Datasheet

LT8582
28
8582f
APPENDIX
Note that the maximum output currents of g
mp
and g
ma
are finite. The output current of the g
mp
stage is limited
by the minimum switch current limit (see the Electrical
Specifications) and the output of the g
ma
stage is nominally
limited to about ±12A.
From Figure 15, the DC gain, poles and zeros can be
calculated as follows:
DC GAIN:
A
DC
=(g
ma
•R
O
)•g
mp
• η •
V
IN
V
OUT
•
R
L
2
⎛
⎝
⎜
⎞
⎠
⎟
•
0.5R
2
R
1
+ 0.5R
2
Output Pole:
P
1
=
2
2•π •R
L
+ C
OUT
Error Amp Pole:
P2=
1
2•π •(R
O
+ R
C
)C
C
Error Amp Zero:
Z1=
1
2•π •R
C
•C
C
ESR Zero:
Z2=
1
2•π •R
ESR
•C
OUT
RHP Zero:
Z3 =
V
IN
2
•R
L
2•π •V
OUT
2
•L
High Frequency Pole:
P3 >
f
s
3
Phase Lead Zero:
Z4 =
1
2•π •R1•C
PL
Phase Lead Pole:
P4 =
1
2•π
0.5 •R
1
•R
2
R
1
+
0.5R
2
•C
PL
Error Amp Filter Pole:
P5=
1
2•π •
R
C
•R
O
R
C
+
R
O
•C
F
,C
F
<
C
C
10
Figure 15. Boost Converter Equivalent Model
8582 F15
C
C
: COMPENSATION CAPACITOR
C
OUT
: OUTPUT CAPACITOR
C
PL
: PHASE LEAD CAPACITOR
C
F
: HIGH FREQUENCY FILTER CAPACITOR
g
ma
: TRANSCONDUCTOR ERROR AMPLIFIER INSIDE THE CHIP
g
mp
: POWER STAGE TRANSCONDUCTANCE AMPLIFIER
R
C
: COMPENSATION RESISTOR
R
L
: OUTPUT RESISTANCE DEFINED AS V
OUT
/I
LOADMAX
R
O
: OUTPUT RESISTANCE OF gma
R1, R2: OUTPUT VOLTAGE FEEDBACK RESISTOR DIVIDER
R
ESR
: OUTPUT CAPACITOR ESR
M: CONVERTER EFFICIENCY (~88% AT HIGHER CURRRENTS)
I
VIN
C
PL
C
F
–
+
–
+
1.204V
REFERENCE
C
C
R
C
R
O
R2
R1
V
OUT
R
L
R2
FBX
g
ma
g
mp
Mt7
IN
V
OUT
t*
VIN
R
ESR
C
OUT