Dell 3521 LA-9104p Fan Controller APE8873M

Fan Controller icLaptops are very important part of anyone’s  life. If it out of order our speedy life feels like stuck.So to keep laptop healthy by service it every three months. usually, laptops are out of order by dust and choking fan and damage Fan Controller, Normally its ok by removing dust and grease fan.but if a fault in PCB circuit then we have to understand how the circuit works.So let’s go for circuit understanding.

Fan controller APE8873M fundamental

Fan Controller circuitAs we can see 5 to 8 pins are ground. pin 1 and 2 are input generally 5v. Pin3 is voltage output which is 1.6 times higher than the voltage set on pin no.4 named VSET.

In Dell 3521 VIN and EN pin are same input from 5vs for internal logic supply and thermal section.Enable pin is by default set to enable by setting it to high (5vs).So when the VSET pin Gets input pulse From EC ( EN_DFAN1) the output generated to fan and fan gives the speed output to EC (FAN_SPEED1). This is the feedback signal of fan PWM output. it will compare the speed and check if the current speed is higher or lower than the expected one. If slower, the controller will increase the frequency to drive EN_DFAN1 automatically, otherwise decrease the frequency. The expected speed can be programmable by F/W.


Fan ControllerThe fan controller can be used to control 12-bit PWM channel called FAN PWM. While Fixed-FAN mode enables and PWM function applied, the fan controller will refer to the peripheral clock (33MHz) and the PWM high period and cycle time can be determined by the following formula:
PWM Cycle Length = (PWM cycle register + 1 ) * peripheral clock resolution
PWM High Period = (PWM high period register + 1 ) * peripheral clock
Duty Cycle = (PWM high period register +1) / (PWM cycle register +1)

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