MAX6660EVKIT Maxim Integrated Products, MAX6660EVKIT Datasheet - Page 18

• Manufacturer Part Number: MAX6660EVKIT
• Description: EVAL KIT FOR MAX6660
• Manufacturer: Maxim Integrated Products

Specifications of MAX6660EVKIT

• Sensor Type: Temperature, Fan Controller
• Sensing Range: -40°C ~ 125°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1°C
• Voltage - Supply: 3 V ~ 5.5 V
• Embedded: No
• Utilized Ic / Part: MAX6660
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The FCR register (Table 8) programs the fan’s update
time interval in free-running autonomous mode (RUN/
STOP = 0). The conversion rate byte’s POR state is 02h
(0.25Hz). The MAX6660 uses only the 3LSBs of this
register. The 4MSBs are “don’t cares.” The update rate
tolerance is ±25% (max) at any rate setting.
In the thermal open loop but fan closed-loop mode, the
feedback loop can be broken and the temperature data
read directly. After performing external manipulations,
the result can be injected back into the fan control loop
by writing to the FSC register to control fan speed. Fan
closed-loop mode is selected by setting bit 0 of the FG
to zero.
In fan control open-loop mode, selected by setting bit 0
of the FG register to 1, the gain block is bypassed and
the FSC register is used to program the fan voltage
rather than the fan speed. In the fan open-loop mode,
both the temperature feedback loop and fan-speed
control loop are broken, which results in the TACH IN
input becoming disabled. A direct voltage can be
applied after reading the temperature, using the FSC
register, to the fan that provides more flexibility in exter-
nal control algorithms. By selecting fan open-loop
mode, the MAX6660 automatically invokes thermal
open-loop mode.
The fan driver consists of an amplifier and low-side
NMOS device whose drain is connected to FAN and is
the input from the low side of the fan. The FET has a
typical 4Ω on-resistance with a typical 320mA maxi-
mum current limit. The driver has a thermal shutdown
sensor that senses the driver’s temperature. It shuts
down the driver if the temperature exceeds +150°C.
The driver is reactivated once the temperature has
dropped below +140°C.
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Table 13. Fan Tachometer Count Limit (RFTCL/WFTCL)
18
Note: The Fan Limit register is programmed with the maximum speed that is compared against the value in the FS register (Address
COMMAND
POR STATE
REGISTER/
ADDRESS
______________________________________________________________________________________
17) to produce an error output to the Status register.
BIT
Fan Conversion Rate Byte
(MSB)
7
1
Fan Closed Loop
Fan Open Loop
6
1
Fan Driver
READ LIMIT/FAILURE REGISTER
5
1
FL (18h = READ, 1Ch = WRITE)
The TACH IN input connects directly to the tachometer
output of a fan. Most commercially available fans have
two tachometer pulses per revolution. The tachometer
input is fully compatible with tachometer signals, which
are pulled up to V
When a fan does not come equipped with a tachometer
output, the MAX6660 uses commutating generated cur-
rent pulses for speed detection. This mode is entered
by setting the FG register’s bit 1 to 1. An internal cur-
rent pulse is generated whenever a step increase
occurs in the fan current. Connecting an external resis-
tor between the GAIN pin and V
sitivity of current pulses to changes in fan current. In
general, the lower the resistor value, then the lower the
sensitivity, and the fan is easier to turn ON and can use
a smaller external capacitor across its terminals. A suit-
able resistor range is 1kΩ to 5kΩ.
The MAX6660 detects fan failure by comparing the
value in the Fan Tachometer Count (FTC) register, a
READ ONLY register, with a limit stored in the Fan
Tachometer Count Limit (FTCL) register (Table 13). A
counter counts the number of on-chip oscillator pulses
between successive tachometer pulses and loads the
FTC register every time a tachometer pulse arrives. If
the value in FTC is greater than the value in FTCL, a
failure is indicated. In fan closed loop, a flag is activat-
ed when the fan is at full speed.
Set the Fan Tachometer Limit Byte to:
where N = fan fail ratio and f = frequency of fan
tachometer.
The factor N is less than 1 and produces a fan failure
indication when the fan should be running at full speed
but is only reaching a factor N of its expected frequen-
cy. The factor N is typically set to 0.75 for all fan
4
1
3
1
VFAN
Commutating Current Pulses
f
L
= 8415/[N
.
Fan-Failure Detection
2
1
CC
✕
f]
can reduce the sen-
1
1
TACH IN
0
1