MAX1924V Просмотр технического описания (PDF) - Maxim Integrated
Номер в каталоге
Компоненты Описание
производитель
MAX1924V Datasheet PDF : 16 Pages
| |||
Advanced Li+ Battery-Pack Protectors
Table 2. State Table
STATE
CTL STATE
L
Undervoltage
L
Overvoltage
L
Charge Current Fault
L
Discharge Current Fault
L
Pack Short Current
Fault
L
Forced Shutdown by
X
External µP
X
CTL
H
Deep Discharge
L
(VCC < 4.5V)
Normal Operation
L
SHDN
STATE
L
L
L
L
L
L
H
H
L
L
L
CHARGER
APPLIED
Yes
No
X
Yes
No
No
No
Yes
X
Yes
X
GOES INTO
SHUTDOWN MODE
No
Yes
No
No
No
No
Yes
No
No
No
No
TKO
L
H
H
H
H
H
H
H
H
L
L
CGO
H
H
H
H
H
H
H
H
H
H
L
DSO
H
H
L
L
H
H
H
H
H
H
L
X: Don’t care.
IPS
=
RDSON _ DSO
VCELL × NS
+ RDSON_ CGO + RSENSE
+
RCELL
×
NS
NP
where NS is the number of cells in series, NP is number
of cells in parallel, and VCELL is the cell voltage.
Dissipation during pack-short current fault condition is
given by:
PPS = (IPS )2 × RSENSE
The RSENSE chosen should be able to withstand PPS
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 VGS
clamp of -14V typical and MOSFETs with maximum VGS
of -20V can be used. MOSFETs must have a VDS
greater than the maximum pack voltage.
The power dissipation in the MOSFETs is given by:
P = I2 RDSON
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 VCC bias
to function properly. A severe overload, such as a short
circuit at the pack terminals, can collapse the battery-
pack voltage below the VCC undervoltage lockout
threshold. The use of a diode-capacitor peak detector
on the VCC 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.
12 ______________________________________________________________________________________
Share Link: 