TC648BEOA Microchip Technology, TC648BEOA Datasheet - Page 21

• Manufacturer Part Number: TC648BEOA
• Description: IC PWM FAN SPEED CTRLR SD 8-SOIC
• Manufacturer: Microchip Technology
• Type: Controller - PWM Fanr

Specifications of TC648BEOA

• Applications: Fan Controller, Brushless (BLDC)
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Motor Type: PWM
• No. Of Outputs: 1
• Output Current: 5mA
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 400 uA
• Mounting Style: SMD/SMT
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

FIGURE 5-5:
5.5
The TC646B/TC648B/TC649B is designed to drive an
external NPN transistor or N-channel MOSFET as the
fan speed modulating element. These two arrange-
ments are shown in Figure 5-7. For lower-current fans,
NPN transistors are a very economical choice for the
fan drive device. It is recommended that, for higher cur-
rent fans (300 mA and above), MOSFETs be used as
the fan drive device. Table 5-2 provides some possible
part numbers for use as the fan drive element.
When using a NPN transistor as the fan drive element,
a base current-limiting resistor must be used. This is
shown in Figure 5-7.
When using MOSFETs as the fan drive element, it is
very easy to turn the MOSFETs on and off at very high
rates. Because the gate capacitances of these small
MOSFETs are very low, the TC646B/TC648B/TC649B
can charge and discharge them very quickly, leading to
very fast edges. Of key concern is the turn-off edge of
the MOSFET. Since the fan motor winding is essentially
an inductor, once the MOSFET is turned off the current
that was flowing through the motor wants to continue to
flow. If the fan does not have internal clamp diodes
around the windings of the motor, there is no path for
this current to flow through and the voltage at the drain
of the MOSFET may rise until the drain-to-source rating
of the MOSFET is exceeded. This will most likely cause
the MOSFET to go into avalanche mode. Since there is
very little energy in this occurrence, it will probably not
fail the device, but it would be a long-term reliability
issue.
2003 Microchip Technology Inc.
Output Drive Device Selection
Fan Current During a Locked Rotor Condition.
TC646B/TC648B/TC649B
The following is recommended:
• Ask how the fan is designed. If the fan has clamp
FIGURE 5-6:
Off.
diodes internally, this problem will not be seen. If
the fan does not have internal clamp diodes, it is a
good idea to install one externally (Figure 5-6).
Putting a resistor between V
the MOSFET will also help slow down the turn-off
and limit this condition.
V
OUT
Q
1
: N-Channel MOSFET
Clamp Diode For Fan Turn-
OUT
FAN
GND
and the gate of
R
Q
DS21755B-page 21
SENSE
1