LTC3122_15 Datasheet, PDF (18/26 Pages) Linear Technology – 15V, 2.5A Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3122
Applications Information
V_IN
5V
C_IN
4.7µF
L1
3.3µH
OFF ON
BURST PWM
SW
V_IN
V_OUT
SD ^LTC3122
PWM/SYNC
CAP
R_T
57.6k
RT
V_CC
SGND
FB
V_C
PGND
C_VCC
4.7µF
C1
100nF
R_PL
604k
C_PL
10pF
1.02M
R_C
127k
C_C
220pF
R2
C_F
113k
33pF
V_OUT
12V
800mA
C_OUT
22µF
3122 F06
Figure 7. Boost Converter with Phase Lead
The circuit in Figure 7 shows the same application as
that in Figure 5 with Type III compensation. This is ac-
complished by adding C_PL and R_PL and adjusting C_C, C_F,
and R_C accordingly. Table 4 shows the parameters used
to generate the bode plot shown in Figure 8.
Table 4. Bode Plot Parameters for Type III Compensation
PARAMETER
VALUE
UNITS
COMMENT
V_IN
5
V
App Specific
V_OUT
12
V
App Specific
R_L
15
Ω
App Specific
C_OUT
22
µF
App Specific
R_ESR
5
mΩ
App Specific
L
3.3
µH
App Specific
ƒ_OSC
1
MHz
Adjustable
R1
113
kΩ
Adjustable
R2
1020
kΩ
Adjustable
g_ma
95
µS
Fixed
R_O
10
MΩ
Fixed
g_mp
3.4
S
Fixed
η
80
%
App Specific
R_C
127
kΩ
Adjustable
C_C
220
pF
Adjustable
C_F
33
pF
Adjustable
R_PL
604
kΩ
Adjustable
C_PL
10
pF
Adjustable
From Figure 8, the phase margin is still optimized at 60°
and the crossover frequency remains 15kHz. Adding C_PL
and R_PL provides some feedforward signal in Burst Mode
operation, leading to lower output voltage ripple.
170
150
130
110
90
70
50
30
10
–10
–30
0.01
180
140
PHASE
100
60
20
–20
GAIN
–60
–100
–140
–180
–220
0.1
1
10 100 1000
FREQUENCY (kHz)
3122 F08
Figure 8. Bode Plot Showing Phase Lead
3122fa
18
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