MAX6650 is a linear fan controller. The rotational speed of a 4-wire fan is usually controlled by PWM. MAX6650 cannot provide PWM output, thus MAX6650 is generally not used for a 4-wire fan.
MAX6650
Production
The MAX6650/MAX6651 fan controllers use an SMBus/I²C-compatible interface to regulate and monitor the speed of 5VDC/12VDC brushless fans with built-in...
Datasheet
MAX6650 on Analog.com
MAX6650 is a linear fan controller. The rotational speed of a 4-wire fan is usually controlled by PWM. MAX6650 cannot provide PWM output, thus MAX6650 is generally not used for a 4-wire fan.