SC908MLTRT 查看數據表（PDF） - Semtech Corporation

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SC908MLTRT

Power Management IC for Single-Cell Li-Ion Devices

Semtech Corporation 

SC908

Applications Information (continued)

200

180

160

140

120

100

80

60

5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15

RIPRGM (kΩ)

Figure 1b — Fast-charge Current Variation vs. IPRGM

Resistance, High Resistance Range

The figures show the nominal current versus nominal

R resistance as the center plot and two theoretical

IPRGM

limit plots indicating maximum and minimum current

versus nominal programming resistance. These plots are

derived from models of the expected worst-case contri-

bution of error sources depending on programmed

current. The current range includes the uncertainty due

to 1% tolerance resistors. The dots on each plot indicate

the currents obtained with standard value 1% tolerance

resistors. The figures show low and high resistance

ranges.

Termination Current

When the battery voltage reaches VCV, the SC908 transi-

tions from constant current mode to constant voltage

mode. As the output holds the voltage measured at the

BSEN pin constant, the current through the battery will

decrease as the battery becomes fully charged. CHRGB is

disabled when the output current drops below the pro-

grammed termination current. If the timer is enabled, the

output will continue to float-charge in CV mode until the

charge timer expires. If the timer is disabled, the output

will turn off as soon as the termination current level is

reached. The termination current is determined by

I I TERM Pr eQ

VITERM _ Typ u 130

RITERM

Termination current can be programmed from 14mA to

65mA, and must be less than I for correct operation of

FQ

the charge cycle. Pre-charge and termination current

regulation accuracy is dominated by offset error. The

range of expected pre-charge output current and termi-

nation threshold current versus programming resistance

R is shown in Figures 2a and 2b. The figures show the

ITERM

nominal pre-charge and termination current versus

nominal resistance as the center plot. Two theoretical

limit plots indicate maximum and minimum current

versus nominal programming resistance. These plots are

derived from models of the expected worst-case contri-

bution of error sources depending on programmed

current. The current range includes the uncertainty due

to 1% tolerance resistors. The dots on each plot indicate

the currents obtained with standard value 1% tolerance

resistors. The figures show low and high resistance

ranges.

A sufficient separation between I and I must be

FQ

TERM

maintained to ensure proper operation of the constant

current regulator and charge termination detector. R

IPRGM

and R must be chosen to nominally satisfy

ITERM

I > I + 90mA

FQ TERM

75

70

65

60

55

50

45

40

35

30

25

20

3

3.5

4

4.5

5

5.5

6

6.5

RITERM (kΩ)

Figure 2a — Pre-charge and Termination Current

Variation vs. ITERM Resistance, Low Resistance Range

16

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