DS1306 datasheet(8/20 Pages) DALLAS

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DS1306

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TRICKLE CHARGER RESISTOR SELECT Table 2

RS BITS

RESISTOR

TYPICAL VALUE

None

2 k

Ω

4 k

Ω

8 k

Ω

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 VCC1 and a super cap is

connected to VCC2. Also assume that the trickle charger has been enabled with one diode and resister R1

between VCC1 and VCC2. The maximum current I MAX would therefore be calculated as follows:

IMAX

= (5.0V - diode drop)/R1

~ (5.0V - 0.7V)/2 k

Ω

~ 2.2 mA

Obviously, as the super cap charges, the voltage drop between VCC1 and VCC2 will decrease and therefore

the charge current will decrease.

POWER CONTROL

Power is provided through the VCC1, VCC2, and VBAT 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

VCC1 and VCC2 is grounded. The DS1306 will be write-protected if VCC1 is less than VBAT.

Configuration 2 illustrates the DS1306 being backed up by a rechargeable energy source. In this case, the

VBAT pin is grounded, VCC1 is connected to the primary power supply, and VCC2 is connected to the

secondary supply (the rechargeable energy source). The DS1306 will operate from the larger of VCC1 or

VCC2. When VCC1 is greater than VCC2 + 0.2 volt (typical), VCC1 will power the DS1306. When VCC1 is

less than VCC2, VCC2 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 VCC1 and VBAT pins are grounded and the battery is connected to the VCC2 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 VCC, 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 VCC.

DS1306 Datasheet(PDF) 8 Page - Dallas Semiconductor

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