Datasheet

Trickle Charger (10h)
The simplified schematic in Figure3 shows the basic components of the trickle charger. The trickle-charge select bits
(TCS[3:0])controltheselectionofthetricklecharger.Topreventaccidentalenabling,onlyapatternon1010enablesthe
trickle charger. All other patterns disable the trickle charger. The trickle charger is disabled when power is first applied.
Thediode-select(DS[1:0])bitsselectwhetherornotadiodeisconnectedbetweenV
CC
andV
BACKUP
.TheROUT[1:0]
bitsselectthevalueoftheresistorconnectedbetweenV
CC
andV
BACKUP
. Table6 shows the register settings.
Warning: The ROUT value of 200Ω must not be selected whenever V
CC
is greater than 3.63V.
Theuserdeterminesdiodeandresistorselectionaccordingtothemaximumcurrentdesiredforbatteryorsupercap
charging.Themaximumchargingcurrentcanbecalculatedasillustratedinthefollowingexample.Assumethata3.3V
systempowersupplyisappliedtoV
CC
andasupercapisconnectedtoV
BACKUP
. Also assume that the trickle charger
hasbeenenabledwithadiodeandresistorR2betweenV
CC
andV
BACKUP
.ThemaximumcurrentI
MAX
would therefore
becalculatedasfollows:
I
MAX
=(3.3V-diodedrop)/R2≈(3.3V-0.7V)/2kΩ≈1.3mA
Asthesupercaporbatterycharges,thevoltagedropbetweenV
CC
andV
BACKUP
decreases and therefore the charge
current decreases.
Table 6. Trickle Charger Register (10h)
Figure 3. Trickle Charger
R1
200Ω
R2
2kΩ
R3
4kΩ
V
CC
V
BACKUP
BIT 7
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
TCS3 TCS2 TCS1 TCS0 DS1 DS0 ROUT1 ROUT0
TRICKLE-
CHARGE
REGISTER
1 0F 16 SELECT
NOTE: ONLY 1010 CODE ENABLES CHARGER
1 OF 2
SELECT
1 OF 3
SELECT
TCS[3:0] = TRICKLE-CHARGE SELECT
DS[1:0] = DIODE SELECT
ROUT[1:0] = RESISTOR SELECT
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
FUNCTION
TCS3 TCS2 TCS1 TCS0 DS1 DS0 ROUT1 ROUT0
X X X X 0 0 X X Disabled
X X X X 1 1 X X Disabled
X X X X X X 0 0 Disabled
1 0 1 0 0 1 0 1
Nodiode,200Ωresistor
1 0 1 0 1 0 0 1 Onediode,200Ωresistor
1 0 1 0 0 1 1 0 Nodiode,2kΩresistor
1 0 1 0 1 0 1 0 Onediode,2kΩresistor
1 0 1 0 0 1 1 1 Nodiode,4kΩresistor
1 0 1 0 1 0 1 1 Onediode,4kΩresistor
0 0 0 0 0 0 0 0 Initial power-up values
DS1339B Low-Current, I
2
C, Serial Real-Time Clock
For High-ESR Crystals
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