LTC3703EG-5#TR Linear Technology, LTC3703EG-5#TR Datasheet - Page 21

• Manufacturer Part Number: LTC3703EG-5#TR
• Description: IC BUCK/BOOST SYNC ADJ 5A 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost)r

Specifications of LTC3703EG-5#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 55.8 V
• Current - Output: 5A
• Frequency - Switching: 100kHz ~ 600kHz
• Voltage - Input: 9.3 ~ 60 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

BOOST values greater than 60° usually require Type 3
loops for satisfactory performance.
Finally, choose a convenient resistor value for R1 (10k is
usually a good value). Now calculate the remaining values:
APPLICATIO S I FOR ATIO
C
R
R
C
R
C
R
(K is a constant used in the calculations)
f = chosen crossover frequency
G = 10
absolute gain)
TYPE 2 Loop:
R
TYPE 3 Loop:
C
C
K
K
3
3
B
B
2
2
2
2
1
1
=
=
=
=
=
=
=
=
=
=
=
=
C K
C K
tan
tan
2
2
K
2
V
2
2
V
(GAIN/20)
R
OUT
π
π
π
OUT
π
π
2
2
−
V
V
( )
1
( )
f K R
2
⎛
⎜
⎝
• • •
• •
• • • •
• •
REF
REF
1
K
⎛
⎜
⎝
BOOST
f G R
f C
f G K R
f C
K
2
1
−
BOOST
1
−
−
( )
−
( )
•
1
1
R
R
V
2
V
1
1
1
1
1
4
REF
REF
(this converts GAIN in dB to G in
3
U
1
+
+
45
1
45
U
°
⎞
⎟
⎠
°
⎞
⎟
⎠
W
U
Boost Converter Design
The following sections discuss the use of the LTC3703-5
as a step-up (boost) converter. In boost mode, the
LTC3703-5 can step-up output voltages as high as 60V.
These sections discuss only the design steps specific to a
boost converter. For the design steps common to both a
buck and a boost, see the applicable section in the buck
mode section. An example of a boost converter circuit is
shown in the Typical Applications section. To operate the
LTC3703-5 in boost mode, the INV pin should be tied to
the V
mode, pulse-skip operation and the line feedforward com-
pensation are disabled.
For a boost converter, the duty cycle of the main switch is:
For high V
by the LTC3703-5’s maximum duty cycle which is typically
93%. The maximum output voltage is therefore:
Boost Converter: Inductor Selection
In a boost converter, the average inductor current equals
the average input current. Thus, the maximum average
inductor current can be calculated from:
As with a buck converter, choose the ripple current to be
20% to 40% of I
determines the inductor value as follows:
The minimum required saturation current for the inductor
is:
I
D
I
V
L
L MAX
L(SAT)
OUT MAX
(
=
CC
=
V
V
voltage (or a voltage above 2V). Note that in boost
(
∆
IN MIN
OUT
)
> I
I
(
OUT
V
L
=
OUT
•
L(MAX)
)
1
–
f
I
to V
=
)
O MAX
−
V
(
•
L(MAX)
D
IN
1
D
V
–
MAX
IN
IN MIN
MAX
+ ∆I
D
(
)
ratios, the maximum V
MAX
. The ripple current amplitude then
=
L
)
/2
I
O MAX
≅
(
14
V
)
IN MIN
•
(
V
LTC3703-5
IN MIN
V
(
)
O
)
OUT
is limited
21
37035fa