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| U6083B Datasheet, PDF (5/12 Pages) TEMIC Semiconductors – PWM Power Control with Interference Suppression | |||
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Example for Oscillator
Frequency Calculation
Calculation Example
Oscillator Frequency
U6083B
Switching thresholds
VT100
VT100
VT<100
VT<100
VTL
VTL
where
= High switching threshold (100% duty cycle)
= VS ´ a1 = (VBatt - IS ´ R3) ´ a1
= High switching threshold (< 100% duty cycle)
= VS ´ a2 = (VBatt - IS ´ R3) ´ a2
= Low switching threshold
= VS ´ a3 = (VBatt - IS ´ R3) ´ a3
a1, a2 and a3 are fixed values
The above mentioned threshold voltages are calculated for the following values given in
the data sheet.
VBatt
VT100
VT<100
VTL
= 12 V, IS = 4 mA, R3 = 150 W, a1 = 0.7, a2 = 0.67 and a3 = 0.28
= (12 V - 4 mA ´ 150 W) ´ 0.7 » 8 V
= 11.4 V ´ 0.67 = 7.6 V
= 11.4 V ´ 0.28 = 3.2 V
3 cases have to be distinguished
1. f1 for duty cycle = 100%, no slope reduction with capacitor C4
(see Figure 4 on page 10)
f1 = -2----´-----(---V----T---1--0--I-0-O---âS----C-V----T---L---)---´-----C----2- , where C2 = 68 nF, IOSC = 45 µA
f1 = ... = 75 Hz
2. f2 for duty cycle < 100%, no slope reduction with capacitor C4
For a duty cycle of less than 100%, the oscillator frequency, f, is as follows:
f2
=
-------------------------I--O----S---C-------------------------- ,
2 ´ (VT<100 â VTL) ´ C2
where
C2
=
68
nF,
IOSC =
45
µA
f2 = ... = 69 Hz
3. f3 with duty cycle < 100% with slope reduction capacitor C4 (see âOutput Slope
Controlâ on page 6)
f3 = 2-----´-----(---V----T---<--1---0---0----â----V----T---L--I-)o---s-´-c----C----2----+-----2----V----B---a--t--t---´----C-----4-
where C2 = 68 nF, IOSC = 45 µA, C4 = 1.8 nF
f3 = ... = 70 Hz
By selecting different values of C2 and C4, it is possible to have a range of oscillator fre-
quencies from 10 to 2000 Hz as shown in the data sheet.
5
4770AâAUTOâ11/03
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