LT1777CS Linear Technology, LT1777CS Datasheet - Page 19

• Manufacturer Part Number: LT1777CS
• Description: IC SWREG STP-DWN LOWNOISE 16SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1777CS

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.24 ~ 30 V
• Current - Output: 700mA
• Frequency - Switching: 100kHz
• Voltage - Input: 12 ~ 48 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

Basic 3.3V Output Application
Figure 10 shows a circuit similar to the previous example,
but modified for a 3.3V output. Once again, Efficiency and
Internal Power Dissipation graphs are shown in Figure 11
for input voltages of 12V, 24V and 36V, and for sense
inductor values of 0 H, 1 H and 2.2 H. It is interesting to
note that internal LT1777 dissipation is very close to the
5V example. This confirms the fact that internal LT1777
TYPICAL APPLICATIONS
10V TO 40V
V
IN
C1: PANASONIC HFQ ELECTROLYTIC
C2: AVX D CASE TPSD107M010R0080
C3, C4, C5: NPO OR X7R
C6, C7: Z5U
D1: MOTOROLA 100V, 1A SMD SCHOTTKY
MBRS1100
+
C1
39 F
63V
U
C4
100pF
C6
0.1 F
R3
12k
Figure 10. Basic 3.3V Output Application
C5
100pF
C3
2200pF
12
14
3
SHDN
SYNC
V
C
LT1777
SGND
L1: SENSE INDUCTOR CAN VARY FROM 0 H TO 2.2 H
L2: COILCRAFT D03316-154 OR SIMILAR (SEE TEXT)
V
IN
10
7
AS PER APPLICATION. GRAPHICAL DATA TAKEN WITH:
1 H = D01608C-102, COILCRAFT OR SIMILAR
2.2 H = D01608C-222, COILCRAFT OR SIMILAR (SEE TEXT)
V
V
SW
V
CC
FB
D
4
6
5
13
dissipation is largely determined by input voltage, load
current and sense inductor, and is only a weak function of
output voltage.
The data as shown were performed using an off-the-shelf
Coilcraft DO3316-154 as the main inductor. This is a cost-
effective inductor using an open style of construction. For
a toroidal style inductor, the Coiltronics CTX150-4 or
similar may be substituted.
0 H TO 2.2 H
(SEE BELOW)
L1
D1
150 H
L2
+
C2
100 F
10V
C7
0.1 F
R1
20k
1%
R2
12.1k
1%
1777 F10
V
3.3V
OUT
LT1777
19