DS1306ENSLASHTR datasheet(9/21 Pages) DALLAS

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DS1306

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Table 2. TRICKLE CHARGER RESISTOR AND DIODE SELECT

TCS

Bit 7

TCS

Bit 6

TCS

Bit 5

TCS

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

FUNCTION

Disabled

1 Diode, 2kΩ

1 Diode, 4kΩ

1 Diode, 8kΩ

2 Diodes, 2kΩ

2 Diodes, 4kΩ

2 Diodes, 8kΩ

Initial power-on state

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 5V 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 IMAX would, therefore, be calculated as follows:

IMAX = (5.0V - diode drop) / R1

» (5.0V - 0.7V) / 2kΩ » 2.2mA

As the super cap charges, the voltage drop between VCC1 and VCC2 decreases and, therefore, the charge

current decreases.

POWER CONTROL

Power is provided through the VCC1, VCC2, and VBAT pins. Three different power supply configurations

are illustrated in Figure 4. 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. When VCC falls below VBAT the device switches into a low-current battery

backup mode. Upon power-up, the device switches from VBAT to VCC when VCC is greater than

VBAT + 0.2V. The device is write-protected whenever it is switched to 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 operates from the larger of VCC1 or

VCC2. When VCC1 is greater than VCC2 + 0.2V (typical), VCC1 powers the DS1306. When VCC1 is less than

VCC2, VCC2 powers 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.

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