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DS1677

Portable System Controller

Dallas Semiconductor -> Maxim Integrated 

DS1677

PIN DESCRIPTION

PIN NAME

FUNCTION

Battery Input for Standard 3V Lithium Cell or Other Energy Source. UL recognized to

1

VBAT ensure against reverse charging when used with a lithium battery. Go to www.maxim-

ic.com/qa/info/ul/.

External SRAM Power Supply Output. This pin is internally connected to VCC when VCC is

2

VCCO within nominal limits. However, during power-fail VCCO is internally connected to the

VBAT pin. Switchover occurs when VCC drops below the lower of VBAT or 2.7V.

3

SCLK Serial Clock Input. Used to synchronize data movement on the serial interface.

4

I/O Data Input/Output. This pin is the bidirectional data pin for the 3-wire interface.

5

CS

Chip Select. Must be asserted high during a read or a write for communication over the 3-

wire serial interface. CS has an internal 40kW pulldown resistor.

6

CEI RAM Chip-Enable In. Must be driven low to enable the external RAM.

7

CEO RAM Chip-Enable Out Low. Active-low chip-enable output for low-order SRAM byte.

8

N.C. No Connection

Interrupt Output. This pin is an active-high output that can be used as an interrupt input to

9

INT

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 DS1677 is powered by VCC or VBAT.

10

GND Ground. DC power is provided to the device on this pin.

11

PFO

Active-Low Power-Fail Output. This pin goes low and sinks current when PFI is less than

1.25V; otherwise this pin remains high.

12

PFI

Active-Low Power-Fail Input. When PFI is less than 1.25V, PFO goes low; otherwise

PFO remains high. Connect PFI to GND or VCC when not used.

Active-Low Reset. The RST pin functions as a microprocessor reset signal. This pin is

driven low 1) when VCC is outside of nominal limits; 2) when the watchdog timer has

13

RST

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 250ms is generated.

This pin has an open-drain output with an internal 47kW pullup resistor.

14,

15, 16

17, 18

19

20

AIN2,

AIN1,

AIN0

X2, X1

VCC

ST

Analog Inputs. These pins are the three analog inputs for the 3-channel ADC.

Connections for Standard 32.768kHz Quartz Crystal. For greatest accuracy, the DS1670

must be used with a crystal that has a specified load capacitance of 6pF. 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, refer to Application Note 58: Crystal

Considerations with Dallas Real Time Clocks. The DS1677 does not function without a

crystal.

+5.0V Input DC Power

Active-Low Strobe Input. The strobe input pin is used with the watchdog timer. If the ST

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

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