26 FN6659.3 November 22, 2011 discharging to that level. It is strongly advised to monitor the low battery indicators in the status re" />
參數(shù)資料
型號(hào)： ISL12022IBZ
廠商： Intersil
文件頁(yè)數(shù)： 19/29頁(yè)
文件大?。?/td> 0K
描述： IC RTC/CALENDAR TEMP SNSR 8-SOIC
應(yīng)用說(shuō)明： Addressing Power Issues in Real Time Clock Appls
產(chǎn)品培訓(xùn)模塊： Solutions for Industrial Control Applications
標(biāo)準(zhǔn)包裝： 98
類(lèi)型： 時(shí)鐘/日歷
特點(diǎn)： 警報(bào)器，夏令時(shí)，閏年，SRAM
存儲(chǔ)容量： 128B
時(shí)間格式： HH:MM:SS（12/24 小時(shí)）
數(shù)據(jù)格式： YY-MM-DD-dd
接口： I²C，2 線(xiàn)串口
電源電壓： 2.7 V ~ 5.5 V
電壓 - 電源，電池： 1.8 V ~ 5.5 V
工作溫度： -40°C ~ 85°C
安裝類(lèi)型： 表面貼裝
封裝/外殼： 8-SOIC（0.154"，3.90mm 寬）
供應(yīng)商設(shè)備封裝： 8-SOIC
包裝： 管件
產(chǎn)品目錄頁(yè)面： 1245 (CN2011-ZH PDF)
ISL12022
26
FN6659.3
November 22, 2011
discharging to that level. It is strongly advised to monitor the low
battery indicators in the status registers and take action to
replace discharged batteries.
If a supercapacitor is used, it is possible that it may discharge to
below 1.8V during prolonged power-down. Once powered up, the
device may lose serial bus communications until both VDD and VBAT
are powered down together. To avoid that situation, including
situations where a battery may discharge deeply, the circuit in
Figure 20 can be used.
The diode, DBAT will add a small drop to the battery voltage but
will protect the circuit should battery voltage drop below 1.8V.
The jumper is added as a safeguard should the battery ever need
to be disconnect from the circuit.
The VDD negative slew rate should be limited to below the data
sheet spec (10V/ms) otherwise battery switchover can be
delayed, resulting in SRAM contents corruption and oscillator
operation interruption.
Some applications will require separate supplies for the RTC VDD
and the I2C pull-ups. This is not advised, as it may compromise
the operation of the I2C bus. For applications that do require
serial bus communication with the RTC VDD powered down, the
SDA pin must be pulled low during the time the RTC VDD ramps
down to 0V. Otherwise, the device may lose serial bus
communications once VDD is powered up, and will return to
normal operation ONLY once VDD and VBAT are both powered
down together.
Oscillator Crystal Requirements
The ISL12022 uses a standard 32.768kHz crystal. Either through
hole or surface mount crystals can be used. Table 26 lists some
recommended surface mount crystals and the parameters of each.
This list is not exhaustive and other surface mount devices can be
used with the ISL12022 if their specifications are very similar to the
devices listed. The crystal should have a required parallel load
capacitance of 12.5pF and an equivalent series resistance of less
than 50k. The crystal’s temperature range specification should
match the application. Many crystals are rated for -10°C to +60°C
(especially through-hole and tuning fork types), so an appropriate
crystal should be selected if extended temperature range is
required.
Layout Considerations
The crystal input at X1 has a very high impedance, and oscillator
circuits operating at low frequencies (such as 32.768kHz) are
known to pick up noise very easily if layout precautions are not
followed. Most instances of erratic clocking or large accuracy errors
can be traced to the susceptibility of the oscillator circuit to
interference from adjacent high speed clock or data lines. Careful
layout of the RTC circuit will avoid noise pickup and insure accurate
clocking.
Figure 21 shows a suggested layout for the ISL12022 device using
a surface mount crystal. Two main precautions should be followed:
Do not run the serial bus lines or any high speed logic lines in
the vicinity of the crystal. These logic level lines can induce noise
in the oscillator circuit, causing misclocking.
Add a ground trace around the crystal with one end terminated
at the chip ground. This will provide termination for emitted
noise in the vicinity of the RTC device.
In addition, it is a good idea to avoid a ground plane under the X1
and X2 pins and the crystal, as this will affect the load
capacitance and therefore the oscillator accuracy of the circuit. If
the ~IRQ/FOUT pin is used as a clock, it should be routed away
from the RTC device as well. The traces for the VBAT and VDD pins
can be treated as a ground, and should be routed around the
crystal.
FIGURE 20. SUGGESTED BATTERY-BACKUP CIRCUIT
DBAT
CBAT
CIN
BAT43W
0.1F
VDD = 2.7V
TO 5.5V
VBAT = 1.8V
TO 3.2V
JBAT
ISL12022
VDD
GND
VBAT
+
TABLE 26. SUGGESTED SURFACE MOUNT CRYSTALS
MANUFACTURER
PART NUMBER
Citizen
CM200S
Epson
MC-405, MC-406
Raltron
RSM-200S
SaRonix
32S12
Ecliptek
ECPSM29T-32.768K
ECS
ECX-306
Fox
FSM-327
FIGURE 21. SUGGESTED LAYOUT FOR ISL12022 AND CRYSTAL
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