MAX6643LBBAEE+ Maxim Integrated Products, MAX6643LBBAEE+ Datasheet - Page 6

• Manufacturer Part Number: MAX6643LBBAEE+
• Description: IC CNTRLR FAN SPEED 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6643LBBAEE+

• Function: Fan Control, Temp Monitor
• Topology: ADC, PWM Generator, Tach Counter
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: PWM
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Full Temp Accuracy: +/- 3.5 C, +/- 3 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

There are two options for the behavior of the PWM out-
puts at power-up. Option 1 (minimum duty cycle = 0):
at power-up, the PWM duty cycle is zero. Option 2
(minimum duty cycle = the start duty cycle): at power-
up, there is a startup delay, after which the duty cycle
goes to 100% for the spin-up period. After the startup
delay and spin-up, the duty cycle drops to its minimum
value. The minimum duty cycle is in the 0% to 50%
range (see the Selector Guide).
To control fan speed based on temperature, T
set to the temperature beyond which the fan should spin
at 100%. T
the duty cycle can be reduced to its minimum value.
After power-up and spin-up (if applicable), the duty
cycle reduces to its minimum value (either 0% or the
start duty cycle). For option 1 (minimum duty cycle = 0),
if the measured temperature remains below T
duty cycle remains at zero (see Figure 1). If the temper-
ature increases above T
100% for the spin-up period, and then goes to the start
duty cycle (for example, 40%). If the measured temper-
ature remains above T
measured (4s later), the duty cycle begins to increase,
incrementing by 1.5% every 4s until the fan is spinning
fast enough to reduce the temperature below T
For option 2 (minimum duty cycle = start duty cycle), if
the measured temperature remains below T
duty cycle does not increase and the fan continues to
run at a slow speed. If the temperature increases
above T
menting by 1.5% every 4s until the fan is spinning fast
enough to reduce the temperature below T
Figure 2). In both cases, if only a small amount of extra
cooling is necessary to reduce the temperature below
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Table 2. Setting T
(MAX6643 and MAX6644)
High-Z = High impedance.
6
_______________________________________________________________________________________
High-Z
High-Z
High-Z
TL2
HIGH
0
0
0
1
1
1
LOW
, the duty cycle begins to increase, incre-
is set to the temperature below which
LOW
HIGH
High-Z
High-Z
High-Z
HIGH
TL1
0
1
0
1
0
1
when temperature is next
, the duty cycle goes to
T
L SUFFIX
LOW
HIGH
15
20
25
30
35
40
45
50
55
HIGH
HIGH
HIGH
(°C)
HIGH
, the
, the
.
(see
is
Figure 1. Temperature-Controlled Duty-Cycle Change with
Minimum Duty Cycle 30%
Figure 2. Temperature-Controlled Duty-Cycle Change with
Minimum Duty Cycle 30%
STARTUP
STARTUP
MAX664_B HAS 30% PWM_OUT DUTY CYCLE DURING STARTUP.
SPIN-UP
SPIN-UP
TIME
TIME
TIME
TIME
T
T
T
T
HIGH
LOW
HIGH
LOW