MAX1894XEEE-T Maxim Integrated, MAX1894XEEE-T Datasheet - Page 12

• Manufacturer Part Number: MAX1894XEEE-T
• Description: Battery Management
• Manufacturer: Maxim Integrated
• Series: MAX1894, MAX1924r

where N
of cells in parallel, and V
Dissipation during pack-short current fault condition is
given by:
The R
dissipation. Verify power dissipation in normal operation
and other current fault conditions as well.
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
clamp of -14V typical and MOSFETs with maximum V
of -20V can be used. MOSFETs must have a V
greater than the maximum pack voltage.
Advanced Li+ Battery-Pack Protectors
Table 2. State Table
X: Don’t care.
I
12
PS
Undervoltage
Overvoltage
Charge Current Fault
Discharge Current Fault
Pack Short Current
Fault
Forced Shutdown by
External µP
CTL
Deep Discharge
(V
Normal Operation
CC
=
______________________________________________________________________________________
R
SENSE
< 4.5V)
DSON DSO
S
STATE
is the number of cells in series, N
_
chosen should be able to withstand P
P
+
PS
Choosing External MOSFETs
R
DSON CGO
=
(
I
PS
V
CELL
CTL STATE
_
)
2
CELL
×
X
X
H
L
L
L
L
L
L
L
L
×
R
+
N
SENSE
R
S
SENSE
is the cell voltage.
+
STATE
R
SHDN
P
CELL
H
H
L
L
L
L
L
L
L
L
L
is number
×
N
N
S
P
GS
GS
DS
PS
CHARGER
APPLIED
Yes
Yes
Yes
Yes
No
No
No
No
X
X
X
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.
The MAX1894/MAX1924 must have a reliable V
to function properly. A severe overload, such as a short
circuit at the pack terminals, can collapse the battery-
pack voltage below the V
threshold. The use of a diode-capacitor peak detector
on the V
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.
CC
SHUTDOWN MODE
GOES INTO
input ensures continued operation during
Yes
Yes
No
No
No
No
No
No
No
No
No
P I R
Decoupling Considerations
=
2
DSON
CC
TKO
undervoltage lockout
L
H
H
H
H
H
H
H
H
L
L
CGO
H
H
H
H
H
H
H
H
H
H
L
CC
DSO
H
H
H
H
H
H
H
H
L
L
L
bias