NI-MH MODE (LP3945 ONLY)

Programming the “mode” bit to HIGH sets the LP3945 to

Ni-MH mode and charges the battery in constant voltage

mode until the battery voltage reaches 5.4V. Since each cell

of the Ni-MH is 1.25V when fully charged, the LP3945 can

only charge exactly four cells. Charging is terminated by the

system micro-controller timer by monitoring the charge cur-

rent. The system micro-controller reads the charge current

value from the Diff Amp output. Charge current in Ni MH can

be programed as in Li Ion mode, from 950 mA to 500 mA in

50 mA step. The 5.6 hr timer is disabled in Ni-MH mode.

I

I

parameters as shown in Table 3. The LP3945 operates on

default settings during power up. Once programmed, the

LP3945 retains the register data as long as the battery

voltage is above 2.85V. Table 4 shows the charge current

and EOC current programming code.

Figures 7, 8 display I

TABLE 3. LP3945 Serial Port Communication Address Code

7h'45

LP3945 Control and Data Codes

Addrs

Register

7

6

5

4

3

2

1

0

8'h00

Charger

Register −1

Mode

(0) = Li-Ion

1 = Ni-MH

Batt Voltage

(0) = 4.1V

1 = 4.2V

Charger

Current

Code 3

(0)

Charger

Current

Code 2

(0)

Charger

Current

Code 1

(0)

Charger

Current

Code 0

(0)

8'h01

Charger

Register −2

EOC

(Green LED)

R/O

Charging

(Red LED)

R/O

EOC Sel −1

(0)

EOC Sel −0

(1)

Numbers in parentheses indicate default setting. “0” bit is set to low state, and “1” bit is set to high state. R/O — Read Only. All other bits are Read and Write.

TABLE 4. Charger Current and EOC Current Programming Code

Data Code

Charger Current Selection

Code I

Data Code

End of Charge Current

Selection Code

4h'00

500

4h'01

550

2h’1

0.1C

4h'02

600

2h’2

0.15C

4h'03

650

2h’3

0.2C

4h'04

700

4h'05

750

4h'06

800

4h'07

850

4h'08

900

4h'09

950

20066517

w = write (sda = “0”)

r = read (sda = “1”)

ack = acknowledge (sda pulled down by either master or slave)

rs = repeated start

FIGURE 7. LP3945 (Slave) Register Write

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