TC646B Datasheet, PDF (1/36 Pages) Microchip Technology – PWM Fan Speed Controllers With Auto-Shutdown, Fan Restart and FanSense™ Technology for Fault Detection

M TC646B/TC648B/TC649B
PWM Fan Speed Controllers With Auto-Shutdown, Fan
Restart and FanSense™ Technology for Fault Detection
Features
• Temperature-Proportional Fan Speed for Acoustic
Noise Reduction and Longer Fan Life
• Efficient PWM Fan Drive
• 3.0V to 5.5V Supply Range:
- Fan Voltage Independent of TC646B/
TC648B/TC649B Supply Voltage
- Supports any Fan Voltage
• FanSense^™ Fault Detection Circuit Protects
Against Fan Failure and Aids System Testing
(TC646B/TC649B)
• Automatic Shutdown Mode for “Green” Systems
• Supports Low Cost NTC/PTC Thermistors
• Over-Temperature Indication (TC646B/TC648B)
• Fan Auto-Restart
• Space-Saving 8-Pin MSOP Package
Applications
• Personal Computers & Servers
• LCD Projectors
• Datacom & Telecom Equipment
• Fan Trays
• File Servers
• General-Purpose Fan Speed Control
Package Types
MSOP, PDIP, SOIC
V_IN 1
C_F 2
V_AS 3
GND 4
TC646B
TC649B
8 V_DD
7 V_OUT
6 FAULT
5 SENSE
Description
The TC646B/TC648B/TC649B devices are new ver-
sions of the existing TC646/TC648/TC649 fan speed
controllers. These devices are switch-mode fan speed
controllers that incorporate a new fan auto-restart func-
tion. Temperature-proportional speed control is accom-
plished using pulse width modulation. A thermistor (or
other voltage output temperature sensor) connected to
the V_IN input supplies the required control voltage of
1.20V to 2.60V (typical) for 0% to 100% PWM duty
cycle. The auto-shutdown threshold/temperature is set
by a simple resistor divider on the V_AS input. An inte-
grated Start-Up Timer ensures reliable fan motor start-
up at turn-on, coming out of shutdown mode, auto-
shutdown mode or following a transient fault. A logic
low applied to V_IN (pin 1) causes fan shutdown.
The TC646B and TC649B also feature Microchip
Technology's proprietary FanSense technology for
increasing system reliability. In normal fan operation, a
pulse train is present at SENSE (pin 5). A missing-
pulse detector monitors this pin during fan operation. A
stalled, open or unconnected fan causes the TC646B/
TC649B device to turn the V_OUT output on full (100%
duty cycle). If the fan fault persists (a fan current pulse
is not detected within a 32/f period), the FAULT output
goes low. Even with the FAULT output low, the V_OUT
output is on full during the fan fault condition in order to
attempt to restart the fan. FAULT (TC646B) or OTF
(TC648B) is also asserted if the PWM reaches 100%
duty cycle, indicating that maximum cooling capability
has been reached and a possible overheating condition
exists.
The TC646B, TC648B and TC649B devices are avail-
able in 8-pin plastic MSOP, SOIC and PDIP packages.
The specified temperature range of these devices is
-40 to +85ºC.
V_IN 1
C_F 2
V_AS 3
GND 4
TC648B
8 V_DD
7 V_OUT
6 OTF
5 NC
 2003 Microchip Technology Inc.
DS21755B-page 1