Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF HTML

MAX6640 Datasheet(PDF) 16 Page - Maxim Integrated Products

Part No. MAX6640
Description  2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
Download  21 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
Logo 

MAX6640 Datasheet(HTML) 16 Page - Maxim Integrated Products

Zoom Inzoom in Zoom Outzoom out
 16 / 21 page
background image
Applications Information
Fan-Drive Circuits
A variety of fan-drive circuit configurations can be used
with the MAX6640 to control the fan’s speed. Four of
the most common are shown in Figures 6 through 10.
PWM Power-Supply Drive (High Side or Low Side)
The simplest way to control the speed of a 3-wire (sup-
ply, ground, and tachometer output) fan is to modulate
its power supply with a PWM signal. The PWM frequen-
cy is typically in the 20Hz to 40Hz range, with 33Hz
being a common value. If the frequency is too high, the
fan’s internal control circuitry does not have sufficient
time to turn on during a power-supply pulse. If the fre-
quency is too low, the power-supply modulation
becomes more easily audible.
The PWM can take place on the high side (Figure 6) or
the low side (Figure 7) of the fan’s power supply. In
either case, if the tachometer is used, it is usually nec-
essary to periodically stretch a PWM pulse so there is
enough time to count the tachometer pulse edges for
speed measurement. The MAX6640 allows this pulse
stretching to be enabled or disabled to match the
needs of the application.
Pulse stretching can sometimes be audible if the fan
responds quickly to changes in the drive voltage. If the
acoustic effects of pulse stretching are too noticeable,
the circuit in Figure 8 can be used to eliminate pulse
stretching while still allowing accurate tachometer feed-
back. The diode connects the fan to a low-voltage
power supply, which keeps the fan’s internal circuitry
powered even when the PWM drive is zero. Therefore,
the tachometer signal is always available and pulse
stretching can be turned off. Note that this approach
prevents the fan from turning completely off, so even
when the duty cycle is 0%, the fan may still spin.
Linear Fan Supply Drive
While many fans are compatible with PWM power-supply
drive, some are excessively noisy with this approach.
When this is the case, a good alternative is to control the
fan’s power-supply voltage with a variable DC power-sup-
ply circuit. The circuit in Figure 9 accepts the PWM signal
as an input, filters the PWM, and converts it to a DC volt-
age that then drives the fan. To minimize the size of the fil-
ter capacitor, use the highest available PWM frequency.
Pulse stretching is not necessary when using a linear fan
supply. Note that this approach is not as efficient as PWM
drive, as the fan’s power-supply current flows through the
MOSFET, which can have an appreciable voltage across
it. The total power is still less than that of a fan running
at full speed. Table 10 is a summary of fan-drive
options.
2-Channel Temperature Monitor with Dual
Automatic PWM Fan-Speed Controller
16
______________________________________________________________________________________
D[7:6]
TACHOMETER PULSES PER
REVOLUTION
00
1
01
2
10
3
11
4
Table 9. Tachometer Pulses per
Revolution
VCC
PWM1
4.7k
4.7k
TACH1
3V TO 5.5V
TACH
OUTPUT
VFAN
(5V OR 12V)
Figure 6. High-Side PWM Drive Circuit
VCC
TACH1
4.7k
4.7k
PWM1
3V TO 5.5V
3V TO 5.5V
TACH
OUTPUT
VFAN
(5V OR 12V)
Figure 7. Low-Side Drive Circuit


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21 


Datasheet Download




Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn