LT1766EFE#TRPBF Linear Technology, LT1766EFE#TRPBF Datasheet - Page 13

• Manufacturer Part Number: LT1766EFE#TRPBF
• Description: IC REG SW HV 1.5A 200KHZ 16TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1766EFE#TRPBF

• 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-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
the high side for discontinuous mode, so it can be used
for all conditions.
EMI
Decide if the design can tolerate an open core geometry like
a rod or barrel, which have high magnetic fi eld radiation,
or whether it needs a closed core like a toroid to prevent
EMI problems. This is a tough decision because the rods
or barrels are temptingly cheap and small and there are
no helpful guidelines to calculate when the magnetic fi eld
radiation will be a problem.
Additional Considerations
After making an initial choice, consider additional factors
such as core losses and second sourcing, etc. Use the
experts in Linear Technology’s Applications department
if you feel uncertain about the fi nal choice. They have
experience with a wide range of inductor types and can tell
you about the latest developments in low profi le, surface
mounting, etc.
Maximum Output Load Current
Maximum load current for a buck converter is limited
by the maximum switch current rating (I
rating for the LT1766 is 1.5A. Unlike most current mode
converters, the LT1766 maximum switch current limit
does not fall off at high duty cycles. Most current mode
converters suffer a drop off of peak switch current for
duty cycles above 50%. This is due to the effects of slope
compensation required to prevent subharmonic oscilla-
tions in current mode converters. (For detailed analysis,
see Application Note 19.)
The LT1766 is able to maintain peak switch current limit
over the full duty cycle range by using patented circuitry*
to cancel the effects of slope compensation on peak switch
current without affecting the frequency compensation it
provides.
*Patent # 6, 498, 466
I
PEAK
=
I
OUT
+
(
I
LP P
2
-
)
=
I
OUT
+
( )(
V
OUT
( )( )( )( )
2
P
V
). The current
V
IN
IN
–
f L
V
OUT
)
Maximum load current would be equal to maximum switch
current for an infi nitely large inductor , but with fi nite
inductor size, maximum load current is reduced by one-
half peak-to-peak inductor current (I
formula assumes continuous mode operation, implying
that the term on the right is less than one-half of I
For V
L = 20μH:
Note that there is less load current available at the higher
input voltage because inductor ripple current increases.
At V
conditions:
To calculate actual peak switch current with a given set
of conditions, use:
Reduced Inductor Value and Discontinuous Mode
If the smallest inductor value is of most importance to a
converter design, in order to reduce inductor size/cost,
discontinuous mode may yield the smallest inductor solu-
tion. The maximum output load current in discontinuous
mode, however, must be calculated and is defi ned later
in this section.
I
Continuous Mode
I –
I
I
I
OUT(MAX)
P
OUT MAX
OUT MAX
SW PEAK
IN
OUT
(
= 15V, duty cycle is 33% and for the same set of
(
I
(
LP-P
2
= 5V, V
)
)
)
=
= I
=
=
=
=
=
=
P
1 5 0 21 1 29
1 5 0 44 1 06
1 5
I
1 5
I
OUT
OUT
.
.
.
IN
.
−
(
−
−
−
−
= 8V, V
V
+
+
2 20 10
2 20 10
OUT
.
.
(
(
I
(
(
(
L -P
LT1766/LT1766-5
V
5 0 63 15 5 0 63
5 0 63 8 5 0 63
P
2
OUT
+
+
+
=
=
F(D1)
•
•
V V
2
.
F
.
( )( )( )
.
+
.
L f V
)
−
−
(
V V
2
= 0.63V, f = 200kHz and
)
6
6
)
F
A
A
( )( )( )
(
)(
(
IN
)(
L f V
)
(
200 10
200 10
−
−
LP-P
IN
−
IN
V
OUT
−
•
•
– .
). The following
– .
IN
V
OUT
–
3
3
)
)
V
( )
( )
)
15
F
8
–
)
)
V
13
P
F
.
)
1766fc