DS1672 Maxim, DS1672 Datasheet - Page 10

• Manufacturer Part Number: DS1672
• Description: The DS1672 low-voltage serial timekeeping chip incorporates a 32-bit counter and power-monitoring functions
• Manufacturer: Maxim

Trickle Charger
The trickle charger is controlled by the trickle charge register. The simplified schematic of Figure 5
shows the basic components of the trickle charger. The trickle charge select (TCS) bit (bits 4–7) controls
the selection of the trickle charger. In order to prevent accidental enabling, only a pattern on 1010 will
enable the trickle charger. All other patterns will disable the trickle charger. The DS1672 powers up with
the trickle charger disabled. The diode select (DS) bits (bits 2, 3) select whether or not a diode is
connected between V
The RS bits (bits 0, 1) select whether a resistor is connected between V
of the resistor is. The resistor selected by the resistor select (RS) bits and the diode selected by the diode
select (DS) bits are as follows:
Warning: The resistor value of 250Ω must not be selected whenever V
than 3.63V.
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 3V is applied to V
connected to V
between V
As the super cap changes, the voltage drop between V
charge current will decrease.
TCS
X
X
X
1
1
1
1
1
1
0
TCS
X
X
X
0
0
0
0
0
0
0
CC
and V
BACKUP
TCS
X
X
X
1
1
1
1
1
1
0
BACKUP
I
CC
MAX
. Also assume that the trickle charger has been enabled with a diode and resistor R2
TCS
and V
X
X
X
0
0
0
0
0
0
0
= (5.0V - diode drop) / R1 ≈ (5.0V - 0.6V) / 2kΩ ≈ 2.2mA
. The maximum current I
BACKUP
DS
X
0
1
0
1
0
1
0
1
0
. If DS is 01, no diode is selected or if DS is 10, a diode is selected.
DS
X
0
1
1
0
1
0
1
0
0
RS
X
X
0
0
0
1
1
1
1
0
10 of 15
MAX
CC
RS
X
X
would, therefore, be calculated as follows:
0
1
1
0
0
1
1
0
and V
Disabled
Disabled
Disabled
No diode, 250Ω resistor
One diode, 250Ω resistor
No diode, 2kΩ resistor
One diode, 2kΩ resistor
No diode, 4kΩ resistor
One diode, 4kΩ resistor
Initial default value--disabled
BACKUP
will decrease and, therefore, the
CC
FUNCTION
and V
CC
BACKUP
and a super cap is
CC
and what the value
is greater
DS1672