MX881

6

7/30/07

Drawing No. 088109

www.claremicronix.com

MX881

IXYS

Average Battery Current

The 3 bits (ABC2 – ABC0) of the control register are used to program the maximum average battery

current during a charge cycle. The MX881 does this by limiting the minimum off time during a switching

cycle. The off time compensates for variation of the battery voltage so that the average current is

independent of battery voltage. The default value of ABC is 101. With the default value of ABC, the

average battery current control circuits are disabled for maximum efficiency, and the maximum battery

current is approximately 220mA. The average current versus the output voltage is shown in Figure1.

The battery current peak value is preset internally to 0.7A. This current must be averaged by placing an

external bypass capacitor from VCC to ground. A 10uF capacitor is recommended for good current

smoothing and averaging.

Figure 1 - Average Battery Current

Average Battery Current Setting of 50mA (ABC = 000)

0

10

20

30

40

50

60

0

100

200

300

400

V

VCC = 3.0V

VCC = 5.5V