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LTC1265CS датащи(PDF) 12 Page - Linear Technology

номер детали LTC1265CS
подробное описание детали  1.2A, High Efficiency Step-Down DC/DC Converter
PDF  16 Pages
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производитель  LINER [Linear Technology]
домашняя страница  http://www.linear.com
Logo LINER - Linear Technology

LTC1265CS датащи(HTML) 12 Page - Linear Technology

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12
LTC1265/LTC1265-3.3/LTC1265-5
22
µH
0.125
Ω
VOUT
3.3V
0.8A
COUT
1000pF
100pF
3900pF
1k
0.1
µF
CIN
D1
PWR VIN
VIN
SW
PGND
SENSE+
SENSE–
SGND
ITH
CT
LTC1265 F08
SHDN
LTC1265-3.3
VIN
5V
+
+
APPLICATIONS INFORMATION
Figure 8. Design Example Circuit
Figure 9. Design Example Efficiency Curve
Design Example
As a design example, assume VIN = 5V, VOUT = 3.3V, IMAX
= 0.8A and f = 250kHz. With this information we can easily
calculate all the important components.
From (1),
RSENSE = 100mV/0.8 = 0.125Ω
From (2) and assuming VD = 0.4V,
CT ≅ 100pF
Using (3), the value of the inductor is:
L
≥ 5.2(105)(0.125)(100pF)3.3V = 22µH
For the catch diode, a MBRS130LT3 or 1N5818 will be
sufficient in this application.
CIN will require an RMS current rating of at least 0.4A at
temperature, and COUT will require an ESR of (from 5):
ESRCOUT < 0.25Ω
The inductor ripple current is given by:
IRIPPLE
=
VOUT + VD
L
)
)
tOFF = 0.22A
At light loads the peak inductor current is at:
IPEAK = 25mV/0.125 = 0.2A
Therefore, at load current less than 0.1A the LTC1265 will
be in Burst Mode operation. Figure 8 shows the complete
circuit and Figure 9 shows the efficiency curve with the
above calculated component values.
LOAD CURRENT (mA)
0.01
70
75
80
85
90
100
0.1
1.0
1265 G11
95
L = DALE LPT4545-220 (22
µH)
VOUT = 3.3V
CT = 100pF



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