ISL6731A Datasheet, PDF (18/20 Pages) Intersil Corporation – Power Factor Correction Controllers

ISL6731A, ISL6731B
The output feedback resistor divider gain, G_DIV is:
G_DIV= _V-^V----_OR----^EU----^FT--
(EQ. 77)
The compensation gain uses external impedance networks as
shown in Figure 18, Z_COMP(s) is given by:
Z_COMPs= _---_C-----_v---_c----+----¹-_C----_v---_p----_---_---_s-  -_R---------v------_cC--^R------_--_vv------_cc-_C-------+^--_v------_c--^CC------_--^v-_v-----^c-_pC-------^--_v------_p--^s----_^+----_s-¹----+----₁--
(EQ. 78)
The targeted crossover frequency, F_CV is 7.5Hz. The high
frequency pole, F_PV, is required in order to reject the 2 time line
frequency component. F_PV = 20Hz. The targeted phase margin
is 50°.
60
F_ZV
40
20
F_PV
GmV*Z_COMP (s)
F_CV
Gps (s)
Choose components from the standard values. We have
C_VP = 150nF, C_VC = 1µF, R_VC = 62kΩ. The actual bode plot is
shown in Figure 20.
40
F_CV
120Hz
20
0
0
-20
90
F_CV
60
30
120Hz
60
45
0
-20
-40
G_DIV
G_VLOOP (s)
01
10
100
1k
FREQUENCY (Hz)
FIGURE 20. BODE PLOT OF THE ACTUAL VOLTAGE LOOP GAIN
-60 ₁
10
100
1k
FREQUENCY (Hz)
FIGURE 19. ASYMPTOTIC BODE PLOT OF VOLTAGE LOOP GAIN
The zero, F_Zv is calculated:
F_Zv = -_t--_a---_n----_--_-----_m------+-----_a----_t-_a-^F---_n-^C---_-^V-_F----_C----_V-----_---_--_F----_P----_V----_--_---_
(EQ. 79)
F_Zv = -_t--_a---_n----_--₅----₀----_d---_e----_g-----+-----_a----_t-_a-⁷---_n.--⁵--_--^H_--₇---^z-_.-₅----_H-----_z---_----_--_---₂---₀----_H-----_z---_---_---_ = 2.648Hz
(EQ. 80)
Then the total capacitance used for compensation is calculated:
C_vc + C_vp = --^G-----^P----^S----^--ⁱ---^----^---²----^---_^F---₂-^C--_--^V--_F--^--_C-^---_V--^--_--^G-----^D----^I--^V-----^----^G-----^m------^v- 
^---FF^----_CC^----_VV^-----^---FF^---_P^{-Z---VV------2-2----++-----11--}
(EQ. 81)
Thus, the total compensation capacitance is:
C_vc + C_vp = 1127nF
C_vp = 1127nF  _F-^F---_P-^Z---^VV-- = 149nF
C_vc = 1127nF – 149.1nF = 977nF
R_vc = -₂----_---_-----_---_F----_Z-¹---_V-----_---_C----_V----_C-- = 61.5k
(EQ. 82)
(EQ. 83)
(EQ. 84)
(EQ. 85)
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FN8582.1
February 13, 2015