Toshiba TDP-D1, Service Manual

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The Fan control IC also contains a 2-channel fan speed controller. It connects directly to the
fans and performs closed-loop control of the fan speed independently. The only external component
required is a 10µF capacitor per channel. It determines the current fan speed based on the fan
rotation pulses and an externally supplied 32.768KHz clock.
It uses pulse width modulation (PWM) method and an on-chip MOSFET to control the fan
speed to ±2% of the programmed speed. The desired fan speed is also programmed via SMBusTM.
The actual fan speed and fan status can be ead via the SMBusTM. Short-circuit protection is
implemented to prevent damages to the fan and this IC itself. The accepted frequency of fan rotation
pulses is 100~1000Hz, which corresponds to 3,000 to 30,000 rpm for a typical fan that produces two
pulses per revolution. The IC also turns on the fans by hardware watchdog system. The fan controller
would fully turn on both fans when one of the following conditions happens.
1. when either of the remote temperature is higher than its own TMAX.
2.when either of these two remote diodes is open.
3.when both remote diodes are short
Figure 7. Fan Control IC Operating Circuit