SC820 datasheet(13/22 Pages) SEMTECH

13 / 22 page

SC820

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.

Pre-charge Mode

This mode is automatically enabled when the battery

voltage is below the pre-charge threshold voltage (VT

PreQ),

typically 2.9V. Pre-charge current conditions the battery

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

20% nominally of the fast-charge current for the selected

input. The fast-charge current is programmed by the

resistance between IPRGM and GND for the VAD input,

and by the resistance between IPUSB and GND for the

VUSB input.

Pre-charge current regulation accuracy is dominated by

offset error. The range of expected pre-charge output

current versus programming resistance is shown in Figures

2a and 2b. The figures show the nominal pre-charge

current versus nominal 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

Applications Information (continued)

value 1% tolerance resistors. Figures 2a and 2b show low

and high resistance ranges, respectively.

Termination

When the battery voltage reaches V

, the SC820 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

termination 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.

The termination threshold current is fixed at 10% of the

VAD input fast-charge current, as programmed by the

resistance between IPRGM and GND. The IPRGM pin

resistance determines the termination threshold current

regardless of whether the selected charging input is VAD

or VUSB.

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

Figure 2a — Pre-charge Current Tolerance versus

Programming Resistance, Low Resistance Range

2.5

3.5

4.5

5.5

6.5

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 2b — Pre-charge Current Tolerance versus

Programming Resistance, High Resistance Range

11121314

15161718

19202122

232425

26272829

IPRGM

or R

IPUSB

(kΩ), R-tol = 1%

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