LT3755-1 LINER [Linear Technology], LT3755-1 Datasheet - Page 16

• Manufacturer Part Number: LT3755-1
• Description: 60V 4-Switch Synchronous
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LT3791
For high efficiency, choose an inductor with low core
loss. Also, the inductor should have low DC resistance to
reduce the I
inductor current without saturating. To minimize radiated
noise, use a shielded inductor.
R
R
current comparator threshold sets the peak of the induc-
tor current in boost operation and the maximum inductor
valley current in buck operation. In boost operation, the
maximum average load current at V
16
SENSE
SENSE
I
OUT(MAX _ BOOST)
Figure 7. Maximum Peak-to-Peak Ripple vs Duty Cycle
is chosen based on the required output current. The
Selection and Maximum Output Current
200
180
160
140
120
100
80
60
40
20
0
2
50
R losses, and must be able to handle the peak
I
SENSE(MAX)
55
BUCK ∆I
60
BG1, BG2 DUTY CYCLE (%)
=
65
L
LIMIT
/

 
BOOST ∆I
I
70
R
SENSE(MAX)
51mV
SENSE
75
80 85
L
/
LIMIT
–
∆I
2
90
IN(MIN)
L

 
95
3791 F07
•
100
V
IN(MIN)
V
is:
OUT
where ΔI
operation, the maximum average load current is:
The maximum current sensing R
operation is:
The maximum current sensing R
operation is:
The final R
R
to 30% margin is usually recommended.
C
In boost operation, input current is continuous. In buck
operation, input current is discontinuous. In buck opera-
tion, the selection of input capacitor, C
need to filter the input square wave current. Use a low ESR
capacitor sized to handle the maximum RMS current. For
buck operation, the input RMS current is given by:
IN
SENSE(MAX)
I
I
R
R
OUT(MAX _ BUCK)
RMS
and C
SENSE(MAX)
SENSE(MAX)
= I
L
OUT
is peak-to-peak inductor ripple current. In buck
SENSE
LED
in both the boost and buck operation. A 20%
Selection
2
=
=
value should be lower than the calculated
•D+
2 •I
2 •I
=

 
LED
LED
2 • 47.5mV
∆I
47.5mV
R
12
L
SENSE
• V
– ∆I
2
2 • 51mV• V
•D
OUT
L(BUCK)
+
SENSE
+ ∆I
SENSE
∆I
2
L
L(BOOST)

 
value for the boost
IN
value for the buck
IN(MIN)
, is driven by the
• V
IN(MIN)
3791f