DS1670 Datasheet, PDF (3/16 Pages) Dallas Semiconductor – Portable System Controller

DS1670
PIN DESCRIPTION
PIN NAME
FUNCTION
Battery Input for Standard 3V Lithium Cell or Other Energy Source. UL recognized to
1
V_BAT 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 V_CC when V_CC is
2
V_CCO within nominal limits. However, during power-fail V_CCO is internally connected to the
V_BAT pin. Switchover occurs when V_CC drops below the lower of V_BAT 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
CEOL RAM Chip-Enable Out Low. Active-low chip-enable output for low-order SRAM byte.
8
CEOH RAM Chip-Enable Out High. Active-low chip-enable output for high-order SRAM byte.
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 DS1670 is powered by V_CC or V_BAT.
10
GND Ground. DC power is provided to the device on this pin.
11
BHE
Byte High-Enable Input. This pin when driven low activates the CEOH output if CEI is
also driven low.
12
BLE
Byte Low-Enable Input. This pin when driven low activates the CEOL output if CEI is
also driven low.
Active-Low Reset. The RST pin functions as a microprocessor reset signal. This pin is
driven low 1) when V_CC 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
V_CC
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 DS1670 does not function without a
crystal.
+3.3V Input DC Power. When 3.3V is applied within nominal limits, the device is fully
accessible and data can be written and read. When V_CC drops below 2.88V (typical) access
to the device is prohibited. When V_CC drops below the lower of V_BAT and 2.7V (typical),
the device is switched over to the backup power supply.
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.
3 of 16