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APX9270

Direct PWM Variable Speed Fan Motor Driver

Anpec Electronics 

APX9270

Function Description

Variable Speed Control

The APX9270 is designed with a variable speed control-

ler which has two external input signals, a temperature

signal sensed by a thermistor and an external PWM

signal.

Temperature Speed Control

Using thermistor get temperature to make SET pin voltage.

The fan’s speed is decided by comparing OSC and

SET pin voltage. In addition, the lowest drive duty is

set by comparing the OSC oscillating voltage and MIN

pin voltage (only for temperature speed control side).

Temperature control system works by comparing the

voltage of SET and OSC. When SET voltage is lower than

OSC voltage, one OUT pulled high and another OUT

pulled low. On the contrary, when SET voltage is higher

than OSC voltage, upper side transistors are OFF;

meanwhile, the coil current re-circulates lower side

transistor. Therefore, with decreasing SET voltage, the

output ON-Duty will be increasing, which results in the

increasing of the coil current and motor rotation speed.

External PWM Speed Control

the fan is locked. Connecting the capacitor from CT pin to

GND determines the shutdown time and restart time. As

the fan is locked, the charge/discharge circuit will charge

the CT capacitor to 3.6V by a 2.2µA source current for a

locked detection time, and then the circuit will switch the

capacitor to discharge. During the discharging interval,

the output drivers are switched off until the CT voltage is

discharged to 1.6V by a 0.22µA sink current, and the

circuit will switch the capacitor to charge. In the charging

interval, the IC enters the restart time; one output is high

and another is low, which makes a torque for fan rotation

until the CT voltage is charged to 3.6V by a 2.2µA source

current. If the locked condition still remains, the charge/

discharge process will be recurred until the locked

condition is released (see Figure 2: Lock/Auto Restart

Waveform).

VIN-

VIN+

VOUT2

TOFF

TOFF

VOUT1

TON

This is a pin for the direct PWM speed control. PWM pin

input is pulled down to GND when it is not used. The

VCT

minimum duty is performed by R6 and R7 resistances

(see Typical Application Circuit). R7 is left open if you

want to stop rotation when PWM duty is 0%.

VFG

(see Figure 1: Rotation Control Curve)

OUT -DUTY(%)

External PWM-Duty

Lock Lock

Detection

Release

Figure 2: Lock/Auto Restart Waveform

Duty 100%

Duty 50 %

Duty 0%

TA (oC)

Figure 1: Rotation Control Curve

Lockup Protection and Automatic Restart

The APX9270 provides the lockup protection and auto-

matic restart functions to prevent the coil burnout while

Current Limit

The APX9270 includes both internal and external current

limiters. External current limiter value is programmed by

R which is located between VCC pin and VM pin. The

L

external current limiter works when the voltage difference

between both sides of RL raises to be 0.48V or higher.

For example, the RL=0.5Ω, the external current limiter

value is fixed and internally set at 960mA. The internal

current limiter value is different in rotation mode and lock

mode. It is 1.2A in rotation mode, but it decreases to 0.6A

in lock mode. This feature can reduce power consump-

tion while the fan is locked. In general application, it is

Copyright © ANPEC Electronics Corp.

10

Rev. A.3 - Jun., 2008

www.anpec.com.tw

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