9TCS1083
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 23
9TCS1083 REV 0.8 011612
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 IDT9TCS1083/1085 32.768kHz generator
averaged operation current is less than 2µA.
The coin cell battery with IDT 9TCS1083/1085 VBAT power
pin connection requires 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 PCH/ICH chip and the
9TCS1083/1085 provide seamless power switching
between main V_3.3 and V_bat.
32.768K Clocks Operation
The IDT9TCS1083/1085 32.768K clock output operates in
two modes:
1. When the system is not power ON, V_3.3 is not ready and
IDT 9TCS1083 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 9TCS1083 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 to 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
100ohm
10~22uF
9TCS1083
Power Switch
V_3.3
1uf
Single Trace impedance Length Notes
X1 50 ohm 6 inches
X2 50 ohm 6 inches
