Detailed Description

The MAX1906 protects 2-, 3-, or 4-series Li+ battery

packs from overcharge by controlling a three-terminal

protection fuse. Figures 1 and 2 show two application

circuits using the MAX1906. The MAX1906 checks the

voltage of each cell at regular intervals. An overcharge

condition is detected if any cell voltage exceeds the

overvoltage threshold for more than 2.1s. The MAX1906

responds to an overcharge condition by turning on an

internal SCR (Figure 1) or an external MOSFET (Figure 2)

to blow a three-terminal protection fuse placed in series

with the charging path.

The MAX1906 checks for disconnected voltage sense

pins every time it exits the standby mode or test mode. If

a disconnected pin is detected, the DISCON pin is

latched low. The MAX1906 also includes a test mode,

which determines if the circuit is operating correctly while

in an assembled battery pack. A pulse on the TEST pin

enables the test mode. Figure 3 shows the cell connec-

tions for 2- and 3-series battery packs and Figure 4

shows the functional diagram for the MAX1906.

The MAX1906 can be used together with other

resettable protection circuits to provide a high level of

safety against overcharging Li+ batteries. Figure 5 shows

a typical application circuit using the MAX1906 together

with the MAX1924. The MAX1924 has a lower overvoltage

threshold than the MAX1906. If any cell voltage exceeds

4.35V (typ), the MAX1924 turns off the TKO and CGO

MOSFETs and opens the charging path. If the TKO or

CGO MOSFET fails and charging continues, the

MAX1906 blows the protection fuse and opens the charg-

ing path permanently once any cell voltage reaches

4.45V (typ). The MAX1924 also protects the battery pack

against undervoltage, charge current, discharge current,

and pack-short fault conditions. Refer to the MAX1894/

MAX1924 data sheets for complete details.

Li+ Battery-Pack Protector with

Integrated Fuse Driver

_______________________________________________________________________________________

5

Pin Description

PIN

MAX1906S

MAX1906V

MAX1906X

NAME

DESCRIPTION

1, 9

1, 9

1, 9

I.C.

Internal Connection. Float pins 1 and 9.

6, 11, 13, 15

6, 11, 13, 15

6, 11, 13, 15

N.C.

No Connection

2

2

2

DRV

MOSFET Driver Output. High when an overvoltage condition is detected.

Connect the DRV pin to the gate of an external MOSFET to blow the

protection fuse.

3

3

3

TEST

Test-Mode Input. Test mode is enabled with a pulse of minimum 50µs

duration on the TEST pin.

4

4

4

DISCON

Disconnected Pin Output. This is an open-drain output and is high-Z during

normal operation. If B4P, B3P, B2P, or B1P is disconnected, this pin is

pulled low (see the Disconnected Pin Detection section).

5

5

5

PKN

Pack Negative. A sense resistor may be connected between BN and PKN.

7

7

7

OUT

Anode Output of the SCR. Connect OUT to the fuse’s heater connection (see

the Protection Fuse Selection section).

88

8

BN

Negative Terminal of Cell 1. Connect BN to the negative terminal of the first

series Li+ cell. BN is also chip ground, which is connected to the backside

paddle on the QFN package.

10

10

10

B1P

Positive Terminal of Cell 1. Connect B1P to the positive terminal of the first

series Li+ cell.

12

12

12

B2P

Positive Terminal of Cell 2. Connect B2P to the positive terminal of the

second series Li+ cell.

—

14

14

B3P

Positive Terminal of Cell 3. Connect B3P to the positive terminal of the third

series Li+ cell.

——

16

B4P

Positive Terminal of Cell 4. Connect B4P to the positive terminal of the fourth

series Li+ cell.