DS1670 Datasheet, PDF (2/17 Pages) Dallas Semiconductor – Portable System Controller

DS1670
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_CC. When an out-of-
tolerance condition occurs, an internal power-fail signal is generated which forces the reset to the active
state. When V_CC 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
V_CC, GND - DC power is provided to the device on these pins. V_CC 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_CC drops below 2.88 volts (typical) access to the device is prohibited. When V_CC drops below the
lower of V_BAT and 2.7 volts (typical), the device is switched over to the backup power supply.
V_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.
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