LT1725CS Linear Technology, LT1725CS Datasheet - Page 22

• Manufacturer Part Number: LT1725CS
• Description: IC CNTRLR ISOLATD FLYBACK 16SOIC
• Manufacturer: Linear Technology
• Type: Flybackr

Specifications of LT1725CS

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Frequency - Switching: 50kHz ~ 250kHz
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Voltage - Output: -
• Voltage - Input: -
• Power - Output: -
• Other names: Q1122680

LT1725
TELECOM 48V TO ISOLATED 15V APPLICATION
The design in Figure 9 accepts an input voltage in the
range of 36V to 72V and outputs an isolated 15V at up to
2A. Transformer T1 is an off-the-shelf VERSA-PAK
#VP5-0155, produced by Coiltronics. As manufactured, it
consists of six ideally identical independent windings. In
this application, three windings are stacked in series on
the primary side and two are placed in parallel on the
secondary side. This arrangement provides a 3:1 primary-
to-secondary turns ratio while maximizing overall effi-
ciency. The remaining winding provides a primary-side
22
TYPICAL APPLICATIO S
34.0k
3.01k
1%
1%
R3
R4
C6
1nF
8
7
FB
V
OSCAP
C
C10
100pF
6
3V
C7
47pF
SFST
OUT
9
R14
820k
R15
33k
3
UVLO
t
ON
10
14
R5
51k
U
ENDLY
13
R6
51k
MENAB
+
LT1725
Figure 9. 48V to Isolated 15V Converter
12
R7
51k
BAS16
R1
24k
C1
22µF
R
D5
OCMP
4
R8
6.2k
V
CC
15
R10
18Ω
R
V
IN
CMPC
5
TM
C2
1.5µF
×3
C8
0.1µF
SGND
ground-referred version of the flyback voltage waveform
for both feedback information and providing power to the
LT1725 itself.
Capacitor C7 sets the switching frequency at approxi-
mately 200kHz. Optimal load compensation for the trans-
former and secondary circuit components is set by resistor
R8. Output voltage regulation and overall efficiency are
shown in the accompanying graphs. The resistor divider
formed by R14 and R15 sets the undervoltage lockout
threshold at about 32V, with a hysteresis band of about 2V.
The soft-start and 3V
VERSA-PAK is a trademark of Coiltronics, Inc
11
MBRS1100
I
SENSE
PGND
D3
1N5257
D4
1N5257
GATE
D2
1
16
2
5.1Ω
R12
R11
150Ω
C3
100pF
51Ω
C9
470pF
R9
10
VP5-0155
7
6
3
4
9
5
8
•
•
•
•
M1
IRF620
T1
R2
0.1Ω
1725 F09a
OUT
•
12
1
features are unused as shown.
•
11
2
MBRD660
D1
+
C4
150µF
1µF
C5
R13
750Ω
1W
V
15V
OUT
1725fa