25 FN6682.3 December 6, 2011 The diode, DBAT will add a small drop to t" />
參數(shù)資料
型號(hào)： ISL12023IVZ
廠商： Intersil
文件頁(yè)數(shù)： 18/29頁(yè)
文件大?。?/td> 0K
描述： IC RTC/CLDR TEMP SNSR 14-TSSOP
產(chǎn)品培訓(xùn)模塊： Solutions for Industrial Control Applications
標(biāo)準(zhǔn)包裝： 960
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： 14-TSSOP（0.173"，4.40mm 寬）
供應(yīng)商設(shè)備封裝： 14-TSSOP
包裝： 管件
ISL12023
25
FN6682.3
December 6, 2011
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.
Oscillator Crystal Requirements
The ISL12023 uses a standard 32.768kHz crystal. Either through
hole or surface mount crystals can be used. Table 28 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 ISL12023 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 20 shows a suggested layout for the ISL12023 device
using a surface mount crystal. Two main precautions should be
followed:
1. 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 to cause misclocking.
2. 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 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.
Crystal Oscillator Frequency Compensation
CRYSTAL CHARACTERISTICS
The ISL12023 device contains a complete system for adjusting
the frequency of the crystal oscillator to compensate for
temperature variation. A typical 32.768kHz crystal used with RTC
devices has a temperature versus frequency curve, as shown in
Figure 21.
This curve equation follows Equation 6:
Where
α is the temperature constant, with a typical value of
0.034 ppm/°C.
T0 is the turnover temperature of the crystal, which is the apex of
the parabolic curve. If the two factors
α and T0 are known, it is
possible to correct for crystal temperature error to very high
accuracy.
The crystal will have an initial accuracy error at room
temperature, typically specified at ±20°C. The other important
TABLE 28. 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 19. SUGGESTED BATTERY-BACKUP CIRCUIT
DBAT
CBAT
CIN
BAT43W
0.1F
VDD = 2.7V
TO 5.5V
VBAT = 1.8V
TO 3.2V
JBAT
ISL12023
VDD
GND
VBAT
+
FIGURE 20. SUGGESTED LAYOUT FOR ISL12023 AND CRYSTAL
TEMPERATURE (°C)
-160
-140
-120
-100
-80
-60
-40
-20
0
-40 -30 -20 -10 0 102030 40 50607080
PP
M
FIGURE 21. RTC CRYSTAL TEMPERATURE DRIFT
Δf
α
T
(
T0)
2
–
=
(EQ. 6)
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