DS1670 Datasheet, PDF (2/16 Pages) Dallas Semiconductor – Portable System Controller

DS1670
DETAILED DESCRIPTION
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 that 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
250ms 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 250ms. 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 timeout.
The DS1670 also provides a 3-channel, 8-bit successive approximation analog-to-digital converter. The
converter has an internal 2.55V (typical) reference voltage generated by an on-board band-gap circuit.
The ADC 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
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