LT1310 LINER [Linear Technology], LT1310 Datasheet - Page 10

• Manufacturer Part Number: LT1310
• Description: 1.5A Boost DC/DC Converter with Phase-Locked Loop
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT1310
Using the circuit of Figure 1 as an example, the following
table shows the parameters used to generate the Bode plot
shown in Figure 5.
Table 4. Bode Plot Parameters
From Figure 5, the phase is 120 when the gain reaches
0dB giving a phase margin of 60 . This is more than
adequate. The crossover frequency is 50kHz, which is
about three times lower than the frequency of the right half
plane zero Z2. It is important that the crossover frequency
be at least three times lower than the frequency of the RHP
zero to achieve adequate phase margin.
10
PARAMETER
R
V
C
V
C
ESR
C
C
g
g
V
R
R
C
R
OUT
OUT
C
C
g
g
R
R
R
R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK
f
C
ma
mp
L
IN
S
C
OUT
ma
mp
L
O
C
C
C
L
O
: COMPENSATION CAPACITOR
: COMPENSATION RESISTOR
: OUTPUT RESISTANCE DEFINED AS V
: OUTPUT RESISTANCE OF g
: TRANSCONDUCTANCE AMPLIFIER INSIDE IC
: POWER STAGE TRANSCONDUCTANCE AMPLIFIER
R
: OUTPUT CAPACITOR
Figure 4. Boost Converter Equivalent Model
O
–
+
g
mp
VALUE
820
500
4.7
1.5
5.6
1.6
30
15
12
10
g
2
5
ma
U
+
–
FB
U
ma
UNITS
mho
MHz
M
m
k
mho
REFERENCE
pF
V
V
H
F
1.255V
OUT
DIVIDED BY I
W
COMMENT
Application Specific
Application Specific
Not Adjustable
Adjustable
Adjustable
Application Specific
Application Specific
Not Adjustable
Not Adjustable
Application Specific
Adjustable
Not Adjustable
1310 F04
R1
R2
LOAD(MAX)
C
OUT
U
R
L
V
OUT
Diode Selection
A Schottky diode is recommended for use with the LT1310.
The Microsemi UPS120 is a very good choice. Where the
input to output voltage differential exceeds 20V, use the
UPS140 (a 40V diode). These diodes are rated to handle an
average forward current of 1A. For applications where the
average forward current of the diode is less than 0.5A, an
ON Semiconductor MBR0520 diode can be used.
Setting Output Voltage
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation:
A good range for R2 is from 5k to 30k.
R
1
R
–100
–180
–200
2
–50
100
50
Figure 5. Bode Plot of Figure 1’s Circuit
0
0
100
100
1 255
.
V
OUT
V
1k
1k
–
FREQUENCY (Hz)
1
FREQUENCY (Hz)
10k
10k
60
100k
100k
1310 F05a
1946 F05b
1M
1M
1310f