MAX1666A Datasheet, PDF (11/17 Pages) Maxim Integrated Products – Advanced Lithium-Ion Battery-Pack Protector

Advanced Lithium-Ion
Battery-Pack Protector
REF
MAX1666
R1
OVA
UVA
MMA
R3 R5
R2
GND
R4 R6
Figure 3. Using an External Resistor-Divider to Adjust
Overvoltage Threshold
Detailed Description
The MAX1666 battery-pack protectors supervise the
charging and discharging processes of Li+ battery
cells. Designed for 2-, 3-, and 4-cell applications, these
devices monitor the voltage across each cell to provide
protection against undervoltage, overvoltage, and over-
current damage.
Control pins CGO, TKO, and DSO allow control of
external MOSFET gates. This allows fast charging, trick-
le charging, and discharging processes (see the
Typical Operating Circuits). The voltage of each cell is
measured individually. Also, each cell is measured dif-
ferentially between every other cell of the pack.
The MAX1666 contains a state machine, a voltage reg-
ulator, an oscillator, and other logic functions to selec-
tively drive CGO, UVO, TKO, DSO, WRN, and PKF
(Figure 1).
Modes of Operation
Shutdown Mode
The MAX1666 goes into shutdown mode when a bat-
tery pack is first connected. The quiescent current is
less than 1µA. All circuitry is inactive except the com-
parator monitoring V_SRC and the top-cell voltage. The
MAX1666 remains in shutdown mode as long as V_SRC
is less than the top-cell voltage. When SRC is connect-
ed to an external charger and V_SRC is 1V above the
top-cell voltage, the device goes into standby mode.
The MAX1666 returns to shutdown mode under two
conditions: the battery is disconnected and then re-
connected, or the device detects an undervoltage fault
and no charge source.
Normal Mode
The standby state activates the bias circuitry, overcurrent
comparator, and timer. The standby state lasts 80ms,
then the MAX1666 goes into the sample state for 2.5ms.
Within the 2.5ms, the MAX1666 checks for overvoltage,
undervoltage, and mismatch between cells sequential-
ly, and it stores the results in internal latches. The
MAX1666 drives the outputs according to the faults (if
any) detected by reading the latches (Figure 2) at the
end of the sample state. Then the MAX1666 returns to
the standby state.
Overvoltage Protection
The MAX1666 provides overvoltage protection to avoid
overcharging of any cell. When any cell is at overvolt-
age, CGO and TKO go high, turning off the external
MOSFETs and stopping the charging process (see the
Typical Operating Circuits). WRN goes low. Overvoltage
is set when any cell voltage exceeds the overvoltage
threshold.
Overvoltage threshold is linearly adjustable through an
external 1% resistor-divider (Figure 3) from REF.
Determine the overvoltage threshold (V_OVT) required.
V_OVT must be between 4V and 4.4V. Set R_TOTAL = R1
+ R2 = 1MΩ. Calculate R1 and R2 as follows:
R2 = [(V_OVT - 4V) / (4.4V- 4V)] · R_TOTAL
R1 = R_TOTAL - R2
Table 1. Operating Modes
MODE
STATE
TIME
(ms)
TYPICAL
QUIESCENT
CURRENT (µA)
CONDITION
Normal
Standby
80
Sample
2.5
24
Only bias circuitry, overcurrent comparator, and timer are active.
250
All circuitry active.
Shutdown
—
—
0.7
All circuitry inactive. Device enters shutdown when it detects an undervolt-
age fault and V_SRC < V_TOP-CELL + 1V (no charge source).
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