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PDF MAX31790 Data sheet ( Hoja de datos )
| Número de pieza | MAX31790 | |
| Descripción | 6-Channel PWM-Output Fan RPM Controller | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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MAX31790
EVALUATION KIT AVAILABLE
6-Channel PWM-Output Fan RPM Controller
General Description
The MAX31790 controls the speeds of up to six fans
using six independent PWM outputs. The desired fan
speeds (or PWM duty cycles) are written through the I2C
interface. The outputs drive “4-wire” fans directly, or can
be used to modulate the fan’s power terminals using an
external pass transistor.
Tachometer inputs monitor fan tachometer logic outputs
for precise (Q1%) monitoring and control of fan RPM as
well as detection of fan failure. Six pins are dedicated
tachometer inputs. Any of the six PWM outputs can also
be configured to serve as tachometer inputs.
The PWM_START inputs select the PWM output status
at startup to ensure appropriate fan drive when power is
first applied.
To ensure low acoustic impact of fan control, all changes
in PWM duty cycle take place at a controlled, program-
mable rate.
The MAX31790’s 3.0V to 5.5V supply voltage range and
I2C-compatible interface make it ideal for fan control in
a wide range of cooling applications. The MAX31790 is
available in a 28-pin TQFN package and operates over
the -40NC to +125NC temperature range.
Benefits and Features
●● Provides Precise Fan Control and Monitoring for
Large Fan Count Applications
• Controls Up to Six Independent Fans with PWM
Drive
• Up to 12 Tachometer Inputs
• Controlled Duty Cycle Rate-of-Change for Best
Acoustics
●● Improves System Reliability
• Versatile Startup Configurations Provide Reliable
Fan Control at Power-up without Having to Wait for
System µC Direction
• I2C Bus Interface with Timeout and Watchdog
Applications
●● Servers
●● Networking
●● Telecom
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part,
refer to: www.maximintegrated.com/MAX31790.related
Typical Operating Circuit
HOST
INTERFACE
SET
POWER-UP
VALUES
CRYSTAL
(OPTIONAL)
VCC
3.0V TO 5.5V
VCC 12pF
RPU
SDA
SCL
FAN_FAIL
FULL_SPEED
XTAL1 XTAL2
12pF
VCC
MAX31790
0.1µF
VCC
PWMOUT1
TACH1
PWMOUT2
V4-WIRE FAN
FAN1
CLKOUT
PWM_START1
PWM_START0
FREQ_START
SPIN_START
WD_START
ADD1
ADD0
I2C INTERFACE,
REGISTERS,
AND
CONTROL LOGIC
TACH2
PWMOUT3
PWM OUTPUT
DRIVER,
TACH MONITOR
TACH3
PWMOUT4
TACH4
PWMOUT5
TACH5
PWMOUT6
TACH6
GND 6 CHANNELS
19-6540; Rev 2; 1/15
1 page  
MAX31790
6-Channel PWM-Output Fan RPM Controller
SDA
tBUF
SCL
tLOW
tHD:STA
STOP START
tR
tHD:DAT
NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN).
Figure 1. I2C Timing Diagram
tF
tHIGH
tSU:DAT
tHD:STA
tSU:STA
REPEATED
START
tSP
tSU:STO
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
POWER-SUPPLY CURRENT
vs. POWER-SUPPLY VOLTAGE
4
3
PWM FREQUENCY = 25kHz 1.47kHz
2
1
PWM FREQUENCY = 25Hz
0
2.5 3.5 4.5 5.5 6.5
SUPPLY VOLTAGE (V)
POWER-SUPPLY CURRENT
vs. TEMPERATURE
4
VDD = 3.3V
3
2 PWM FREQUENCY = 25kHz
1
0
-50
PWM FREQUENCY = 25Hz
0 50 100
TEMPERATURE(°C)
150
www.maximintegrated.com
Maxim Integrated │ 5
5 Page 
MAX31790
6-Channel PWM-Output Fan RPM Controller
Fan Monitoring
Monitoring Tachometer Signals
The TACH inputs accept either tachometer or “locked
rotor” output signals from 3-wire or 4-wire fans. When
measuring fan speed, the device counts the number of
internal 8192Hz (fTOSC/4)clock cycles that occur during
1, 2, 4, 8, 16, or 32 tachometer periods. (The speed of
each fan is measured once per second.) The number of
tachometer periods is selectable for each fan by using
the appropriate Fan Dynamics register. Tachometer
pulses less than tTACHMIN in duration are ignored to
minimize the effect of noise on the tachometer lines. The
TACH count for a given RPM can be obtained from the
following equation:
where:
TACH C=ount
NP
60
× RPM
×
SR
×
8192
NP = number of tachometer pulses per revolution.
Most general-purpose brushless DC fans produce two
tachometer pulses per revolution.
SR = 1, 2, 4, 8, 16, or 32. This is the number of tachom-
eter periods over which the tachometer clock is counted.
See the Speed Range bit information described in the
corresponding Fan Dynamics register description.
The tachometer count consists of 11 bits in the TACH
Count registers and is available in RPM and PWM
modes. In RPM mode, the desired fan count is written
to the associated TACH Target Count register. In PWM
mode, the desired fan duty cycle is written to the associ-
ated PWMOUT Target Duty Cycle register.
Note that the device is intended to be used with 4-wire
fans. Modulating a fan’s power supply with a PWM
waveform, as is sometimes done with 2-wire and 3-wire
fans, results in incorrect tachometer counts due to the
periodic removal of power from the fan’s internal circuitry.
Therefore, it is suggested to use PWM mode when inter-
facing with 2-wire or 3-wire fans.
Using PWM Outputs as Tachometer Inputs
Each Fan Configuration register includes a PWM/TACH
bit that allows the PWMOUT to be configured as a TACH
input. In TACH mode, the settings for TACH input enable,
locked rotor operation, and TACH pulses counted that
have been selected for a given fan channel apply to that
channel’s TACH input and also to TACH signals sensed
by that channel’s PWM output.
Figure 2 to Figure 6 show some examples of TACH-PWM
connections for various fan configurations
TACH1
PWMOUT1 (TACH7)
MAX31790
TACH2
PWMOUT2 (TACH8)
TACH3
PWMOUT3 (TACH9)
TACH4
PWMOUT4 (TACH10)
TACH5
PWMOUT5 (TACH11)
TACH6
PWMOUT6 (TACH12)
Figure 2. 12 Fans, 12 TACH Monitors, No PWM
www.maximintegrated.com
Maxim Integrated │ 11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet MAX31790.PDF ] | |
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