Protection Features

Overvoltage Detection

If any cell voltage exceeds the overvoltage threshold,

the MAX1906 stops sampling and monitors the cell volt-

age continuously. If the overvoltage condition persists

for more than 2.1s, the device turns on an internal SCR

and also drives the DRV pin high. The internal SCR or

the external MOSFET sinks sufficient current to blow the

three-terminal protection fuse and permanently open

the battery pack’s charge path. See the overvoltage

protection flowchart in Figure 8. Also see the Fuse

Drive Options section for discussion on current capabil-

ity for both the internal SCR and external MOSFET.

The MAX1906 remains in overvoltage mode until the

cell voltage drops to 90% of the overvoltage threshold

threshold. The DRV pin then goes low, which turns off

an external MOSFET. The internal SCR does not

unlatch until power is removed.

Disconnected Pin Detection

The MAX1906 tests for disconnected voltage sense pins

each time it exits the standby or test mode. To check for

a disconnection, the MAX1906 applies a 10µA current

source to each B_P pin. A disconnected pin is detected

if the B_P pin under test falls to within 1.2V of the cell’s

negative terminal. The DISCON pin is then pulled low.

This condition persists while the MAX1906 is in normal

operating mode, and resets only when the MAX1906

enters the standby or test mode. See Figure 9 for the

disconnected pin detection flowchart.

Li+ Battery-Pack Protector with

Integrated Fuse Driver

10

______________________________________________________________________________________

STOP SAMPLING

AND START 2.1s

TIMER AND MONITOR

CELL CONTINUOUSLY

DRV = H

SCR LATCHED

WAIT

2.56s

DRV = L

SAMPLE B_P

SAMPLE MODE

AND TIMER = 2.1s?

ALL CELLS CHECKED?

YES

YES

YES

YES

NO

NO

NO

NO

DISCON = H

DISCON = L

CHECK DISCONNECTION

OF B_P PIN

SAMPLE MODE

EXIT FROM STANDBY MODE OR TEST MODE

ALL PINS CHECKED?

IS B_P AT LEAST 1.2V ABOVE

NEGATIVE TERMINAL

YES

YES

NO

NO

Figure 8. Overvoltage Protection

Figure 9. Disconnected Pin Description