Microchip MEC1428 Bedienungsanleitung


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 2017 Microchip Technology Inc. DS00002137B-page 1
INTRODUCTION
Pulse Width Modulation (PWM) modules, which produce basically digital waveforms, can be used in many applications
as a more efficient and lower power alternative to the traditional 8 bit Digital-to-Analog (D/A) converters using only two
inexpensive filter components. A wide variety of microcontroller applications that exist today are better served by utiliz-
ing a PWM generated analog output as opposed to an 8 bit D/A converter. One application where using a high resolution
PWM has value vs. a traditional 8 Bit DAC is in driving the 3-wire voltage controlled fan in a PC.
Audience
This document is written for a reader that is familiar with hardware design. The goal of this application note is to provide
information regarding how to use a PWM to drive 3-wire fans that provides system benefits and an enhanced customer
experience.
References
The following documents should be referenced when using this application note. Please contact your Microchip repre-
sentative for availability.
• Microchip MEC140x/MEC141x/MEC142x Data Sheet
• Microchip MEC140x/MEC141x/MEC142x EVBs
AN2137
PWM Controlled Fan for MEC140x/MEC141x/MEC142x
Author: Tom Tse / Greg VanWesten

Microchip Technology Inc.
AN2137
DS00002137B-page 2  2017 Microchip Technology Inc.
1.0 OVERVIEW
Key potential benefits of using a high resolution PWM generated analog output for 3 wire fan control include:
• Finer RPM resolution (4x) control vs a traditional 8 bit DAC.
• Finer RPM control can potentially solve the issue of having two consumer platforms at the same thermal condition
each running at a different RPM Zoned speed – since the finer control would allow you to control RPM closer to
mechanical resonant points of the box and thus significantly reduce the chance of one machine running at differ-
ent binned zone speeds).
The purpose of this white paper is to show the benefits of using the MEC140x/MEC141x/MEC142x 16 bit PWM vs a
traditional 8 bit DAC to control 3 wire fans. (see typical schematic of a 3 wire fan drive in Figure 1-1 by DAC and Figure 1-
2 by PWM).
Note: A typical PC has up to 10 bands (zones) of RPMs that they run the fan in – stepping around mechanical
resonant frequencies of the platform.
FIGURE 1-1: 3-WIRE FAN DRIVE BY DAC
MEC140x/
MEC141x/
MEC142x
Fan
Driver
(e.g.
APL5606)
VFSM
VIN
VSET
DAC
+5V
+3.3V
TACH
2.2uF
VOUT = 1.6 x VSET
2.2uF 1000pF
Fan Connector
10k
0.01uF
3-Wire Fan
Fan Volt
TACH
GND
 2017 Microchip Technology Inc. DS00002137B-page 3
AN2137
FIGURE 1-2: 3-WIRE FAN DRIVE BY PWM WITH R/C FILTER
MEC140x/
MEC141x/
MEC142x
Fan
Driver
(e.g.
APL5606)
VFSM
VIN
VSET
PWM
(1KHz)
TACH
10k
10uF
2.2uF
VOUT = 1.6 x VSET
2.2uF 1000pF
0.01uF
3-Wire Fan
Fan Volt
TACH
GND
+5V
Fan Connector
+3.3V
10k


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Marke: Microchip
Kategorie: Nicht kategorisiert
Modell: MEC1428

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