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ISL12058IUZ View Datasheet(PDF) - Intersil

Part NameDescriptionManufacturer
ISL12058IUZ Low Cost and Low Power I2C-Bus? Real Time Clock/Calendar Intersil
Intersil Intersil
ISL12058IUZ Datasheet PDF : 19 Pages
First Prev 11 12 13 14 15 16 17 18 19
Application Section
ISL12058
R/W BIT =“0”
R/W BIT = “1”
SIGNALS S
S
FROM THE T IDENTIFICATION
T IDENTIFICATION
S
MASTER A
BYTE WITH
ADDRESS
A BYTE WITH
A
A
T
R
R/W = 0
BYTE
R
R/W = 1
C
C
O
T
T
K
K
P
SIGNAL AT
SDA
11011110
A
SIGNALS FROM
C
THE SLAVE
K
11011111
A
A
C
C FIRST READ
K
K DATA BYTE
LAST READ
DATA BYTE
FIGURE 11. MULTIPLE BYTES READ SEQUENCE
Oscillator Crystal Requirements
The ISL12058 uses a standard 32.768kHz crystal. Either
through hole or surface mount crystals can be used. Table 8
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 ISL12058 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.
.
TABLE 8. SUGGESTED SURFACE MOUNT CRYSTALS
MANUFACTURER
PART NUMBER
Citizen
CM200S
MicroCrystal
MS3V
Raltron
RSM-200S
SaRonix
32S12
Ecliptek
ECS
ECPSM29T-32.768K
ECX-306
Fox
FSM-327
Figure 12 shows a suggested layout for the ISL12058 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 IRQ/FOUT pin is used as a clock, it should be
routed away from the RTC device as well. The traces for the
VDD pins can be treated as a ground, and should be routed
around the crystal.
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 12. SUGGESTED LAYOUT FOR ISL12058 AND
15
FN6756.0
June 15, 2009
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