SC813 datasheet(14/23 Pages) SEMTECH

14 / 23 page

SC811 / SC813

Pre-charge current regulation accuracy is dominated by

offset error. The range of expected pre-charge output

current versus programming resistance R

IPRGM

or R

IPUSB

shown in Figures 2a and 2b. Each figure shows the

nominal pre-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 programming 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% toler-

ance resistors. The dots on each plot indicate the currents

obtained with standard value 1% tolerance resistors.

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

respectively.

Termination

When the battery voltage reaches V

CV, the SC811/3 transi-

tions from constant current regulation to constant voltage

regulation. While V

BAT

is regulated to V

, the current into

the battery decreases as the battery becomes fully

charged. When the output current drops below the termi-

nation threshold current, charging terminates. Upon

termination, the STATB pin open drain output turns off

and the charger either enters monitor state or float-

charges the battery, depending on the logical state of the

ENB input pin.

Applications Information (continued)

The termination threshold current is fixed at 10% of the

adapter mode fast-charge current, as programmed by the

resistance between IPRGM and GND, for all charging

modes. If only the USB modes will be used, the termina-

tion threshold current can be programmed independently

of the fast-charge current. (See the application sections,

Independent Programming of Termination Current, and

USB-only Charging of Very Large Batteries.)

Charger output current is the sum of the battery charge

current and the system load current. Battery charge

current changes gradually, and establishes a slowly

diminishing lower bound on the output current while

charging in CV mode. The load current into a typical

digital system is highly transient in nature. Charge cycle

termination is detected when the sum of the battery

charging current and the greatest load current occurring

within the immediate 300μs to 550μs past interval is less

than the programmed termination current. This timing

behavior permits charge cycle termination to occur

during a brief low-load-current interval, and does not

require that the longer interval average load current be

small.

Termination threshold current accuracy is dominated by

offset error. The range of expected termination current

versus programming resistance R

IPRGM

(for any charging

mode) is shown in Figures 3a and 3b. Each figure shows

22.5

33.5

44.5

55.5

66.5

100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250

260

270

IPRGM

or R

IPUSB

(kΩ), R-tol = 1%

Figure 2a — Pre-charge Current and USB Low Power

Mode Fast-charge Current Tolerance vs. Programming

Resistance, Low Resistance Range

11121314

15161718

19202122

232425

26272829

IPRGM

or R

IPUSB

(kΩ), R-tol = 1%

Figure 2b — Pre-charge Current and USB Low Power

Mode Fast-charge Current Tolerance vs. Programming

Resistance, High Resistance Range

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