DS1339A Datasheet, PDF (14/19 Pages) Maxim Integrated Products – Low-Current, I2C, Serial Real-Time Clock

DS1339A
Low-Current, I²C, Serial Real-Time Clock
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.
R1
200Ω
V_CC
R2
VBACKUP
2kΩ
R3
4kΩ
1 0F 16 SELECT
NOTE: ONLY 1010 CODE ENABLES CHARGER
TRICKLE-
CHARGE TCS3
REGISTER
BIT 7
TCS2
BIT 6
TCS1
BIT 5
TCS0
BIT 4
1 OF 2
SELECT
1 OF 3
SELECT
DS1
DS0 ROUT1 ROUT0
BIT 3
BIT 2
BIT 1
BIT 0
TCS[3:0] = TRICKLE-CHARGE SELECT
DS[1:0] = DIODE SELECT
ROUT[1:0] = RESISTOR SELECT
Figure 3. Trickle Charger
Table 6. 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, 200I resistor
One diode, 200I resistor
No diode, 2kI resistor
One diode, 2kI resistor
No diode, 4kI resistor
One diode, 4kI resistor
Initial power-up values
Warning: The ROUT value of 200I 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) / 2kI ≈ 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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