MAX6645 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX6645 Datasheet PDF : 17 Pages
| |||
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
Table 2. Setting TLOW
(MAX6643 and MAX6644)
TL2
TL1
0
0
0
High-Z
0
1
High-Z
0
High-Z
High-Z
High-Z
1
1
0
1
High-Z
1
1
High-Z = High impedance.
TLOW (°C)
L SUFFIX
15
20
25
30
35
40
45
50
55
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, THIGH is
set to the temperature beyond which the fan should spin
at 100%. TLOW is set to the temperature below which
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 THIGH, the
duty cycle remains at zero (see Figure 1). If the temper-
ature increases above THIGH, the duty cycle goes to
100% for the spin-up period, and then goes to the start
duty cycle (for example, 40%). If the measured temper-
ature remains above THIGH when temperature is next
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 THIGH.
For option 2 (minimum duty cycle = start duty cycle), if
the measured temperature remains below THIGH, the
duty cycle does not increase and the fan continues to
run at a slow speed. If the temperature increases
above THIGH, the duty cycle begins to increase, incre-
menting by 1.5% every 4s until the fan is spinning fast
enough to reduce the temperature below THIGH (see
Figure 2). In both cases, if only a small amount of extra
cooling is necessary to reduce the temperature below
SPIN-UP
TIME
STARTUP
THIGH
TLOW
TIME
Figure 1. Temperature-Controlled Duty-Cycle Change with
Minimum Duty Cycle 30%
SPIN-UP
TIME
STARTUP
MAX664_B HAS 30% PWM_OUT DUTY CYCLE DURING STARTUP.
THIGH
TLOW
TIME
Figure 2. Temperature-Controlled Duty-Cycle Change with
Minimum Duty Cycle 30%
6 _______________________________________________________________________________________
Share Link: 