Rainbow-electronics DS1672 Instrukcja Użytkownika Pobierz pdf (Strona 8)

DS1672

8 of 12

Data Retention Mode

The device is fully accessible and data can be written and ready only when V

is greater than V

However, when V

falls below V

, (point at which write protection occurs) the internal clock registers

are blocked from any access. If V

is less than V

BACKUP

, the device power is switched from V

BACKUP

when V

drops below V

. If V

is greater than V

BACKUP

, the device power is switched from

to V

BACKUP

when V

drops below V

BACKUP

. The registers are maintained from the V

BACKUP

source

until V

is returned to nominal levels.

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 (I

BACKUP

) when in back-up mode. When the DS1672 is

CC,

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.

Microprocessor Monitor

A temperature-compensated comparator circuit monitors the level of V

. When V

falls to the power-

fail trip point, the RST signal (open drain) is pulled active. When V

returns to nominal levels, the RST

signal is kept in the active state for 250ms (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 250ms plus the startup time of the oscillator.

Trickle Charger

The trickle charger is controlled by the trickle charge register. The simplified schematic of Figure 5

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 V

and V

BACKUP

. 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 V

and V

BACKUP

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 TCS TCS TCS DS DS RS RS FUNCTION

XXXX 0 0XXDisabled

XXXX 1 1XXDisabled

XXXXXX 0 0Disabled

10100101

No diode, 250W resistor

10101001

One diode, 250W resistor

10100110

No diode, 2kW resistor

10101010

One diode, 2kW resistor

10100111

No diode, 4kW resistor

10101011

One diode, 4kW resistor

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

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