LT1766EGN#TR Linear Technology, LT1766EGN#TR Datasheet - Page 12

• Manufacturer Part Number: LT1766EGN#TR
• Description: IC SW REG STP-DWN 200KHZ 16-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1766EGN#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 54 V
• Current - Output: 1.5A
• Frequency - Switching: 200kHz
• Voltage - Input: 5.5 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LT1766EGNTR

LT1766/LT1766-5
APPLICATIONS INFORMATION
where:
Peak-to-peak ripple current (I
and into the output capacitor is typically chosen to be
between 20% and 40% of the maximum load current. It
is approximated by:
Example: with V
and ESL = 10nH, output ripple voltage can be approximated
as follows:
To reduce output ripple voltage further requires an increase
in the inductor value or a reduction in the capacitor ESR.
The latter can effect loop stability since the ESR forms
a useful zero in the overall loop response. Typically the
inductor value is adjusted with the trade-off being a
physically larger inductor with the possibility of increased
component height and cost. Choosing a smaller inductor
with lighter loads may result in discontinuous operation
but the LT1766 is designed to work well in both continuous
or discontinuous mode.
Peak Inductor Current and Fault Current
To ensure that the inductor will not saturate, the peak
inductor current should be calculated knowing the
maximum load current. An appropriate inductor should
then be chosen. In addition, a decision should be made
whether or not the inductor must withstand continuous
fault conditions.
12
ESR = equivalent series resistance of the output
capacitor
ESL = equivalent series inductance of the output
capacitor
dI/dt = slew rate of inductor ripple current = V
I
I
V
=
dI
dt
LP P
P-P
RIPPLE
0 0465 0 0085 55
-
=
.
=
=
47 10
( )
40 47 10
(
=
V
•
40
OUT
+
(
(
0 465
( )( )( )
IN
−
.
V
.
)(
IN
6
( )
= 40V, V
•
V
5 40 5
=
IN
A
(
f L
10
)( )
–
−
=
6
0 1
6
V
)(
−
.
OUT
• .
OUT
200 10
0 85
mV
)
+
)
= 5V, L = 47μH, ESR = 0.1Ω
LP-P
(
10 10
P-P
•
) through the inductor
•
3
)
=
−
9
0 465
)( )
.
10
6
A
(
0 85
IN
.
/L
)
If maximum load current is 0.5A, for instance, a 0.5A
inductor may not survive a continuous 2A overload con-
dition. Dead shorts will actually be more gentle on the
inductor because the LT1766 has frequency and current
limit foldback.
Peak switch and inductor current can be signifi cantly higher
than output current, especially with smaller inductors
and lighter loads, so don’t omit this step. Powdered iron
cores are forgiving because they saturate softly, whereas
ferrite cores saturate abruptly. Other core materials fall
somewhere in between. The following formula assumes
continuous mode of operation, but errs only slightly on
Table 2
VENDOR/
PART NO.
Coiltronics
CTX15-1P
CTX15-1
CTX33-2P
CTX33-2
UP2-330
UP2-470
UP2-680
UP2-101
Sumida
CDRH6D28-150M
CDRH6D38-150M
CDRH6D28-330M
CDRH104R-330M
CDRH125-330M
CDRH104R-470M
CDRH125-470M
CDRH6D38-680M
CDRH104R-680M
CDRH125-680M
CDRH104R-101M
CDRH125-101M
Coilcraft
DT3316P-153
DT3316P-333
DT3316P-473
VALUE
(μH)
100
100
100
15
15
33
33
33
47
68
15
15
33
33
33
47
47
68
68
68
15
33
47
(AMPS)
0.97
0.75
1.35
2.4
I
1.4
1.1
1.3
1.4
1.9
1.7
1.4
1.4
1.6
2.1
2.1
2.1
1.8
1.5
1.5
1.3
1.8
1.3
DC
1
(OHMS)
0.087
0.099
0.277
0.062
0.069
0.044
0.095
0.058
0.093
0.225
0.126
0.106
0.146
0.076
0.122
0.173
0.158
0.120
DCR
0.08
0.06
0.09
0.19
0.11
HEIGHT
(mm)
4.2
4.2
5.9
5.9
5.9
5.9
3.8
3.8
3.8
3.8
6
6
4
3
6
6
4
6
6
5
5
5
3
1766fc