Table 2. trickle charger resistor and diode select, Power control – Rainbow Electronics DS1305 User Manual
Page 9
DS1305
9 of 20
Table 2. TRICKLE CHARGER RESISTOR AND DIODE SELECT
TCS
Bit 7
TCS
Bit 6
TCS
Bit 5
TCS
Bit 4
DS
Bit 3
DS
Bit 2
RS
Bit 1
RS
Bit 0
FUNCTION
X
X
X
X
X
X
0
0
Disabled
X
X
X
X
0
0
X
X
Disabled
X
X
X
X
1
1
X
X
Disabled
1
0
1
0
0
1
0
1
1 Diode, 2kΩ
1
0
1
0
0
1
1
0
1 Diode, 4kΩ
1
0
1
0
0
1
1
1
1 Diode, 8kΩ
1
0
1
0
1
0
0
1
2 Diodes, 2kΩ
1
0
1
0
1
0
1
0
2 Diodes, 4kΩ
1
0
1
0
1
0
1
1
2 Diodes, 8kΩ
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
CC1
and a super cap is connected to
V
CC2
. Also assume that the trickle charger has been enabled with 1 diode and resister R1 between V
CC1
and V
CC2
. The maximum current I
MAX
would, therefore, be calculated as follows:
I
MAX
= (5.0V - diode drop) / R1
» (5.0V - 0.7V) / 2kW » 2.2mA
As the super cap charges, the voltage drop between V
CC1
and V
CC2
decreases and, therefore, the charge
current decreases.
POWER CONTROL
Power is provided through the V
CC1
, V
CC2
, and V
BAT
pins. Three different power-supply configurations
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
CC1
and V
CC2
is grounded. The DS1305 is write-protected if V
CC1
is less than V
BAT
. The DS1305 is fully
accessible when V
CC1
is greater than V
BAT
+ 0.2V.
Configuration 2 illustrates the DS1305 being backed up by a rechargeable energy source. In this case, the
V
BAT
pin is grounded, V
CC1
is connected to the primary power supply, and V
CC2
is connected to the
secondary supply (the rechargeable energy source). The DS1305 operates from the larger of V
CC1
or
V
CC2
. When V
CC1
is greater than V
CC2
+ 0.2V (typical), V
CC1
powers the DS1305. When V
CC1
is less than
V
CC2
, V
CC2
powers the DS1305. The DS1305 does not write-protect itself in this configuration.
Configuration 3 shows the DS1305 in battery operate mode where the device is powered only by a single
battery. In this case, the V
CC1
and V
BAT
pins are grounded and the battery is connected to the V
CC2
pin.
Only these three configurations are allowed. Unused supply pins must be grounded.