MAX1358B Maxim Integrated Products, MAX1358B Datasheet - Page 30

• Manufacturer Part Number: MAX1358B
• Description: Data-Acquisition System
• Manufacturer: Maxim Integrated Products

DataSheet.in
The on-chip oscillator requires an external crystal (or
resonator) connected between 32KIN and 32KOUT
with a 32.768kHz operating frequency. This oscillator is
used for the RTC, alarm, PWM, watchdog, charge
pump, and FLL. In any crystal-based oscillator circuit,
the oscillator frequency is sensitive to the capacitive
load (C
from the oscillator circuit and not the capacitance of the
crystal. The input capacitance across 32KIN and
32KOUT is 6pF. Choose a crystal with a 32.768kHz
oscillation frequency and a 6pF capacitive load such
16-Bit, Data-Acquisition System with ADC, DACs,
UPIOs, RTC, Voltage Monitors, and Temp Sensor
Figure 7. DV
Figure 8. CPOUT Voltage-Supervisor Block Diagram
30
______________________________________________________________________________________
WDTO
L
). C
CPDE
DD
CPOUT
L
Voltage-Supervisor Block Diagram
is the capacitance that the crystal needs
LSDE
DV
DD
CPOUT (2.7V) VOLTAGE MONITOR
2.7VTH
1.8VTH
2.0VTH
1.25V
ANALOG
2:1 MUX
Crystal Oscillator
CMP
CPDE
1.25V
LCPD
CMP
LSDE
HYSE POR
CONTROL
as the C-002RX32-E from Epson Crystal. Using a crys-
tal with a C
the oscillator circuit causes the oscillator to run faster
than the specified nominal frequency of the crystal or to
not start up. See Figures 9 and 10 for block diagrams
of the crystal oscillator and the CLK32K I/O.
The integrated RTC provides the current time information
from a 32-bit counter and subsecond counts from an
8-bit ripple counter. An internally generated reference
clock of 256Hz (derived from the 32.768kHz crystal) dri-
ves the 8-bit subsecond counter. An overflow of the 8-bit
subsecond counter inputs a 1Hz clock to increment the
32-bit second counter. The RTC 32-bit second counter is
translatable to calendar format with firmware. All 40 bits
(32-bit second counter and 8-bit subsecond counter)
must be clocked in or out for valid data. The RTC and
the 32.768kHz crystal oscillator consume less than 1µA
when the rest of the device is powered down.
Program the AL_DAY register with a 20-bit value, which
corresponds to a time 1s to 12 days later than the cur-
rent time with a 1s resolution. The alarm status bit, ALD,
asserts when the 20 bits of the AL_DAY register match-
es the 20 LSBs of the 32-bit second counter. The ADE
bit automatically clears when the time-of-day alarm
trips. The time-of-day alarm causes the device to exit
sleep mode.
LOGIC
RSTE
L
that is larger than the load capacitance of
DV
DD
(1.8V) VOLTAGE MONITOR
Real-Time Clock (RTC)
Time-of-Day Alarm
LDVD
RESET