Name: DS1670E
SKU: DS1670E
Price: 5.38417 USD
Availability: InStock

1 of 17 122800

FEATURES

 Provides real time clock:

− Counts seconds, minutes, hours, date of

the month, month, day of the week, and

year with leap year compensation valid up

to 2100

− Power control circuitry supports system

power-on from day/time alarm

 Microprocessor monitor:

− Halts microprocessor during power fail

− Automatically restarts microprocessor

after power failure

− Monitors pushbutton for external override

− Halts and resets an out of control

microprocessor

 NV RAM control:

− Automatic battery backup and write

protection to external SRAM

 3-channel, 8-bit analog-to-digital converter

 Simple 3-wire interface

 3.3V operation

PIN ASSIGNMENT

Package Dimension Information can be found at:

http://www.dalsemi.com/datasheets/mechdwg.html

ORDERING INFORMATION

DS1670E 20-pin TSSOP

DS1670S 20-pin SOIC

DESCRIPTION

The Portable System Controller is a circuit, which incorporates many of the functions necessary for low

power portable products integrated into one chip. The DS1670 provides a Real Time Clock, NV RAM

controller, microprocessor monitor, and a 3-channel, 8-bit analog-to-digital converter. Communication

with the DS1670 is established through a simple 3-wire interface.

The Real Time Clock (RTC) provides seconds, minutes, hours, day, date, month, and year information

with leap year compensation. The RTC also provides an alarm interrupt. This interrupt works when the

DS1670 is powered by the system power supply or when in battery backup operation so the alarm can be

used to wake up a system that is powered down.

Automatic backup and write protection of an external SRAM is provided through the V

CCO

, CEOL , and

CEOH pins. The backup energy source used to power the RTC is also used to retain RAM data in the

absence of V

through the V

CCO

pin. The chip-enable outputs to RAM ( CEOL and CEOH ) are

controlled during power transients to prevent data corruption.

AIN0

AIN1

AIN2

RST

BLE

BHE

BAT

CCO

SCLK

I/O

CEI

CEOL

CEOH

INT

GND

20-Pin TSSOP (4.4mm)

20-Pin SOIC (300 mil)

DS1670

Portable System Controlle

www.dalsemi.com

DS1670

2 of 17

The microprocessor monitor circuitry of the DS1670 provides three basic functions. First, a precision

temperature-compensated reference and comparator circuit monitors the status of V

. When an out-of-

tolerance condition occurs, an internal power-fail signal is generated which forces the reset to the active

state. When V

returns to an in-tolerance condition, the reset signals are kept in the active state for

250 ms to allow the power supply and processor to stabilize. The second microprocessor monitor

function is pushbutton reset control. The DS1670 debounces a pushbutton input and guarantees an active

reset pulse width of 250 ms. The third function is a watchdog timer. The DS1670 has an internal timer

that forces the reset signals to the active state if the strobe input is not driven low prior to watchdog

time-out.

The DS1670 also provides a 3-channel, 8-bit successive approximation analog-to-digital converter. The

converter has an internal 2.55-volt (typical) reference voltage generated by an on-board band-gap circuit.

The A/D converter is monotonic (no missing codes) and has an internal analog filter to reduce high

frequency noise.

OPERATION

The block diagram in Figure 1 shows the main elements of the DS1670. The following paragraphs

describe the function of each pin.

DS1670 BLOCK DIAGRAM Figure 1

SIGNAL DESCRIPTIONS

, GND - DC power is provided to the device on these pins. V

is the +3.3 volt input. When

3.3 volts are applied within nominal limits, the device is fully accessible and data can be written and read.

When V

drops below 2.88 volts (typical) access to the device is prohibited. When V

drops below the

lower of V

BAT

and 2.7 volts (typical), the device is switched over to the backup power supply.

BAT

(Backup Power Supply) - Battery input for standard 3-volt lithium cell or other energy source.

SCLK (Serial Clock Input) - SCLK is used to synchronize data movement on the serial interface.

I/O (Data Input/Output) - The I/O pin is the bi-directional data pin for the 3-wire interface.

DS1670

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CS (Chip Select) - The Chip Select signal must be asserted high during a read or a write for

communication over the 3-wire serial interface. CS had an internal 40k ohm pull down resistor.

CCO

(External SRAM Power Supply Output) - This pin is internally connected to V

when V

within nominal limits. However, during power fail V

CCO

is internally connected to the V

BAT

pin.

Switchover occurs when V

drops below the lower of V

BAT

or 2.7 volts.

INT (Interrupt Output) - The INT pin is an active high output of the DS1670 that can be used as an

interrupt input to a microprocessor. The INT output remains high as long as the status bit causing the

interrupt is present and the corresponding interrupt-enable bit is set. The INT pin operates when the

DS1670 is powered by V

or V

BAT

CEI (RAM Chip Enable In) - CEI must be driven low to enable the external RAM.

BLE (Byte Low Enable input) - This pin when driven low activates the CEOL output if CEI is also

driven low.

BHE (Byte High Enable input) - This pin when driven low activates the CEOH output if CEI is also

driven low.

CEOL (RAM Chip Enable Out Low) - Chip enable output for low order SRAM byte.

CEOH (RAM Chip Enable Out High) - Chip enable output for high order SRAM byte.

ST (Strobe Input) - The Strobe input pin is used in conjunction with the watchdog timer. If the ST pin

is not driven low within the watchdog time period, the RST pin is driven low.

RST (Reset) - The RST pin functions as a microprocessor reset signal. This pin is driven low 1) when

is outside of nominal limits; 2) when the watchdog timer has “timed out”; 3) during the power up

reset period; and 4) in response to a pushbutton reset. The

RST pin also functions as a pushbutton reset

input. When the RST pin is driven low, the signal is debounced and timed such that a RST signal of at

least 250 ms is generated. This pin has an open drain output with an internal 47 kΩ pull-up resistor.

AIN0, AIN1, AIN2 (Analog Inputs) - These pins are the three analog inputs for the 3-channel analog-to-

digital converter.

X1, X2 - Connections for a standard 32.768 kHz quartz crystal. For greatest accuracy, the DS1670 must

be used with a crystal that has a specified load capacitance of 6 pF. There is no need for external

capacitors or resistors. Note: X1 and X2 are very high impedance nodes. It is recommended that they

and the crystal be guard-ringed with ground and that high frequency signals be kept away from the crystal

area. For more information on crystal selection and crystal layout considerations, please consult

Application Note 58, “Crystal Considerations with Dallas Real Time Clocks.”

The DS1670 will not function without a crystal.

Part #	DS1670E
Description	IC RTC SYSTEM CTRLR SER 20-TSSOP
Category	IC
Availability	In Stock
Qty	50

Qty	Price
1 - 10	$5.38417
11 - 21	$4.28287
22 - 31	$4.03813
32 - 42	$3.75261
43 +	$3.34471

DS1670E

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