emc2101 Standard Microsystems Corp., emc2101 Datasheet - Page 48

• Manufacturer Part Number: emc2101
• Description: Emc2101 Fan Control With 1?c Accurate Temperature Monitoring
• Manufacturer: Standard Microsystems Corp.

Appendix A Advanced PWM Options
APPLICATION NOTE: If the Fan Setting is set at a value that is higher than 2x the PWM Frequency Register
Revision 2.53 (02-19-08)
EFFECTIVE_DUTY_CYCLE
EFFECTIVE_RESOLUTION
The PWM Frequency Register determines the number of clocks (set by the CLK_SEL bit or the
PWM_D register settings) represent 1/2 of the period of the final PWM output waveform. Therefore,
as the PWM Frequency Register is updated, the PWM frequency is likewise updated. However, it also
directly affects the PWM Resolution and PWM duty cycle.
The PWM frequency is set according to
used,
The PWM Frequency Register does not affect the Fan Setting (either the Fan Setting Register or the
Fan Setting entries in the Fan Control Look-up Table Registers).
The Fan Setting Register determines the number of clocks that the PWM output is high for is always
based on 64 time steps for a PWM cycle. As the PWM Frequency Register changes (or the Fan Setting
changes) the effective duty cycle will vary according to
according to
respect to the overall PWM period determined by the PWM Frequency Register.
Table 6.34
setting is changed.
PWM_FREQUENCY
PWM_FREQUENCY
Equation
settings, the PWM output will be at 100% duty cycle.
shows the effective resolution, duty cycle, and frequency as the PWM Frequency Register
Equation
[5].
=
⎛
⎝
FAN_SETTING
--------------------------------------------
[7]. This is a result of the “on” time determined by Fan Setting changing with
PWM_F 2
=
=
=
-----------------------------
2xPWM_F
-----------------------------
2xPWM_F
------------------------------- -
PWM_F 2
360k
1.4k
100%
×
DATASHEET
×
⎞
⎠
×
Equation [8]
100%
48
SMBus Fan Control with 1°C Accurate Temperature Monitoring
Where: PWM_F is the setting of the PWM
Where: PWM_F is the setting of the PWM
or
Equation [6]
Equation [9]
Where: PWM_F is the setting of the
PWM_D is the setting of the PWM
Frequency Divide Register (4Eh)
Frequency Register (4Dh)
Frequency Register (4Dh)
PWM Frequency register (4Dh)
CLK_SEL = ‘0’
CLK_SEL = ‘1’
and the PWM resolution will vary
or, if the PWM Divide Register is
SMSC EMC2101
Datasheet
[6]
[7]
[8]
[9]