DS28DG02 Datasheet, PDF (15/34 Pages) Dallas Semiconductor – 2kb SPI EEPROM with PIO, RTC, Reset, Battery Monitor, and Watchdog

DS28DG02: 2Kb SPI EEPROM with PIO, RTC, Reset, Battery Monitor, and Watchdog
MONITORING FUNCTIONS
The DS28DG02 has two voltage monitors: one for the V_CC supply voltage and another one for the battery that
supplies the RTC and associated registers if V_CC is switched off. If V_CC falls below the V_TRIP threshold the V_CC
monitor activates the open-drain RSTZ output, as shown in Figure 6. There is a delay of t_DEL between crossing the
trip point and RSTZ going LOW. As long as V_CC is above V_POR or the device has a functioning battery backup, the
logic level at RSTZ does not exceed V_OLmax. Without battery support, the state of the RSTZ output is undefined for
V_CC values below V_POR. When V_CC ramps up, RSTZ remains at LOW until the V_TRIP threshold is reached. As V_TRIP is
crossed, the voltage at RSTZ rises until it reaches V_TRMS, the manual reset release threshold. This activates the
debounce circuit, which holds RSTZ low for t_RST. After t_RST is expired, the voltage at RSTZ ramps up to the value of
the applied pullup voltage.
Figure 6. RSTZ Power-Fail Reset
V_CC
V_TRIP
V_POR
V_CC ^*
RSTZ
t_DEL
t_RST
With the VBAT pin tied to VCC, the RSTZ behavior for
*^{VVCCCC<oVr P}_t^O_h^R_e
is undefined.
applicable pullup
voltage
for
the
RSTZ
pin.
As VTRIP is crossed, the voltage at
RSTZ starts rising, which triggers
the manual switch debounce
circuit and activates RSTZ for tRST.
The RSTZ pin is internally connected to a debounce circuit, which allows using a manually operated switch to
generate a reset signal. Figure 7 illustrates the timing of the manual reset. As the switch closes, it forces the
voltage at RSTZ to fall below V_ILmax, which triggers the debounce circuit. Now the voltage at RSTZ is held at logic
LOW by both, the manual switch and the debounce circuit. When the manual switch is opened or t_DEB is over,
(whichever occurs later) the voltage at RSTZ rises until it reaches V_TRMS. This again triggers the debounce circuit,
which holds RSTZ low for t_RST, after which the voltage at RSTZ ramps up to the pullup voltage. The minimum LOW
time of a manually generated reset is t_DEB + t_RST.
Figure 7. RSTZ Manual Switch Debounce
Open
Manual
Switch
closed
V_CC ^*
RSTZ
V_TRMS
RSTZ held low by
DS28DG02
t_DEB
RSTZ held low
by manual switch
t_RST
F_{* VorCC}tR_oST_r
to start, the voltage at RSTZ
the applicable pullup voltage
has to
for the
cross VTRMS
RSTZ pin.
after
tDEB
is
expired.
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