DS1672U-3 datasheet(3/13 Pages) DALLAS

3 / 13 page

DS1672

3 of 13

OSCILLATOR CONTROL

The EOSC bit (bit 7 of the control register) controls the oscillator when in back-up mode. This bit when

set to logic 0 will start the oscillator. When this bit is set to a logic 1, the oscillator is stopped and the

DS1672 is placed into a low-power standby mode with a current drain of less than 200 nanoamps when in

back-up mode. When the DS1672 is powered by VCC, the oscillator is always on regardless of the status

of the EOSC bit; however, the counter is incremented only when EOSC is a logic 0.

CRYSTAL SELECTION

A standard 32.768 kHz quartz crystal should be directly connected to the X1 and X2 oscillator pins. The

crystal selected for use should have a specified load capacitance (CL) of 6 pF. For more information on

crystal selection and crystal layout considerations, please consult Application Note 58, “Crystal

Considerations with Dallas Real Time Clocks.”

MICROPROCESSOR MONITOR

A temperature-compensated comparator circuit monitors the level of VCC. When VCC falls to the power-

fail trip point, the RST signal (open drain) is pulled active. When VCC returns to nominal levels, the RST

signal is kept in the active state for 250 ms (typically) to allow the power supply and microprocessor to

stabilize. Note, however, that if the EOSC bit is set to a logic 1 (to disable the oscillator during write

protection), the reset signal will be kept in an active state for 250 ms plus the start-up time of the

oscillator.

TRICKLE CHARGER

The trickle charger is controlled by the trickle charge register. The simplified schematic of Figure 3

shows the basic components of the trickle charger. The trickle charge select (TCS) bit (bits 4-7) controls

the selection of the trickle charger. In order to prevent accidental enabling, only a pattern on 1010 will

enable the trickle charger. All other patterns will disable the trickle charger. The DS1672 powers up

with the trickle charger disabled. The diode select (DS) bits (bits 2-3) select whether or not a diode is

connected between VCC and VBACKUP. If DS is 01, no diode is selected or if DS is 10, a diode is selected.

The RS bits (bits 0-1) select whether a resistor is connected between VCC and VBACKUP and what the value

of the resistor is. The resistor selected by the resistor select (RS) bits and the diode selected by the diode

select (DS) bits are as follows:

TCS

Function

XXX

XXDisabled

XXX

XXDisabled

XXX

XX0

Disabled

010

0101

No diode, 100

Ω resistor

010

1001

One diode, 100

Ω resistor

010

0110

No diode, 2 k

Ω resistor

010

1010

One diode, 2 k

Ω resistor

010

0111

No diode, 4 k

Ω resistor

010

1011

One diode, 4 k

Ω resistor

DS1672U-3 Datasheet(PDF) 3 Page - Dallas Semiconductor

DS1672U-3 Datasheet(HTML) 3 Page - Dallas Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13

Datasheet Download

Link URL