
Choosing External MOSFETs
The external P-channel MOSFETs act as switches to
enable or disable charging and discharging of batteries.
Different P-channel MOSFETs may be selected depend-
ing on the charge and discharge currents anticipated.
In most applications, the requirements for fast-charge
and discharge MOSFETs are similar and the same type
of MOSFETs can be used. The trickle-charge MOSFET
can be a small-signal type to minimize cost.
The MAX1894/MAX1924 MOSFET drivers have a V
GS
clamp of -14V typical and MOSFETs with maximum V
GS
of -20V can be used. MOSFETs must have a V
DS
greater than the maximum pack voltage.
The power dissipation in the MOSFETs is given by:
The MOSFET should be chosen to withstand power dis-
sipation during normal operation and all current fault
conditions. Additional MOSFETs can be added in paral-
lel to help these requirements. Table 3 lists some suit-
able MOSFETs in a small SO-8 package.
Decoupling Considerations
The MAX1894/MAX1924 must have a reliable V
CC
bias
to function properly. A severe overload, such as a short
circuit at the pack terminals, can collapse the battery-
pack voltage below the V
CC
undervoltage lockout
threshold. The use of a diode-capacitor peak detector
on the V
CC
input ensures continued operation during
voltage transients on the battery (Figure 1). Since the
MAX1894/MAX1924 typically consume only 30μA, D1
and C6 can be small, low-cost components. A 30V
Schottky diode with a few mA current capability and a
0.1μF capacitor are sufficient.
The MAX1894/MAX1924 continuously monitor the differ-
ential voltage between the B4P and SRC inputs to
detect the application of a charger. RC filters with simi-
lar time constants must be added to both inputs to
ensure the differential voltage is not corrupted by noise.
P
I R
DSON
=
P
I
R
PS
PS
SENSE
=
×
(
)
2
I
V
N
R
R
R
R
N
N
PS
CELL
S
DSON DSO
DSON CGO
_
SENSE
CELL
S
P
=
×
+
+
+
×
_
12
______________________________________________________________________________________
Table 2. State Table
STATE
CTL STATE
SHDN
STATE
CHARGER
APPLIED
GOES INTO
SHUTDOWN MODE
TKO
CGO
DSO
L
L
L
L
L
L
L
L
L
L
Yes
No
X
Yes
No
No
Yes
No
No
No
L
H
H
H
H
H
H
H
H
H
H
H
L
L
H
Undervoltage
Overvoltage
Charge Current Fault
Discharge Current Fault
Pack Short Current
Fault
L
L
No
No
H
H
H
X
X
H
H
H
L
No
Yes
X
Yes
No
No
H
H
H
H
H
H
H
H
H
Forced Shutdown by
External μP
CTL
Deep Discharge
(V
CC
< 4.5V)
Normal Operation
L
L
Yes
No
L
H
H
L
L
X
No
L
L
L
X: Don
t care.
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