Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= 3.0V to 5.5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C and V
CC
= 5V.)
PARAMETER
POWER SUPPLY (V
CC
)
Supply Voltage
Supply Current
OUTPUT (OUT)
Output Voltage Range
Output Sink Current
Output Source Current
TACHOMETER INPUTS (TACH_)
Tachometer Threshold
Tachometer Input Impedance
FEEDBACK (FB)
DAC Differential Nonlinearity
Useful DAC Resolution
Feedback Input Impedance
Input Low Voltage
Input High Voltage
Input Hysteresis
Pullup Resistor
Output Sink Current
R
FB
V
IL(GPIO_)
V
IH(GPIO_)
V
HYS
R
GPIO_
I
GPIO_
V
GPIO_
= 0.4V
10
V
CC
≤
3.6V
V
CC
> 3.6V
2
3
200
100
Guaranteed monotonicity on FB (Note 1)
Measured at FB (Note 1)
0 < VFB < 9V
70
100
5
8
150
0.8
LSB
bits
kΩ
V
TACH_
R
TACH_
5V fan, 0 < V
FB
< 4.5V
12V fan, 0 < V
FB
< 9V
0 < V
TACH
< 9V
V
FB
+ 0.5
V
FB
+ 1.0
70
100
V
FB
+1.5
V
FB
+3
150
V
kΩ
V
OUT
I
SINK
I
SOURCE
I
OUT
= ±100µA
V
OUT
= 0.5V
V
OUT
= V
CC
- 1.8V
0.3
10
50
V
CC
- 0.3
V
mA
mA
V
CC
I
CC
Full-on mode, I
OUT
= 0
3.0
5.5
10
V
mA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL-PURPOSE INPUTS/OUTPUTS (GPIO_) (Note 2)
V
V
mV
kΩ
mA
2
Maxim Integrated
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I
2
C-Compatible Interface
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3.0V to 5.5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C and V
CC
= 5V.)
PARAMETER
ADDRESS SELECT (ADD)
ADD Input Low Voltage
ADD Input High Voltage
ADD Input Leakage
ADD External Pulldown Resistor
to GND
ADD Pulldown Current
SMBus/I
2
C INTERFACE (SDA, SCL)
Data Output Sink Current
Input Leakage Current
Input Low Voltage
Input High Voltage
Input Hysteresis
V
IL
V
IH
V
HYS
V
CC
≤
3.6V
V
CC
> 3.6V
2
3
200
I
SDA
V
SDA
= 0.6V
0 < V
IN
< V
CC
6
±1
0.8
mA
µA
V
V
mV
V
IL(ADD)
V
IH(ADD)
I
LADD
R
ADD
I
ADD
Selects slave address 90h (Table 1)
Selects slave address 96h (Table 1)
Selects slave address 36h (Table 1) (Note 3)
Selects slave address 3Eh (Table 1)
V
ADD
= 0.5V (Note 4)
V
CC
- 0.05
-1
9.5
-80
0
10.5
-40
0.1
V
V
µA
kΩ
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
TIMING CHARACTERISTICS
(V
CC
= 3.0V to 5.5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C and V
CC
= 5V.)
PARAMETER
TACHOMETERS
Glitch Rejection
GPIO2
(Note 2)
Clock Frequency
Clock Frequency Uncertainty
f
CLK
f
CLK
V
CC
= 5V
-10
0
1.3
0.6
1.3
0.6
(Note 5)
0
100
(Note 6)
(Note 6)
I
SINK
< 6mA (Note 6)
20 + 0.1C
B
(pF)
20 + 0.1C
B
(pF)
20 + 0.1C
B
(pF)
300
300
250
900
254
+10
400
kHz
%
kHz
µs
µs
µs
µs
µs
ns
ns
ns
ns
Minimum pulse duration
500
µs
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus/I
2
C INTERFACE (Figures 3, 4)
SCL Clock Frequency
f
SCL
Bus Free Time Between Stop
and Start Condition
Hold-Time Start Condition
Low Period of the SCL Clock
High Period of the SCL Clock
Data Hold Time
Data Setup Time
Rise-Time SDA/SCL Signal
(Receiving)
Fall-Time SDA/SCL Signal
(Receiving)
Fall-Time SDA Signal
(Transmitting)
t
BUF
t
HD:STA
t
LOW
t
HIGH
t
HD:DAT
t
SU:DAT
t
R
t
F
t
F
Maxim Integrated
3
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I
2
C-Compatible Interface
TIMING CHARACTERISTICS (continued)
(V
CC
= 3.0V to 5.5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C and V
CC
= 5V.)
PARAMETER
Setup Time for Stop Condition
Pulse Width of Spike Suppressed
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
SYMBOL
t
SU:STO
t
SPIKE
CONDITIONS
MIN
0.6
0
50
TYP
MAX
UNITS
µs
ns
For proper measurement of V
FB
, connect OUT and FB as shown in the
Typical Operating Circuit.
GPIO2, GPIO3, and GPIO4 only in the MAX6651.
Guaranteed by design and not 100% production tested.
For R
ADD
component test purposes only.
Note that the transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCL’s
falling edge.
Note 6:
C
B
is the total capacitance of one bus line in pF. Tested with C
B
= 400pF. Rise and fall times are measured between 0.3 x
V
CC
and 0.7 x V
CC
.
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
INTERNAL OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX6650/51-01
INTERNAL OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX6650/51-02
FEEDBACK VOLTAGE
vs. TEMPERATURE
MAX6650/51-03
265
300
2.5
2.4
FEEDBACK VOLTAGE (V)
2.3
2.2
2.1
2.0
1.9
V
FAN
= 12.0V, V
FAN
= 5.5V
V
CC
= 3.0V
V
CC
= 5.5V,
V
FAN
= 5.5V, V
FAN
= 12.0V
260
FREQUENCY (kHz)
280
FREQUENCY (kHz)
V
CC
= 5.5V
260
255
250
240
V
CC
= 3.0V
245
220
240
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
200
-50
0
50
100
TEMPERATURE (°C)
1.8
-50
0
50
100
TEMPERATURE (°C)
FEEDBACK VOLTAGE vs. SUPPLY
VOLTAGE (DAC SET TO 35)
MAX6650/51-04
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6650/51-05
SUPPLY CURRENT vs. TEMPERATURE
V
CC
= 5.5V
3.5
SUPPLY CURRENT (mA)
MAX6650/51-06
2.20
2.15
FEEDBACK VOLTAGE (V)
2.10
2.05
2.00
1.95
1.90
1.85
1.80
3.0
3.5
4.0
4.5
5.0
V
FAN
= 12.0V
V
FAN
= 5.5V
3.8
3.6
SUPPLY CURRENT (mA)
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
4.0
3.0
2.5
V
CC
= 3V
2.0
1.5
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
SUPPLY VOLTAGE (V)
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
5.5
SUPPLY VOLTAGE (V)
4
Maxim Integrated
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I
2
C-Compatible Interface
Pin Description
PIN
MAX6650
1
—
2
3
4
5
—
6
7
—
8
9
10
PIN
NAME
MAX6651
1
2, 3, 16
4
5
6
8
7, 12
9
10
11
13
14
15
TACH0
TACH2, TACH3,
TACH1
GND
SDA
SCL
ADD
GPIO4, GPIO3
GPIO1
GPIO0
GPIO2
OUT
V
CC
FB
Tachometer Input. Used to close the loop around the tachometer.
Tachometer Inputs. Used to monitor tachometers only.
Ground
2-Wire Serial-Data Input/Output (open drain)
2-Wire Serial Clock Input
Slave Address Select Input (Table 1)
General-Purpose Input/Output (open drain)
General-Purpose Input/Output (open drain). Configurable to act either as an out-
put or as an input (FULL
ON
or general purpose).
General-Purpose Input/Output (open drain). Configurable to act as a general
input/output line or an active-low
ALERT
output.
General-Purpose Input/Output (open drain). Configurable to act as a general
input/output line, an internal clock output, or an external clock input.
Output. Drives the external MOSFET or bipolar transistor.
+3.0V to +5.5V Power Supply
Feedback Input. Closes the loop around the external MOSFET or bipolar tran-
sistor.
FUNCTION
Detailed Description
The MAX6650/MAX6651 use an SMBus/I
2
C-Compatible
interface to regulate and monitor the speed of
5VDC/12VDC brush-less fans with built-in open-collec-
tor/drain tachometers. Regulating fan speed propor-
tionally with temperature saves power, increases fan
life, and reduces acoustic noise. Since fan speed is
proportional to the voltage across the fan, the
MAX6650/MAX6651 control the speed by regulating the
voltage on the low side of the fan with an external MOS-
FET or bipolar transistor.
The MAX6650/MAX6651 each contain two internal con-
trol loops. The first loop controls the voltage across the
fan. The internal digital-to-analog converter (DAC) sets
the reference voltage for an internal amplifier (Figure 1),
which then drives the gate of an external N-channel
MOSFET (or the base of a bipolar transistor) to regulate
the voltage on the low side of the fan. As the reference
voltage provided by the DAC changes, the feedback
amplifier automatically adjusts the feedback voltage,
which changes the voltage across the fan.
Maxim Integrated
The second control loop consists of the internal digital
logic that controls the fan’s speed. The MAX6650/
MAX6651 control fan speed by forcing the tachometer
frequency to equal a reference frequency set by the
Fan-Speed Register, the prescaler, and the internal
oscillator (see the
Fan-Speed Register
section). When
the tachometer frequency is too high, the value of the
DAC’s input register is increased by the regulator.
Once the DAC voltage increases, the analog control
loop forces the feedback voltage to rise, which reduces
the voltage across the fan. Since fan speed is propor-
tional to the voltage across the fan, the fan slows down.
2-Wire SMBus/I
2
C-Compatible
Digital Interface
From a software perspective, the MAX6650/MAX6651
appear as a set of byte-wide registers that contain
speed control, tachometer count, alarm conditions, or
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