DS1672 Datasheet, PDF (4/13 Pages) Dallas Semiconductor – Low Voltage Serial Timekeeping Chip

DS1672
Diode and resistor selection is determined by the user 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 system power supply of 3 volt 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 = (3.0V – diode drop) / R2
~ (3.0V – 0.7V) / 2 kΩ
~ 1.2 mA
Obviously, as the super cap changes, the voltage drop between V_CC and V_BACKUP will decrease and
therefore the charge current will decrease.
DS1672 PROGRAMMABLE TRICKLE CHARGER Figure 3
V_CC
R1
100^Ω
R2
2k^Ω
Ω
R3
4k^Ω
V_BACKUP
1 OF 16 SELECT
NOTE: ONLY 1010 ENABLES
1 OF 2
SELECT
1 OF 3
SELECT
TCS TCS TCS TCS DS
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3
DS
BIT 2
TRICKLE CHARGE REGISTER
RS
BIT 1
RS
BIT 0
TCS = TRICKLE CHARGER SELECT
DS = DIODE SELECT
RS = RESISTOR SELECT
4 of 13