UCC28500-12 Datasheet, PDF (26/35 Pages) Texas Instruments – BiCMOS PFC/PWM COMBINATION CONTROLLER

UCC28500, UCC28501, UCC28502, UCC28503
UCC38500, UCC38501, UCC38502, UCC38503
SLUS419C − AUGUST 1999 − REVISED NOVEMBER 2001
23 dB. Therefore the compensation circuitry needs to have a gain of −23 dB at the desired crossover frequency.
For this example R35 is calculated at approximately 18.2 kΩ. Capacitor C14 is estimated to be approximately
10 nF and C15 is calculated at approximately 180 pF.
ƪ ƫ H(s) + 20 log
V_REF
V_OUT
(46)
R35 + R31 10^{ǒ*GCO(s) dB)GOPTO(s) dB)H(s) dBǓ}
(47)
C14 + _ǒ2p
1
R35
f_C^Ǔ
(48)
ǒ Ǔ ^{C15 +}
1
2p
R35
f_SW
2
(49)
Figure 16 shows the frequency response of the compensation network G_C(s) and Figure 17 shows the
measured frequency response of the loop gain T(s). The frequency response characteristics in Figure 17 show
that f_C is approximately 1.5 kHz with a phase margin of about 55 degrees. The gain margin is approximately
50 dB.
FEEDBACK CONTROL TRANSFER FUNCTION
(GAIN AND PHASE)
vs.
FREQUENCY
60
180
COMPENSATION
PHASE
40
120
20
60
0
COMPENSATION
−20
GAIN
−40
−60
100
1k
10 k
f − Frequency − Hz
Figure 16
0
−60
−120
−180
100 k
TOTAL LOOP TRANSFER FUNCTION
(GAIN AND PHASE)
vs.
FREQUENCY
60
180
40
LOOP PHASE
120
20
60
0
0
−20
LOOP GAIN
−40
−60
−120
−60
100
1k
10 k
f − Frequency − Hz
Figure 17
−180
100 k
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