MAX1665S Datasheet, PDF (8/12 Pages) Maxim Integrated Products – Lithium-Ion Battery Pack Protector

Lithium-Ion Battery Pack Protector
BP4
+
I₄
V₄
BP3
+
I_{3 I3P}
I_CB
V₄
R
B3P1
V₃
I_CB
V₄
R
BP2
+
I_{2 I2P}
V₂
BP1
B2P1
I_CB
V₄
R
+
V₂ R
+
V₃ R
+
V₄ R
B1P1
I_1P +
I₁
+
V₁ R
V₁
V₁
V₂
V₃
V₄
R
R
R
R
Figure 2. Sampling Mode Equivalent Circuit
Applications Information
Choosing an External MOSFET
The external N-channel MOSFETs act as gated switch-
es to enable or disable the charging/discharging
process. CHG and DSG control the gate of these exter-
nal MOSFETs to prevent damage to the Li+ cells. For
overcurrent conditions, the voltage at DSG equals the
voltage at BN, thereby reducing all current flow, includ-
ing the path through the body diode of the
N-channel MOSFET. Note that the MAX1665X clamps
the V_GS voltage to a maximum of 20V.
The IRF7101 is a low-cost, dual N-channel MOSFET
that is available in a small 8-pin SO package.
Depending on the maximum charge and discharge
rates, use different MOSFETs to optimize each applica-
tion. Table 3 summarizes recommended MOSFETs.
2, 3, and 4-Cell Applications
Figures 3 through 5 depict circuits for 2, 3, and 4-cell
applications. Note that the two series MOSFETs (IRF7101
dual N-channel MOSFETs) are oriented to prevent body
diode current flow. The indicated polarity symbols show
the connection for the external source required to charge
the Li+ cells. This external charger source also supplies
the gate drive to the MOSFETs through pack + voltage /
pack.
Table 3. Recommended MOSFETs
DUAL N-CHANNEL
MOSFETs
IRF9956
FDS6990A
Si9936
TYPICAL
R_DS(ON) (Ω)
0.10
0.018
0.050
MAX V_GS
(V)
±20
±20
±20
PACK+
CELL 2
CELL 1
OVERDISCHARGE
PROTECTION
OVERCHARGE
PROTECTION
1
I.C.
8
I.C.
7
B2P
6
B1P
5 _{BN MAX1665S}
IRF7101
2
DSG
IRF7101
3
CHG
PACK-
4
PKN
Figure 3. Typical 2-Cell Operating Circuit
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