EMC6D102 SMSC Corporation, EMC6D102 Datasheet - Page 36

• Manufacturer Part Number: EMC6D102
• Description: Fan Control Device
• Manufacturer: SMSC Corporation

Revision 0.4 (06-15-06)
RRX-
[2:0]
110
111
Ramping Duty Cycle
Calculate Duty Cycle
PWM Duty Cycle
Ramping Duty Cycle
Calculate Duty Cycle
PWM Duty Cycle
Example 1: PWM period < Ramp Rate Step Size
PWM frequency = 87.7Hz (11.4msec) & PWM Ramp Rate = 38.46Hz (26msec)
Example 2: PWM period > Ramp Rate Step Size
PWM frequency = 11Hz (90.9msec) & PWM Ramp Rate = 38.46Hz (26msec)
Notes:
It should be noted that the actual duty cycle on the pin is created by the PWM Ramp Rate Control
block and latched on the rising edge of the PWM output. Therefore, the current PWM duty cycle may
lag the PWM Calculated Duty Cycle.
PWM RAMP TIME (SEC)
100% DUTY CYCLE)
The PWM Duty Cycle latches the Ramping Duty Cycle on the rising edge of the PWM output.
The calculated duty cycle, ramping duty cycle, and the PWM output duty cycle are asynchronous
to each other, but are all synchronized to the internal 90kHz clock source.
(TIME FROM 33%
DUTY CYCLE TO
1.6
0.8
70h
70h
70h
70h
70h
Figure 6.4 Illustration of PWM Ramp Rate Control
70h
Table 6.1 PWM Ramp Rate (continued)
11.4ms
71h
Fan Control Device with Hardware Monitoring and Acoustic Noise Reduction Features
71h
PWM RAMP TIME (SEC)
71h
CYCLE TO 100% DUTY
26ms
(TIME FROM 0% DUTY
26ms
71h
DATASHEET
11.4ms
CYCLE)
71h
1.275
2.55
74h
74h
36
11.4ms
72h
72h
72h
26ms
26ms
71h
90.9msec
11.4ms
72h
11.4ms
73h
(PWM STEP SIZE =
PWM STEP
73h
73h
TIME PER
11.4ms
73h
10 msec
5 msec
1/255)
11.4ms
73h
11.4ms
74h
74h
74h
SMSC EMC6D102
74h
11.4ms
74h
RAMP
RATE
PWM
(HZ)
100
200
Datasheet
74h