EMC2101-R-ACZL-TR datasheet(47/56 Pages) MICROCHIP

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DS20006307A-page 47

EMC2101

APPENDIX B: ADVANCED PWM

OPTIONS

The PWM Frequency Register determines the number

of clocks (set by the CLK_SEL bit or the PWM_D reg-

ister settings) represent 1/2 of the period of the final

PWM output waveform. Therefore, as the PWM Fre-

quency Register is updated, the PWM frequency is like-

wise updated. However, it also directly affects the PWM

Resolution and PWM duty cycle.

The PWM frequency is set according to Equation 3 (A

or B) or, if the PWM Divide Register is used,

Equation 5-4 (see Section 5.20 “PWM Frequency

Divide Register”).

The PWM Frequency Register does not affect the Fan

Setting (either the Fan Setting Register or the Fan Set-

ting entries in the Fan Control Look-up Table Regis-

ters).

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 Fre-

quency Register changes (or the Fan Setting changes)

the effective duty cycle will vary according to

Equation 1 and the PWM resolution will vary according

to Equation 2. This is a result of the “on” time deter-

mined by Fan Setting changing with respect to the

overall PWM period determined by the PWM Fre-

quency Register.

If the Fan Setting is set at a value that is higher than 2x

the PWM Frequency Register settings, the PWM out-

put will be at 100% duty cycle.

Table A.1 shows the effective resolution, duty cycle,

and frequency as the PWM Frequency Register setting

is changed.

EQUATION 1:

EQUATION 2:

EQUATION 3:

EFFECTIVE_DUTY_CYCLE

FAN_SETTING

PWM_F 2



------------------------------------------



 100



Where:

PWM_F

The setting of the PWM Frequency

EFFECTIVE_RESOLUTION

100%

PWM_F 2



-------------------------------

Where:

PWM_F

The setting of the PWM Frequency

PWM_FREQUENCY

360k

2PWM_F



-------------------------------

Where:

PWM_F

The setting of the PWM Frequency

Divide Register (4Eh)

CLK_SEL = ‘0’

CLK_SEL = ‘1’

(A)

(B)

PWM_FREQUENCY

1.4k

2PWM_F



-------------------------------

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