9TCS1085
MOBILE ACCESS™—CLOCK SYNTHESIZER, TEMPERATURE SENSOR, & PWM FAN CONTROLLER FOR PORTABLE DEVICES
IDT®
MOBILE ACCESS™—CLOCK SYNTHESIZER, TEMPERATURE SENSOR, & PWM FAN CONTROLLER FOR PORTABLE DEVICES 22
9TCS1085 REV 0.7 012012
Frequency Generator 32.768 kHz
Recommended 25MHz Quartz Crystal
Specifications
SMD 25MHz AT cut crystal and maximum driver level at
100µW, for example TXC.
VBAT Battery Recommendations and
Connection Considerations
Recommended to use coin cell battery CR2032, CR2025 or
equivalent.
The normal coin cell battery storage capacity is 170 mAh to
220mAh and the average total RTC circuit current required
5uA, the battery life will be at least:
170,000 µAh / 5 µA = 34,000 hours = 3.88 years
The RTC circuit (PCH) usually consumes 3µA power, thus
the 32.768kHz clock generator circuit needs be less than
2µA. The 9TCS1085 32.768kHz generator averaged
operation current is less than 2µA.
The coin cell battery with 9TCS1085 VBAT power pin
connection required a 100 ohm and 22µF ceramic capacitor
current limitation and noise filtering. The RC needs to be
added to the battery to limit the current spikes effects.
The VDD_RTC connect to the Intel ICH chip and the
9TCS1085 provide seamless power switching between
main V_3.3 and V_bat.
32.768K Clocks Operation
The 9TCS1085 32.768K clock output operates in two
modes:
1. When the system is not power ON, V_3.3 is not ready and
9TCS1085 is powered with the coin cell battery. The 32kHz
comes from the DCO with the digital calibration to keep the
accuracy.
2. After V_3.3 is ready, the 9TCS1085 creates a seamless
switch power from V_bat to V_3.3 and the calibration will go
to full speed: this will happen every 2~3ms to keep the
accuracy and the 32K source will be switched to 25MHz
oscillator with Fraction-N divider to get the 0ppm.
32.768K DCO uses a 25Mhz crystal oscillator for calibration
reference, thus the 25MHz oscillator must be fine tuned in
order to get the best 32.768kHz accuracy.
RTC Routing Guidelines
V_bat
VDD_RTC
CR2032H
100
10~22uF
9TCS1085
Power Switch
V_3.3
1uf
ace impedan
Length Notes
X1 50 ohm 6 inches
X2 50 ohm 6 inches
