Datasheet

LT8582
29
8582f
The current mode zero (Z3) is a right half plane zero
which can be an issue in feedback control design, but is
manageable with proper external component selection.
Using the circuit in Figure 17 as an example, Table 8 shows
the parameters used to generate the bode plot shown in
Figure 16.
Table 8. Bode Plot Parameters
PARAMETER VALUE UNITS COMMENT
R
L
20  Application Specific
C
OUT
22 F Application Specific
R
ESR
1 m Application Specific
R
O
305 k Not Adjustable
C
C
4700 pF Adjustable
C
F
47 pF Optional/Adjustable
C
PL
0 pF Optional/Adjustable
R
C
6.49 k Adjustable
R1 130 k Adjustable
R2 14.5 k Not Adjustable
V
REF
1.204 V Not Adjustable
V
OUT
12 V Application Specific
V
IN
5 V Application Specific
g
ma
270 mho Not Adjustable
g
mp
15.1 mho Not Adjustable
L 4.7 H Application Specific
f
OSC
1.5 MHz Adjustable
From Figure 16, the phase is –130° when the gain reaches
0dB, giving a phase margin of 50°. The crossover frequency
is 5kHz, which is many times lower than the frequency of
the RHP zero Z3, thus providing for adequate phase margin.
APPENDIX
Figure 16. Bode Plot for Example Boost Converter
Figure 17. 5V to 12V Boost Converter
FREQUENCY (Hz)
10
–20
GAIN (dB)
PHASE (DEG)
0
100
80
60
40
120
1k
10k
8582 F16
20
100
100k
1M
140
–360
–315
–90
–135
–180
–225
–45
–270
0
PHASE
50° AT
5kHz
GAIN
SSGND
SYNC
SWB
SWA
LT8582
CHx
8582 F17
PG
RT
V
IN
SHDN
CLKOUT
VC
FBX
GATE
V
OUT
12V
V
IN
5V
100k
215k
R
T
53.6K
6.49k
L1
4.7µH
D1
130k
C
IN
4.7µF
0.1µF 4.7nF
47pF
C
OUT
22µF