DS1340_06 datasheet(6/14 Pages) MAXIM

6 / 14 page

Detailed Description

The DS1340 is a low-power clock/calendar with a trickle

charger. Address and data are transferred serially

through a I2C bidirectional bus. The clock/calendar pro-

vides seconds, minutes, hours, day, date, month, and

year information. The date at the end of the month is

automatically adjusted for months with fewer than 31

days, including corrections for leap year. The DS1340

has a built-in power-sense circuit that detects power fail-

ures and automatically switches to the backup supply.

Power Control

The power-control function is provided by a precise,

temperature-compensated voltage reference and a

comparator circuit that monitors the VCC level. The

device is fully accessible and data can be written and

read when VCC is greater than VPF. However, when VCC

falls below VPF, the internal clock registers are blocked

from any access. If VPF is less than VBACKUP, the

device power is switched from VCC to VBACKUP when

VCC drops below VPF. If VPF is greater than VBACKUP,

the device power is switched from VCC to VBACKUP

when VCC drops below VBACKUP. The registers are

maintained from the VBACKUP source until VCC is

returned to nominal levels (Table 1). After VCC returns

above VPF, read and write access is allowed tREC.

I2C RTC with Trickle Charger

_____________________________________________________________________

Pin Description

NAME

FUNCTION

—

Connections for a Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is designed for

operation with a crystal having a specified load capacitance (CL) of 12.5pF. X1 is the input to the oscillator

and can optionally be connected to an external 32.768kHz oscillator. The output of the internal oscillator,

X2, is floated if an external oscillator is connected to X1.

VBACKUP

Connection for a Secondary Power Supply. For the 1.8V and 3V devices, VBACKUP must be held between

1.3V and 3.7V for proper operation. Diodes placed in series between the supply and the input pin may

result in improper operation. VBACKUP can be as high as 5.5V on the 3.3V device.

This pin can be connected to a primary cell such as a lithium coin cell. Additionally, this pin can be

connected to a rechargeable cell or a super cap when used with the trickle-charge feature. UL recognized

to ensure against reverse charging when used with a lithium battery (www.maxim-ic.com/qa/info/ul).

GND

Ground

SDA

Serial Data Input/Output. SDA is the data input/output for the I

2C serial interface. The SDA pin is open drain

and requires an external pullup resistor.

SCL

Serial Clock Input. SCL is the clock input for the I

2C interface and is used to synchronize data movement on

the serial interface.

FT/OUT

Frequency Test/Output. This pin is used to output either a 512Hz signal or the value of the OUT bit. When

the FT bit is logic 1, the FT/OUT pin toggles at a 512Hz rate. When the FT bit is logic 0, the FT/OUT pin

reflects the value of the OUT bit. This open-drain pin requires an external pullup resistor, and operates with

either VCC or VBACKUP applied.

VCC

Primary Power Supply. When voltage is applied within normal limits, the device is fully accessible and data

can be written and read. When a backup supply is connected to the device and VCC is below VTP, reads and

writes are inhibited. However, the timekeeping function continues unaffected by the lower input voltage.

—

4–13

N.C.

No Connection. Must be connected to ground.

SUPPLY CONDITION

READ/WRITE

ACCESS

POWERED

VCC < VPF,

VCC < VBACKUP

VBAT

VCC < VPF,

VCC > VBACKUP

VCC

VCC > VPF,

VCC < VBACKUP

Yes

VCC

VCC > VPF,

VCC > VBACKUP

Yes

VCC

Table 1. Power Control

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