LTC3124_15 Datasheet, PDF (22/28 Pages) Linear Technology – 15V, 5A 2-Phase Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3124
APPLICATIONS INFORMATION
From Figure 9, the phase is ~60° when the gain reaches
0dB, so the phase margin of the converter is ~60°. The
crossover frequency is ~10kHz, which is more than six
times lower than the 94kHz frequency of the RHP zero to
achieve adequate phase margin.
The circuit in Figure 10 shows the same application as
that in Figure 8 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 5 shows the parameters used
to generate the bode plot shown in Figure 11.
From Figure 11, the phase margin is still optimized at ~60°
and the crossover frequency remains ~10kHz. Adding CPL
and RPL provides some feedforward signal in Burst Mode
operation, leading to lower output voltage ripple.
Table 5. Bode Plot Parameters
PARAMETER
VALUE
V_IN
V_OUT
R_L
C_OUT at No Bias
C_OUT at 12V Bias
R_ESR
LA, LB
5
12
8
22 × 2
14 × 2
2.5
4.7
f_SWITCH
1
R1
113
R2
1020
g_ma
100
R_O
10
g_mp
3.4
η
90
R_C
71.5
C_C
470
C_F
120
R_PL
787
C_PL
12
UNITS
V
V
Ω
µF
µF
mΩ
µH
MHz
kΩ
kΩ
µS
MΩ
S
%
kΩ
pF
pF
kΩ
pF
COMMENT
App Specific
App Specific
App Specific
App Specific
App Specific
App Specific
App Specific
Adjustable
Adjustable
Adjustable
Fixed
Fixed
Fixed
App Specific
Adjustable
Adjustable
Adjustable
Adjustable
Adjustable
LB
4.7µH
V_IN
5V
SWB
CAP
LA
4.7µH
PGNDB V_OUTB
SWA
V_OUTA
LTC3124
PGNDA
C1
100nF
C_OUT
22µF
×2
V_OUT
12V
1.5A
V_IN
SGND
BURST PWM
C_IN
10µF
PWM/SYNC SD
V_CC
FB
RT
V_C
C_VCC
4.7µF
R_T
28k
C_C
470pF
OFF ON
R_PL
787k
C_PL
12pF
R1
1.02M
R_C
71.5k
C_F
120pF
R2
113k
C1: 100nF, 16V, X5R, 0805
C_IN: 10µF, 10V, X5R, 1206
C_OUT: 22µF ×2, 16V, X5R, 1210
C_VCC: 4.7µF, 10V, X5R, 1206
LA, LB: COILCRAFT XAL5030-472ME
3124 F10
Figure 10. Boost Converter with Phase Lead
45
90
30
45
PHASE
15
0
GAIN
0
–45
–15
–90
–30
–135
–45
100
1k
10k
FREQUENCY (Hz)
–180
100k
3124 F11
Figure 11. Bode Plot Showing Phase Lead
3124f
22
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