Electronic Components Datasheet Search |
|
MAX6639ATE Datasheet(PDF) 9 Page - Maxim Integrated Products |
|
MAX6639ATE Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 22 page FANFAIL The FANFAIL output asserts to indicate that one of the fans has failed or is spinning slower than the required speed. The MAX6639 detects fan fault depending on the fan-control mode. In PWM mode, the MAX6639 pro- duces a square wave with a duty cycle set by the value written to the duty-cycle registers (26h and 27h). In this mode, the MAX6639 signals a fan fault when the tachometer count is greater than the maximum tachome- ter count value stored in the appropriate register (22h and 23h). After the MAX6639 asserts FANFAIL, the fan with a tachometer fault goes to full speed for 2s in an attempt to restart the fan and then returns to the original duty-cycle settings. Reading the status register clears the FANFAIL status bits and the output. The MAX6639 measures the fan speed again after 2s. The MAX6639 asserts FANFAIL if it detects the fan fault again. In RPM mode (either automatic or manual), the MAX6639 checks for fan failure only when the duty cycle reaches 100%. It asserts FANFAIL when the tachometer count is greater than twice the target tachometer count. In manual RPM mode, registers 22h and 23h store the target tachometer count value. In automatic RPM mode, these registers store the maxi- mum tachometer count. Fan-Speed Control The MAX6639 adjusts fan speed by controlling the duty cycle of a PWM signal. This PWM signal then either modulates the DC brushless fan’s power supply or dri- ves a speed-control input on a fan that is equipped with one. There are three speed-control modes: PWM, in which the PWM duty cycle is directly programmed over the SMBus; manual RPM, in which the desired tachometer count is programmed into a register and the MAX6639 adjusts its duty cycle to achieve the desired tachometer count; and automatic RPM, in which the tachometer count is adjusted based on a programmed temperature profile. The MAX6639 divides each PWM cycle into 120 time slots. Registers 26h and 27h contain the current values of the duty cycles for PWM1 and PWM2, expressed as the effective time-slot length. For example, the PWM1 output duty cycle is 25% when register 26h reads 1Eh (30/120). PWM Control Mode Enter PWM mode by setting bit 7 of the fan 1 or 2 con- figuration 1 register (10h and 14h) to 1. In PWM control mode, the MAX6639 generates PWM signals whose duty cycles are specified by writing the desired values to fan duty-cycle registers 26h and 27h. When a new duty-cycle value is written into one of the fan duty-cycle registers, the duty cycle changes to the new value at a rate determined by the rate-of-change bits [6:4] in the fan 1 or 2 configuration 1 register. The rate-of-change of the duty cycle ranges from 000 (immediately changes to the new programmed value) to 111 (changes by 1/120 every 4s). See Table 5 and the Fan 1 and 2 Configuration 1 (10h and 14h) section. Manual RPM Control Mode Enter manual RPM control mode by setting bits 2, 3, and 7 of the fan 1 or 2 configuration 1 register (10h and 14h) to zero. In the manual RPM control mode, the MAX6639 adjusts the duty cycle and measures the fan speed. Enter the target tachometer count in register 22h for fan 1 and register 23h for fan 2. The MAX6639 compares the target tachometer count with the mea- sured tachometer count and adjusts the duty cycle so that the fan speed gradually approaches the target tachometer count. The first time manual RPM control mode is entered, the initial PWM duty cycle is determined by the target tachometer count: where targetTACH is the value of the target tachometer count in the target tach count register (22h or 23h). If the initial duty-cycle value is over 120, the duty cycle is 100%. If spin-up is enabled (bit 7 in registers 13h and 17h) and the fan is not already spinning, the duty cycle first goes to 100% and then goes to the initial duty-cycle value. Every 2s, the MAX6639 counts the fan’s period by counting the number of pulses stored in registers 24h and 25h. If the count is different from the target count, the duty cycle is adjusted. If a nonzero rate-of-change is selected, the duty cycle changes at the specified rate until the tachometer count is within ±5 of the target. Then the MAX6639 gets into a locked state and updates the duty cycle every 2s. Automatic RPM Control Mode In the automatic RPM control mode, the MAX6639 mea- sures temperature, sets a target tachometer count based on the measured temperature, and then adjusts the duty cycle so the fan spins at the desired speed. Enter this mode by setting bit 7 of the fan 1 or 2 config- uration 1 register (10h and 14h) to zero and selecting the temperature channel that controls the fan speed using bits 2 and 3 of the configuration register. In both RPM modes (automatic and manual), the MAX6639 implements a low limit for the tachometer Initial duty cycle t etTACH arg = − 255 2 2-Channel Temperature Monitor with Dual, Automatic, PWM Fan-Speed Controller _______________________________________________________________________________________ 9 |
Similar Part No. - MAX6639ATE |
|
Similar Description - MAX6639ATE |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |