FW82801EB Intel, FW82801EB Datasheet - Page 67

• Manufacturer Part Number: FW82801EB
• Manufacturer: Intel

Specifications of FW82801EB

• Lead Free Status / RoHS Status: Not Compliant

2.21.2
2.21.3
2.21.3.1
Intel
®
Figure 2. Example External RTC Circuit
Figure 3. Example V5REF Sequencing Circuit
82801EB ICH5 / 82801ER ICH5R Datasheet
External RTC Circuitry
To reduce RTC well power consumption, the ICH5 implements an internal oscillator circuit that is
sensitive to step voltage changes in VccRTC.
required to condition these voltages to ensure correct operation of the ICH5 RTC.
NOTE: C1 and C2 depend on crystal load.
Power Sequencing Requirements
V5REF / Vcc3_3 Sequencing Requirements
V5REF is the reference voltage for 5 V tolerance on inputs to the ICH5. V5REF must be powered
up before Vcc3_3, or after Vcc3_3 within 0.7 V. Also, V5REF must power down after Vcc3_3, or
before Vcc3_3 within 0.7 V. The rule must be followed in order to ensure the safety of the ICH5. If
the rule is violated, internal diodes will attempt to draw power sufficient to damage the diodes from
the Vcc3_3 rail.
sequencing rule.
This rule also applies to the standby rails, but in most platforms, the VccSus3_3 rail is derived from
the VccSus5 rail; therefore, the VccSus3_3 rail will always come up after the VccSus5 rail. As a
result, V5REF_Sus will always be powered up before VccSus3_3. In platforms that do not derive
the VccSus3_3 rail from the VccSus5 rail, this rule must be comprehended in the platform design.
VccSus3_3
Vbatt
1 kΩ
–
+
Figure 3
To System
Vcc3_3
0.1 µF
100 kΩ
shows a sample implementation of how to satisfy the V5REF/3.3 V
Schottky
Diode
5VREF
32.768 kHz
Xtal
1µF
Figure 2
15 pF
1 µF
C1
shows a schematic diagram of the circuitry
1 KΩ
15 pF
C2
5 V Supply
To System
Signal Description
10 MΩ
R1
VCCRTC
RTCX1
RTCX2
RTCRST#
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