ds1305et-r Maxim Integrated Products, Inc., ds1305et-r Datasheet - Page 9

• Manufacturer Part Number: ds1305et-r
• Description: Ds1305 Serial Alarm Real-time Clock
• Manufacturer: Maxim Integrated Products, Inc.

Table 2. TRICKLE CHARGER RESISTOR AND DIODE SELECT
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 system power supply of 5V is applied to V
V
and V
As the super cap charges, the voltage drop between V
current decreases.
POWER CONTROL
Power is provided through the V
are illustrated in Figure 4. Configuration 1 shows the DS1305 being backed up by a nonrechargeable
energy source such as a lithium battery. In this configuration, the system power supply is connected to
V
accessible when V
Configuration 2 illustrates the DS1305 being backed up by a rechargeable energy source. In this case, the
V
secondary supply (the rechargeable energy source). The DS1305 operates from the larger of V
V
V
Configuration 3 shows the DS1305 in battery operate mode where the device is powered only by a single
battery. In this case, the V
Only these three configurations are allowed. Unused supply pins must be grounded.
Bit 7
CC2
CC1
BAT
CC2
CC2
TCS
X
X
X
1
1
1
1
1
1
0
. Also assume that the trickle charger has been enabled with 1 diode and resister R1 between V
. When V
, V
and V
CC2
pin is grounded, V
CC2
. The maximum current I
Bit 6
TCS
X
X
X
0
0
0
0
0
0
1
CC2
powers the DS1305. The DS1305 does not write-protect itself in this configuration.
CC1
is grounded. The DS1305 is write-protected if V
Bit 5
TCS
is greater than V
CC1
I
X
X
X
1
1
1
1
1
1
0
MAX
is greater than V
= (5.0V - diode drop) / R1 » (5.0V - 0.7V) / 2kW » 2.2mA
Bit 4
TCS
CC1
CC1
X
X
X
0
0
0
0
0
0
1
and V
is connected to the primary power supply, and V
Bit 3
DS
CC1
MAX
X
0
1
0
0
0
1
1
1
1
CC2
BAT
, V
would, therefore, be calculated as follows:
BAT
+ 0.2V (typical), V
pins are grounded and the battery is connected to the V
CC2
Bit 2
DS
X
0
1
1
1
1
0
0
0
1
+ 0.2V.
, and V
Bit 1
RS
X
X
0
0
1
1
0
1
1
0
9 of 21
BAT
Bit 0
pins. Three different power-supply configurations
CC1
RS
X
X
0
1
0
1
1
0
1
0
CC1
and V
powers the DS1305. When V
CC1
Initial power-on state
CC2
FUNCTION
2 Diodes, 2kΩ
2 Diodes, 4kΩ
2 Diodes, 8kΩ
is less than V
1 Diode, 2kΩ
1 Diode, 4kΩ
1 Diode, 8kΩ
decreases and, therefore, the charge
Disabled
Disabled
Disabled
CC1
and a super cap is connected to
BAT
CC2
. The DS1305 is fully
is connected to the
CC1
CC2
is less than
pin.
CC1
CC1
or