LTC6992HS6-2 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
LTC6992HS6-2 Datasheet PDF : 34 Pages
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LTC6992-1/LTC6992-2/
LTC6992-3/LTC6992-4
OPERATION
Pulse Width (Duty Cycle) Modulation
The MOD pin is a high impedance analog input providing
direct control of the output duty cycle. The duty cycle is
proportional to the voltage applied to the MOD pin, VMOD.
Duty Cycle = D =
VMOD
1
−
0.8 • VSET 8
The PWM duty cycle accuracy ΔD specifies that the above
equation is valid to within ±4.5% for VMOD between 0.2 •
VSET and 0.8 • VSET (12.5% to 87.5% duty cycle).
Since VSET = 1V ±30mV, the duty cycle equation may be
approximated by the following equation.
Duty Cycle = D ≅ VMOD − 100mV
800mV
The VMOD control range is approximately 0.1V to 0.9V.
Driving VMOD beyond that range (towards GND or V+) will
have no further affect on the duty cycle.
Duty Cycle Limits
The only difference between the four versions of the
LTC6992 is the limits, or clamps, placed on the output
duty cycle. The LTC6992-1 generates output duty cycles
ranging from 0% to 100%. At 0% or 100% the output
will stop oscillating and rest at GND or V+, respectively.
The LTC6992-2 will never stop oscillating, regardless of
the VMOD level. Internal clamping circuits limit its duty
cycle to a 5% to 95% range (1% to 99% guaranteed).
Therefore, its VMOD control range is 0.14 • VSET to 0.86 •
VSET (approximately 0.14V to 0.86V).
The LTC6992-3 and LTC6992-4 complete the family by
providing one-sided clamping. The LTC6992-3 allows 0%
to 95% duty cycle, and the LTC6992-4 allows 5% to 100%
duty cycle.
Output Polarity (POL Bit)
The duty cycle equation describes a proportional transfer
function, where duty cycle increases as VMOD increases.
The LTC6992 includes a POL bit (determined by the
DIVCODE as described earlier) that inverts the output
signal. This makes the duty cycle gain negative, reducing
duty cycle as VMOD increases.
POL = 0
OUT
POL = 1
OUT
D • tOUT
D = VMOD − 1
0.8 • VSET 8
tOUT
D • tOUT
D
=
1−
VM O D
0.8 • VSET
−
1
8
tOUT
6992 F03
Figure 3. POL Bit Functionality
For more information www.analog.com
Rev. D
17
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