FW82801DB S L66K Intel, FW82801DB S L66K Datasheet - Page 54

• Manufacturer Part Number: FW82801DB S L66K
• Manufacturer: Intel

Specifications of FW82801DB S L66K

• Lead Free Status / RoHS Status: Supplier Unconfirmed

Signal Description
2.20.2
2.20.3
54
Figure 2-2. Example External RTC Circuit
External RTC Circuitry
To reduce RTC well power consumption, the ICH4 implements an internal oscillator circuit that is
sensitive to step voltage changes in VccRTC and VBIAS.
the circuitry required to condition these voltages to ensure correct operation of the ICH4 RTC.
V5REF / Vcc3_3 Sequencing Requirements
V5REF is the reference voltage for 5 V tolerance on inputs to the ICH4. 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 ICH4. 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 and 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.
NOTES:
1. Reference designators arbitrarily assigned.
2. 3.3 V VccSus is active when system plugged in.
3. Vbatt is voltage provided by battery.
4. VBIAS, VccRTC, RTCX1, and RTCX2 are Intel
5. VBIAS is used to bias the ICH4 internal oscillator.
6. VccRTC powers the RTC well of the ICH4.
7. RTCX1 is the input to the internal oscillator.
8. RTCX2 is the feedback for the external crystal.
9. C1 and C2 depend on crystal load.
VccSus
3.3 V
Vbatt
1 k
Figure 2-3
shows a sample implementation of how to satisfy the V5REF/3.3 V
0.047 uF
C3
32.768 kHz
Xtal
®
1 F
ICH4 pins.
18 pF
C1
Figure 2-2
18 pF
C2
Intel
shows a schematic diagram of
®
82801DB ICH4 Datasheet
R1
10 M
R2
10 M
RTC_osc_circ
VccRTC
RTCX2
RTCX1
VBIAS