SC824 datasheet(13/29 Pages) SEMTECH

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SC824

Applications Information (continued)

1000

IPRGM

Typ

IPRGM

The nominal fast charge current can be programmed to

any value between 70mA and 1000mA.

Current regulation accuracy is dominated by gain error at

high current settings, and offset error at low current set-

tings. The range of expected fast-charge output current

versus programming resistance R

IPRGM

is shown in Figures

1a and 1b. Each figure shows the nominal fast-charge

current versus nominal R

IPRGM

resistance as the center plot,

and two theoretical limit plots indicating maximum and

minimum current versus nominal programming resis-

tance. These plots are derived from models of the

expected worst-case contribution 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

the Electronic Industries Association (EIA) E96 standard

value 1% tolerance resistors. Figures 1a and 1b show low

and high resistance ranges, respectively. The USB low

power mode fast-charge current accuracy is exactly like

that of pre-charge in high power mode. USB low power

mode current regulation accuracy is described in the next

section.

Pre-charge and USB Low Power Mode Fast-

charge Current Regulation

Pre-charging is automatically selected when the battery

voltage is below the pre-charge threshold voltage (VT

PreQ).

Pre-charge current conditions the battery for fast charg-

ing. The pre-charge current value is fixed at 20% of the

programmed fast-charge current. Note that USB low

power mode pre-charge current is equal to USB low

power mode fast-charge current.

Pre-charge current regulation accuracy is dominated by

offset error. The range of expected pre-charge output

current versus programming resistance R

IPRGM

is shown in

Figures 2a and 2b. Each figure shows the nominal pre-

charge current versus nominal R

IPRGM

resistance as the

center plot and two theoretical limit plots indicating

maximum and minimum current versus nominal pro-

gramming resistance. These plots are derived from

models of the expected worst-case contribution of error

sources depending on programmed current. The current

range includes the uncertainty due to 1% tolerance resis-

tors. The dots on each plot indicate the currents obtained

with EIA E96 standard value 1% tolerance resistors.

Figures 2a and 2b show low and high resistance ranges,

respectively.

2.5

3.5

4.5

5.5

6.5

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

IPRGM (k

Ω), R-tol = 1%

Figure 1a — Fast-charge Current Tolerance versus

Programming Resistance, Low Resistance Range

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100

125

150

175

200

225

250

275

300

325

IPRGM (k

Ω), R-tol = 1%

Figure 1b — Fast-charge Current Tolerance versus

Programming Resistance, High Resistance Range

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