TC654EUN Microchip Technology, TC654EUN Datasheet - Page 22

• Manufacturer Part Number: TC654EUN
• Description: IC PWM FAN SPEED CTRLR 10-MSOP
• Manufacturer: Microchip Technology
• Type: High Speed PWM Controllerr

Specifications of TC654EUN

• Number Of Outputs: 1
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Applications: Fan Controller, Brushless (BLDC)
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Output Current: 5 mA (Min)
• Operating Supply Voltage: 3 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Motor Type: PWM
• No. Of Outputs: 1
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: MSOP
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +85°C
• 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

TC654/TC655
7.0
7.1
The SMBus is an open collector bus, requiring pull-up
resistors connected to the SDA and SCLK lines. This
configuration is shown in Figure 7-1.
FIGURE 7-1:
SMBus.
The number of devices connected to the bus is limited
only by the maximum rise and fall times of the SDA
and SCLK lines. Unlike I
does not specify a maximum bus capacitance value.
Rather, the SMBus specification calls out that the max-
imum current through the pull-up resistor be 350 µA
(minimum, 100 µA, is also specified). Therefore, the
value of the pull-up resistors will vary depending on the
system’s bias voltage, V
tance is still very important as it directly effects the rise
and fall times of the SDA and SCLK lines. The range
for pull-up resistor values for a 5 V system are shown
in Figure 7-1.
Although SMBus specifications only require the SDA
and SCLK lines to pull down 350 µA, with a maximum
voltage drop of 0.4 V, the TC654/TC655 has been
designed to meet a maximum voltage drop of 0.4 V,
with 3 mA of current. This allows lower values of pull-
up resistors to be used, which will allow higher bus
capacitance. If this is to be done, though, all devices on
the bus must be able to meet the same pull down
current requirements as well.
A possible configuration using multiple devices on the
SMBus is shown in Figure 7-2.
DS21734A-page 22
Range for R: 13.2 k to 46 k
APPLICATIONS INFORMATION
Connecting to the SMBus
V
R
DD
Pull-up Resistors On
DD
R
2
C specifications, SMBus
. Minimizing bus capaci-
TC654/TC655
SDA
SCLK
for V
DD
= 5.0 V
FIGURE 7-2:
7.2
The PWM frequency of the V
capacitor value attached to the C
quency will be 30 Hz (typical) for a 1 µF capacitor. The
relationship between frequency and capacitor value is
linear, making alternate frequency selections easy.
As stated in previous sections, the PWM frequency
should be kept in the range of 15 Hz to 35 Hz. This will
eliminate the possibility of having audible frequencies
when varying the duty cycle of the fan drive.
A very important factor to consider when selecting the
PWM frequency for the TC654/TC655 devices is the
RPM rating of the selected fan and the minimum duty
cycle that you will be operating at. For fans that have a
full speed rating of 3000 RPM or less, it is desirable to
use a lower PWM frequency. A lower PWM frequency
allows for a longer time period to monitor the fan cur-
rent pulses. The goal is to be able to monitor at least
two fan current pulses during the on time of the V
output.
Example: Your system design requirement is to oper-
ate the fan at 50% duty cycle when ambient tempera-
tures are below 20°C. The fan full speed RPM rating is
3000 RPM and has four current pulses per rotation. At
50% duty cycle, the fan will be operating at approxi-
mately 1500 RPM.
EQUATION
If one fan revolution occurs in 40 msec, then each fan
pulse occurs 10 msec apart. In order to detect two fan
current pulses, the on time of the V
at least 20 msec. With the duty cycle at 50%, the total
period of one cycle must be at least 40 msec, which
makes the PWM frequency 25 Hz. For this example, a
PWM frequency of 20 Hz is recommended. This would
define a C
Time for one revolution (msec.)
Microcontroller
Setting the PWM Frequency
PIC16F876
F
TC654/TC655
Fan Speed
Controller
capacitor value of 1.5 µF.
Multiple Devices on SMBus.
SDA SCLK
2002 Microchip Technology Inc.
OUT
=
F
output is set by the
Temperature
pin. The PWM fre-
OUT
60
----------------------- -
EEPROM
24LC01
TCN75
Sensor
1500
pulse must be
1000
=
40
OUT