DS1339 Datasheet, PDF (14/18 Pages) Dallas Semiconductor – Serial Real-Time Clock

DS1339 I²C Serial Real-Time Clock
TRICKLE CHARGER REGISTER (10h)
The simplified schematic in Figure 7 shows the basic components of the trickle charger. The trickle-charge select
(TCS) bits (bits 4 to 7) 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) bits (bits 2 and 3) select whether or not a diode is connected between
V_CC and V_BACKUP. The ROUT bits (bits 0 and 1) select the value of the resistor connected between V_CC and V_BACKUP.
Table 3 shows the bit values.
Table 3. Trickle Charger Register (10h)
BIT 7
TCS3
X
X
X
1
1
1
1
1
1
0
BIT 6
TCS2
X
X
X
0
0
0
0
0
0
0
BIT 5
TCS1
X
X
X
1
1
1
1
1
1
0
BIT 4
TCS0
X
X
X
0
0
0
0
0
0
0
BIT 3
DS1
0
1
X
0
1
0
1
0
1
0
BIT 2
DS0
0
1
X
1
0
1
0
1
0
0
BIT 1
ROUT1
X
X
0
0
0
1
1
1
1
0
BIT 0
ROUT0
X
X
0
1
1
0
0
1
1
0
FUNCTION
Disabled
Disabled
Disabled
No diode, 250W resistor
One diode, 250W resistor
No diode, 2kW resistor
One diode, 2kW resistor
No diode, 4kW resistor
One diode, 4kW resistor
Initial power-up values
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) / 2kW » 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.
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