Hello Eli,
To answer your questions:
1. Is it possible to have 10 units tied serially?
- The AMC6821 has two address bits, making it capable to share 4 devices on one I2C Bus. To increase the number of devices on one I2C bus, you may need some kind of multiplexing scheme as there are only a maximum of 4 unique slave addresses.
2. What is the difference between Thermal mode and DCY mode?
- To clarify this question it should be noted that the AMC6821 has three fan control modes: Auto Temperature-Fan mode, Software-RPM mode, and Software-DCY mode.
- Both Auto Temp and Software RPM are closed-loop control, meaning that when all parameters are defined the modes allow the device to run as a stand-alone device without CPU intervention.
- Software-DCY is open-loop. In Software-DCY mode, the PWM duty cycle is set directly by the value written to the device.
3. Can the user set the spin-up operation at startup to 60% instead of 100%?
- The Fan Spin-Up is hard programmed to increase from 33.3% to 100% duty cycle, and then maintains this value for the remainder of the spin-up process. This spin-up time duration can be changed by editing the STIME bits -- the time can be changed from 0.2 seconds to 8 seconds. After the spin-up process completes, the fan speed is controlled normally through the register value (DCY mode) or via closed loop (Temp and Software RPM mode).
- Spin-up can also be disabled by setting the FSPD bit of the Fan Characteristics Register to '1'.
4. Alarm bit clarification
- When the TACH is set and both the TACH high limit and low limit have been programmed the fan-out-of-range interrupt can be enabled allowing the device to monitor that data from the TACH and when the speed is above or below it's defined limits it will generate an alarm that asserts the /SMBALERT pin to active low. (pg 19 of DS). A complete block diagram is listed on page 32 of the DS, which describes the register settings with block logic.
5. Percentage Speed Fan failure
- The fan speed limits can be programmed into the TACH-High-Limit, and TACH-Low-Limit. Therefore you can adjust the percentages and apply to these registers.
6. After Spin-up
- In Software-DCY mode (open-loop) the PWM output duty cycle changes to the target value (user input to 0x22) immediately after the user writes the desired duty cycle to the device registers.
- In Auto Temp-Fan Control mode, the AMC6821 runs stand-alone (closed-loop), and the mode optimizes fan sppeed for a given temperature to intelligently manage the system.
- In Software RPM, the AMC6821 runs stand-alone (closed-loop), and works as a fan speed regulator to maintain the speed at a programmable target value.
Best Regards,
Matt