SC824ULTRT Semtech, SC824ULTRT Datasheet - Page 14

• Manufacturer Part Number: SC824ULTRT
• Description: Single-cell Li-Ion Charger Tri-Mode With Timer And NTC
• Manufacturer: Semtech

Applications Information (continued)
Termination
When the battery voltage reaches V
tions from constant current regulation to constant voltage
regulation. The current into the battery decreases while
the BAT voltage is regulated to V
fully charged. When the output current drops below the
termination current threshold, charging terminates. Upon
termination, the charger either enters monitor state or
fl oat charges the battery for the top-off timer duration,
depending on the confi guration of the charge timer. After
a 20 second delay following termination, the STAT1 pin
open drain output turns off .
The termination current threshold is fi xed at 10% of the
fast-charge current, as programmed by the IPRGM pin
resistance to ground, for all charging modes.
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 dimin-
ishing lower bound on the output current while charging
in CV regulation. The load current into a typical digital
system is highly transient in nature. Charge cycle termina-
tion 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
Mode Fast-charge Current Tolerance vs. Programming
Figure 2a — Pre-charge Current and USB Low Power
270
260
250
240
230
220
210
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
2
2.5
Resistance, Low Resistance Range
3
3.5
R
IPRGM
4
(k Ω ), R-tol = 1%
4.5
CV
as the battery becomes
5
CV
, the SC824 transi-
5.5
6
© 2008 Semtech Corporation
6.5
7
low-load-current interval, and does not require that the
longer interval average load current be small.
Termination current threshold accuracy is dominated by
off set error. The range of expected termination current
versus programming resistance R
mode) is shown in Figures 3a and 3b. Each fi gure shows
the nominal termination current versus nominal R
resistance as the center plot and two theoretical limit
plots indicating maximum and minimum current vs.
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 a 1% toler-
ance resistor. The dots on each plot indicate the currents
obtained with EIA E96 standard value 1% tolerance resis-
tors. Figures 3a and 3b show low and high resistance
ranges, respectively.
Monitoring Output Current
The output current I
IPRGM pin according to the following equation.
Ensure that the IPRGM pin is not loaded or corrupted by
the processor Analog to Digital Converter (ADC). An RC
Mode Fast-charge Current Tolerance vs. Programming
Figure 2b — Pre-charge Current and USB Low Power
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
I
5
0
BAT
7
8
9
R
V
Resistance, High Resistance Range
IPRGM
IPRGM
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
1000
BAT
R
is indicated by the voltage at the
IPRGM
(k Ω ), R-tol = 1%
IPRGM
(for any charging
SC824
IPRGM
14