SC813 datasheet(13/23 Pages) SEMTECH

13 / 23 page

SC811 / SC813

Applications Information (continued)

the resistance between IPRGM and GND according to the

equation

When either of the USB modes is selected, the pro-

grammed CC regulation fast-charge current is inversely

proportional to the resistance between IPUSB and GND

according to the equation

The fast-charge current can be programmed for a

minimum of 70mA and a maximum of 995mA for either

adapter or USB high power mode. This range for both

modes permits the use of USB high power mode for

general purpose adapter charging, allowing fully inde-

pendent programming of termination current. (See the

application sections, Independent Programming of

Termination Current, and USB-only Charging of Very

Large Batteries.)

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

or R

IPUSB

(for adapter

or USB high power mode, respectively) is shown in Figures

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

current versus nominal R

IPRGM

or R

IPUSB

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 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 addressed

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),

typically 2.8V. Pre-charge current conditions the battery

for fast charging. The pre-charge current value is fixed at

20% nominally of the fast-charge current. It is pro-

grammed by the resistance between IPRGM and GND for

adapter mode and USB high power mode, and by the

resistance between IPUSB and GND for USB low power

mode. Note that USB low power mode pre-charge current

is equal to USB low power mode fast-charge current.

22.5

33.5

44.5

55.5

66.5

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

IPRGM

or R

IPUSB

(kΩ), R-tol = 1%

Figure 1a — Fast-charge Current Tolerance versus

Programming Resistance, Low Resistance Range

11121314

15161718

19202122

232425

26272829

100

125

150

175

200

225

250

275

300

325

IPRGM

or R

IPUSB

(kΩ), R-tol = 1%

Figure 1b — Fast-charge Current Tolerance versus

Programming Resistance, High Resistance Range

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