ADT7462ACPZ-R7 datasheet(42/81 Pages) ONSEMI

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ADT7462

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Table 24 provides a brief description of each parameter.

Table 24. TMIN Control Loop Parameters

Parameter

Description

TLOW

If the temperature drops below the TLOW limit,

an error flag is set in a status register and an

SMBALERT interrupt can be generated.

THIGH

If the temperature exceeds the THIGH limit, an

error flag is set in a status register and an

SMBALERT interrupt can be generated.

TMIN

The temperature at which the fan turns on

under automatic fan speed control.

Operating

Point

The maximum target temperature for a

particular temperature zone. The system

attempts to maintain system temperature

around the operating point by adjusting the

TMIN parameter of the control loop.

TTHERM

If the temperature exceeds this critical limit, the

fans can be run at 100% for maximum cooling.

TRANGE

Programs the PWM duty cycle vs. temperature

control slope.

Dynamic TMIN Control Programming

Because the dynamic TMIN control mode is a basic

extension of the automatic fan control mode, the automatic

fan control mode parameters should be programmed first

(see Step 1 − Configuring the MUX through Step 8 −

Operating Points for Temperature Channels). Then proceed

with dynamic TMIN control mode programming.

Step 8—Operating Points for Temperature Channels

The operating point for each temperature channel is the

optimal temperature for that thermal zone. The hotter each

zone is allowed to be, the quieter the system, because the fans

are not required to run as fast. The ADT7462 increases or

decreases fan speeds as necessary to maintain the operating

point temperature, allowing for system−to−system variation

and removing the need for worst−case design. If a sensible

operating point value is chosen, any TMIN value can be

selected in the system characterization. If the TMIN value is

too low, the fans run sooner than required, and the

temperature is below the operating point. In response, the

ADT7462 increases TMIN to keep the fans off longer and to

allow the temperature zone to get closer to the operating

point. Likewise, too high a TMIN value causes the operating

point to be exceeded, and in turn, the ADT7462 reduces TMIN

to turn the fans on sooner to cool the system.

Programming the Operating Point Registers

There are two operating point registers, one for the

Remote 1 temperature channel and one for the Remote 2

temperature channel. These 8−bit registers allow the

operating point temperatures to be programmed with 1

°C

resolution.

Operating Point Registers

(100

°C default)

(100

°C default)

Operating Point Hysteresis Register

The operating point hysteresis register sets the value

below the operating point at which TMIN begins to reduce.

°C default)

Step 9—High and Low Limits for Temperature

Channels

The low limit defines the temperature at which the TMIN

value starts to be increased, if temperature falls below this

value. This has the net effect of reducing the fan speed,

allowing the system to get hotter. An interrupt can be

generated when the temperature drops below the low limit.

The high limit should be set above the operating point but

below the critical THERM point. An interrupt can be

generated when the temperature rises above the high limit.

How Dynamic TMIN Control Works

The basic operation of dynamic TMIN control is as

follows:

1. Set the target temperature for the temperature

zone, which could be, for example, the Remote 1

thermal diode. This value is programmed to the

Remote 1 operating point register.

2. As the temperature in that zone rises toward and

exceeds the operating point temperature minus

hysteresis, TMIN is reduced and fan speed

increases.

3. As the temperature drops below the low limit

value, TMIN is increased and the fan speed is

reduced.

Short Cycle and Long Cycle

The ADT7462 implements two loops: a short (or

decrease) cycle and a long (or increase) cycle. The short

cycle takes place every n monitoring cycles. The long cycle

takes place every 2n monitoring cycles. The value of n is

programmable for each temperature channel. The bits are

located at the following register locations.

Dynamic TMIN Control Register 2 (0x0C)

Bits [2:0] (CYR1) = Remote 1

Bits [5:3] (CYR2) = Remote 2

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