TC651ADVUA(2004) データシートの表示（PDF） - Microchip Technology

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TC651ADVUA
(Rev.:2004)

Tiny Integrated Temperature Sensor & Brushless DC Fan Controller with Over-Temperature Alert

Microchip Technology 

4.0 DETAILED DESCRIPTION

The TC650/TC651 acquire and convert their junction

temperature (TJ) information from an on-chip, solid-

state sensor with a typical accuracy of ±1°C. The tem-

perature data is digitally stored in an internal register.

The register is compared with pre-defined threshold val-

ues. The six threshold values are equally distributed

over a pre-defined range of temperatures (see Table 4-

1). The TC650/TC651 control the speed of a DC brush-

less fan using a fractional speed-control scheme. The

output stage requires only a 2N2222-type, small-signal

BJT for fans up to 300 mA. For larger current fans (up

to 1 amp), a logic-level N-channel MOSFET may be

used. In addition to controlling the speed of the fan, the

TC650/TC651 include an on-chip overtemperature

alarm (TOVER) that gives a low signal when the temper-

ature of the chip exceeds TH by 10°C (typical). This fea-

ture eliminates the need for a separate temperature

sensor for overtemperature monitoring. Figure 4-1

shows the block diagram of the device.

VDD

TOVER SHDN

Temperature

Set Point and

Trim Range

Duty Cycle

Logic

Control

A/D Converter

Oscillator

Temperature Sensor

V+

PWM

FIGURE 4-1:

Functional Block Diagram.

4.1 PWM Output

The PWM pin is designed to drive a low-cost transistor

or MOSFET as the low-side, power-switching element

in the system. This output has an asymmetric

complementary drive and is optimized for driving NPN

transistors or N-channel MOSFETs. Since the system

relies on PWM rather than linear power control, the

dissipation in the power switch is kept to a minimum.

Generally, very small devices (TO-92 or SOT

packages) will suffice. The frequency of the PWM is

about 15 Hz. The PWM is also the time base for the

Start-up Timer (see Section 4.2 “Start-Up Timer”).

The PWM duty cycle has a range of 40% to 100% for

the TC650 and 50% to 100% for the TC651.

TC650/TC651

4.2 Start-Up Timer

To ensure reliable fan start-up, the Start-up Timer turns

PWM high for about 2 seconds whenever the fan is

started from the off state. This occurs at power-up and

when coming out of Shutdown mode.

4.3 Overtemperature Alert (TOVER)

This pin goes low when the TH set point is exceeded by

10°C (typical). This indicates that the fan is at

maximum drive and the potential exists for system

overheating; either heat dissipation in the system has

gone beyond the cooling system's design limits or

some fault exists (such as fan bearing failure or an air-

flow obstruction). This output may be treated as a

“System Overheat” warning and be used to either

trigger system shutdown or bring other fans in the

system to full speed. The fan will continue to run at full

speed while TOVER is asserted. Built-in hysteresis

prevents TOVER from “chattering” when the measured

temperature is at or near the TH + 10°C trip point. As

temperature falls through the TH + 10°C trip point, hys-

teresis maintains the TOVER output low until the

measured temperature is 5°C above the trip point

setting.

4.4 Shutdown (SHDN)

The fan can be unconditionally shut down by pulling

the SHDN pin low. During shutdown, the PWM output

is low; ideal for notebook computers and other portable

applications where you need to change batteries and

must not have the fan running at that time. Thermal

monitoring and TOVER are still in operation during

shutdown. IDD shutdown current is around 50 µA.

4.5 Auto-shutdown Mode

The TC651 features auto-shutdown. When the

temperature is below the factory set point at minimum

speed (TL), PWM is low and the fan is automatically

shut off (Auto-shutdown mode). This feature is ideal for

notebook computers and other portable equipment that

need to conserve as much battery power as possible

and, thus, run a fan when it is only absolutely needed.

The TC651 will continue to be active in order to monitor

temperature for TOVER. The TC651 exits Auto-

shutdown mode when the temperature rises above the

factory set point (T1).

 2004 Microchip Technology Inc.

DS21450C-page 7

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