DS1306
TRICKLE CHARGER RESISTOR SELECT
Table 2
RS BITS
00
01
10
11
RESISTOR
None
R1
R2
R3
TYPICAL VALUE
None
2 kΩ
4 kΩ
8 kΩ
If RS is 00, the trickle charger is disabled independently of TCS.
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 5 volts is applied to V
CC1
and a super cap is
connected to V
CC2
. Also assume that the trickle charger has been enabled with one 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)/2 kΩ
~ 2.2 mA
Obviously, as the super cap charges, the voltage drop between V
CC1
and V
CC2
will decrease and therefore
the charge current will decrease.
POWER CONTROL
Power is provided through the V
CC1
, V
CC2
, and V
BAT
pins. Three different power supply configurations
are illustrated in Figure 5. Configuration 1 shows the DS1306 being backed up by a non-rechargeable
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 DS1306 will be write-protected if V
CC1
is less than V
BAT
.
Configuration 2 illustrates the DS1306 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 DS1306 will operate from the larger of V
CC1
or
V
CC2
. When V
CC1
is greater than V
CC2
+ 0.2 volt (typical), V
CC1
will power the DS1306. When V
CC1
is
less than V
CC2
, V
CC2
will power the DS1306. The DS1306 does not write-protect itself in this
configuration.
Configuration 3 shows the DS1306 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.
SERIAL INTERFACE
The DS1306 offers the flexibility to choose between two serial interface modes. The DS1306 can
communicate with the SPI interface or with a standard 3-wire interface. The interface method used is
determined by the SERMODE pin. When this pin is connected to V
CC
, SPI communication is selected.
When this pin is connected to ground, standard 3-wire communication is selected.
SERIAL PERIPHERAL INTERFACE (SPI)
The serial peripheral interface (SPI) is a synchronous bus for address and data transfer and is used when
interfacing with the SPI bus on specific Motorola microcontrollers such as the 68HC05C4 and the
68HC11A8. The SPI mode of serial communication is selected by tying the SERMODE pin to V
CC
.
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DALLAS [ DALLAS SEMICONDUCTOR ]
